Help needed - Poor Running & Lack of Combustion in #3 & #4 Cylinders

So, stupid question; If #4 isn't firing, is the spark plug fuel fouled or dry? If you really have a hot blue spark that jumps 1/4"(I think that was this thread) on the # 4 jug, I'd bet the plug is dry, indicating no fuel being aspirated.

 

BTW, these engines will run like a scalded dog on 3 cylinders it's even tough to hear the the miss at idle until you really get used to hearing one run right.

Well I just pulled the plug on #4 and it's all black and carboned up. Not wet, but it's had since Saturday to dry out I guess. This is a brand new plug installed just before the last two rounds of wrenching and trying to diagnose. I'll try and attach some photos but I'm not really clear on how to do that.

As for hearing #4 or not, I'm pretty confident I'm not just overlooking it. When I pull a plug wire on any of the other cylinders I can hear the effect and see the rpm's drop on the tach. Pulling the wire on #4 has no such effect.

Well I just pulled the plug on #4 and it's all black and carboned up. Not wet, but it's had since Saturday to dry out I guess. This is a brand new plug installed just before the last two rounds of wrenching and trying to diagnose. I'll try and attach some photos but I'm not really clear on how to do that.

 

As for hearing #4 or not, I'm pretty confident I'm not just overlooking it. When I pull a plug wire on any of the other cylinders I can hear the effect and see the rpm's drop on the tach. Pulling the wire on #4 has no such effect.

I was not saying you wouldn't hear the difference when you pull the wire on a running cylinder. I was meaning that the hanging throttle and rough idle are probably a separate issue from the cold cylinder. I just did a bad job of implying that.

If my memory serves me correct, is that if the bike is hanging up on decel then the most likely cause is a bad balance between the carbs. Carbs need to be sync'd on the bike and all 4 need to be in line. If one is out, then they are not sync'd. Although there will be some difference if one cylinder isn't firing, it shouldn't make a whole lot of difference to get started with and get things close, seeing as the procedure has to do with the opening of the butterflies only and how much air a particular cylinder sucks in. As a cylinder goes into it's intake stroke it sucks air through the carb and this creates a vacuum below the butterfly, and that is what is being adjusted. If the butterfly is more open, then less vacuum, if the butterfly is closed, higher vacuum. RPMs should be kept in the 950 neighborhood.

I was not saying you wouldn't hear the difference when you pull the wire on a running cylinder. I was meaning that the hanging throttle and rough idle are probably a separate issue from the cold cylinder. I just did a bad job of implying that.

Ahhh, ok. Now I understand.

If my memory serves me correct, is that if the bike is hanging up on decel then the most likely cause is a bad balance between the carbs. Carbs need to be sync'd on the bike and all 4 need to be in line. If one is out, then they are not sync'd. Although there will be some difference if one cylinder isn't firing, it shouldn't make a whole lot of difference to get started with and get things close, seeing as the procedure has to do with the opening of the butterflies only and how much air a particular cylinder sucks in. As a cylinder goes into it's intake stroke it sucks air through the carb and this creates a vacuum below the butterfly, and that is what is being adjusted. If the butterfly is more open, then less vacuum, if the butterfly is closed, higher vacuum. RPMs should be kept in the 950 neighborhood.

Fair point. I guess vacuum could/would be the same irrespective of combustion (unless of course there's no compression - but I've got decent 175 psi showing in #4 ).

Interesting that we're both chasing issues in cylinder #4 . Your very low reading of 60 psi is obviously concerning. Not being familiar enough with these bikes to really know, I wonder if adjusting the valves on that cylinder will be enough to bring the compression back up to within specifications. That's a looooong way to go though. If not, maybe you've got valve/valve-seat issues. Hoping not, for your sake.

Update & New Data. I may be onto something here. Last night after I pulled the #4 plug to inspect, I cleaned it up and reinstalled. Then, I decided to fire it up just, well, just because. Here's where things got interesting. But first I have to provide some details on what I believe(d?) to be a totally separate issue relating to the fuse box. Bike still has the original fuse box with the glass (really Yamaha?!?!) fuses. For a while now I have had a problem with one fuse holder marked "Signal." It is the second from the bottom. Among other things, this circuit includes the digital dash functions and the tachometer. The problem is that one of the fuse holder prongs was weak and would not firmly hold the fuse in place. This would cause the circuit to drop out and (maybe) come back sporadically. Just touching the fuse would using get it to work again. I had previously attempted a repair of the fuse holder with some solder and it seemed like the fix had worked. But then this past Saturday when working on the bike I noticed the issue had returned. I also saw where a small hole had been melted into the fuse box cover over this problematic fuse prong. The bike would still run when the circuit was not completed (fully warmed up and without choke), but the rpm's noticeably went down. I did not experiment further on Saturday and instead just got the fuse to complete the circuit and focused my attention back on cylinder #4 . Upgrading the fuse box to a "blade" style was already on my future "to do" list once I got the bike running right.

So, now back to where things got interesting last night. As I said, I fired the bike up last night. Cold start with full choke and the Signal circuit was working, as I had tach and digital dash functions. Bike started right up, as it usually does. After running a couple of seconds, the fuse lost its contact, having the following effects: tach stopped working (expected), digital dash stops working (expected), and ENGINE RPM'S WENT UP TO AROUND 2000 AND HELD THERE. This surprised me so I began to experiment some. I touched the fuse causing it to make contact again, and the dash and tach came back, and THE RPM'S IMMEDIATELY WENT BACK DOWN. Breaking the fuse contact again (I forget if I did it on purpose or if it did it on its own again) and the rpm's raced back up to 2000 or so and sounded pretty good (still on choke mind you). So, I then I pulled the plug wire on cylinder #4 to see what would happen and........[drumroll]..........I could hear the cylinder cut out and rpm's drop! Pushed the plug wire back on, and rpm's went back up. I tried this a couple of times with the same result! Fiddled with the fuse to complete the circuit again and the rpm's dropped, and when I pulled the plug wire on #4 it made absolutely no difference.

So, then I tried to get the bike to warm up a bit and run off of choke. I didn't have time to get it fully warmed up (it was late, wife and daughter in bed, neighbors to consider, etc.), but I did get it enough to be able to get it mostly off of choke. I couldn't really rev it up much because of the late hour. What I noted though is that rpm's in general were now slightly lower with the Signal circuit open, and that if I pulled the plug wire on #4 the bike would stumble and possibly even stall. With the Signal circuit closed and functioning, the bike then idled a bit higher, but pulling the #4 plug wire would make no difference at all (which is the symptom I have previously always been observing). I would like to go back and start the bike and let it fully warm up and see how it really runs with the fuse removed from the Signal circuit (and possibly adjusting the idle up a bit). Hopefully I can try that in the very near future.

What I do not know or understand at this point is just how this "Signal" circuit relates to the running of the bike. I did look at a wiring diagram on my phone and see that in addition to the turn signals, horn, dash, and tach, something called an EAND relay a California Only Air Solenoid (remember, my bike is a Cali model) are also on this circuit. Doing a little research it appears the EAND is for the anti-dive forks. I can't find any more info on the Cali-only air solenoid. In any event, I do not know how these last two items function and interrelate to the running of the bike, but they are certainly on my radar now as potential causes.

Thoughts? Suggestions? Information about operation and testing of the aforementioned EAND relay and air solenoid?

P.S. - I ordered a new 8-slot fuse block last night and will be upgrading once it arrives.

Thanks for the update, I have been having some similar issues and have too much hubris and not enough cash to pay a mechanic to look at it. Please hang in there, some of us are vicariously suffering through this with you and the tech talk/troubleshooting gives me a daily dose of humility and further expands my understanding of VRs and my 84 garage queen (she might be allergic to riding this year, maybe scared she will catch COVID and is waiting for a vaccine or me to threaten taking her to the dump). In solidarity, I hope you get more miles on your VR this year, hopefully a long trip with 4 cylinders

Thanks for the update, I have been having some similar issues and have too much hubris and not enough cash to pay a mechanic to look at it. Please hang in there, some of us are vicariously suffering through this with you and the tech talk/troubleshooting gives me a daily dose of humility and further expands my understanding of VRs and my 84 garage queen (she might be allergic to riding this year, maybe scared she will catch COVID and is waiting for a vaccine or me to threaten taking her to the dump). In solidarity, I hope you get more miles on your VR this year, hopefully a long trip with 4 cylinders

Thank you for the encouragement and vote of solidarity!

Progress continues. Fuse box has been replaced with newer style blade type fuse holder. Performed "Shotgun" cleaning method on carbs 3 & 4. Pilot screws removed from #3 &#4 and noted that there was no rubber oring for #4 - or at least I could not find/recover it - so I replaced the missing oring with what I hope was the correct size. Bike mechanic friend helped me perform a leak-down test of all four cylinders performed and they looked good - 3% or less. We also disconnected the California emissions stuff and capped the inlet going into carb. #2 . Synchronized carbs (using single gauge that we moved back and forth to different cylinders). Adjusted the seal of the air filter (foam on bottom of filter was completely missing), and got the airbox seated correctly (that was pure fun!). Pilot screws adjusted out to 1.5 out.

So, what was the result? Well, the bike is running better than it ever has since I've owned it. While that it not really saying much I suppose, it spins up quickly and clearly has a LOT more power now. After working on it Saturday night in the garage, the throttle was super responsive and it sounded terrific. It idles nicely at just over 1000 rpm's. That said, it's not all positive. It seems to be "over-fueling" and getting terrible mileage. I took the bike out on Sunday for an extended shake-down ride. I filled the tank and headed out for some back country roads to romp on it some. It was mostly good, but at different points (hard to identify specific throttle position, RPM's) when I would give it a lot of throttle it would give a slight hesitation and not take the throttle as it should, then recover and pull strong. My suspicion is that it's getting to much fuel at those times. More telling was that only 85 miles after filing up, the bars the fuel gauge were all gone and the fuel warning light had even stopped flashing (steady red). Calculated the MPG as only a little over 21 MPG. Yikes. I filled up with another 4 gallons of fuel and this time set to see if my riding was having an undue influence on fuel economy. I headed for the interstate and made a loop around the city on the beltway going around 70-78 MPH (70 MPH limit). After doing another 80+ miles of mostly interstate, the fuel bars were gone again and I gassed upon with another 4 gal or so of fuel. I calculated my mileage this time at just over 22 MPG. Ughh.

Now close to home, I turned off on a side road and really opened her up to see how it would respond, since the sluggishness at some points was quite noticeable. Well, it seemed to like that kind of treatment (even had the oil light kick on), as the throttle response seemed great for the next 2-3 of miles until I got home. I wanted to keep riding and continue experimenting, but alas, I had to head home.

So, I'm not sure what to do next. I'm thinking I'll get it running and check for any vacuum leaks in connection with disabling/disconnecting the Cali emissions stuff. Maybe pull the plugs again and see how they look after Sunday's ride. Beyond that, I'm not really sure what to think as far as why it seems to be over-fueling. Assuming that is in fact what I'm experiencing. I don't have any clear fuel line or the necessary adapters to check fuel levels in each carb., but maybe I need to get some. I did finally breakdown and ordered a 4-carb balancing gauges so I can check the balance again.

a few words on an unfriendly shop keyboard so skip past my spelling...

In all project bike needs a plan. First there is the simple stuff, the obvious things we see and make sense..

Bikes these ages have like mods some well done others just poor attempts.

Start with the basics, compression testing is a basic, leak downs are followups; a for example could be lash issues, cracks, or misaligned ring gaps!

In OP's first postings the compression numbers state, the engine is tight there no leak down is necessary and offers no additional guidance regarding trouble shooting!

This thread is classic volume and ratio issue, period.

And our club has all the tools in the form of experience to get thru such.

The problem on both sides of the net table is trust, ask we answer. Are all problems easy to correct; no and explaining the reasons are technical so choose what and how much you are ready to learn or choose to trust and follow the shared experience.

Electrical problems are the most common with old bikes regardless of brand name.

Like timing angles and combustion pressures the theory is not for every one, but the basics with minimum investment and feedback the club can walk you thru what ever the results are.

Pick a project bike and describe the issues, answer the questions with results and allow our experience to fill in the gaps. It can be a lot of fun and, in the end it remains your accomplishment!

Thanks for the reply Patch. Indeed, I am here seeking guidance and feedback from those more experienced than I. As for gaining a deeper technical understanding - I do so when I am able, while other times I rely on more direct instructions ("do this..." "test that..." "remove and replace this...") when the technical reasoning eludes me.

Based upon prior testing (testing and swapping coils, service manual checks of TCI connections, measuring spark gap), and replacement of plugs, plug caps, and fuse box, at this point I am prepared to mostly rule out my problems as being electrical in nature. Do you agree? I can't fully rule out a screwy TCI without being able to swap in a known good one, but I don't think that's the problem. As I do more reading, I see that it is also possible there could be an issue with the so-called "Boost Sensor," which could be either an electrical or mechanical failure.

I spent some more time testing and tuning in the garage last night, with a focus on the carbs. - the "volume and ratio issue" I believe you were alluding to. Here's what I did and the results:

-Tested for vacuum leaks with propane - none discovered.

-Checked fuel float bowl levels after getting the bike/carbs level - this took several tries for me to get the hang of it, but all 4 seem to be within spec. - around 16 mm below the center-mark on the carb bodies, give or take .5 mm. This actually surprised me, as I expected to find one or more the float levels to be high, as the source of the bike using so much fuel.

-Synchronized the carbs using my brand new 4-gauge carb synchronizer set (Woo Hoo more new tools to play with!). This was performed at 1000 rpm's, per service manual. 2 of the carbs were off a fair amount, but not outrageously so.

Other observations while working on it last night:

-I periodically checked the cylinder temps using my contactless temp gauge (measured at the same point near the exhaust side of each head). Cylinder #4 was still the slowest to heat up. Even after the engine was fully up to operating temps, #4 was 25-35 degrees cooler than the other cylinders, but definitely hot (around 180 was the highest I believe I observed on #4 ).

-I had the bike running around 2.5 hours while I tested and tuned last night - mostly idling, with some occasional revving. I started with a full tank (only 7 miles since filling up) and by the end of the night the fuel gauge was showing only a half (!!!) a tank of gas left.

-the vacuum line coming from the boost sensor is connected to the manifold vacuum port on cylinder #1 . From what I have read in other threads, on the MkII bikes, this is normally connected to the manifold port on cylinder #2 . I can't really see why this would make any difference, but I did come across at least one post where a member said this caused his bike to run poorly.

-Sniffed the exhaust fumes on both sides and while both smelled of unburnt fuel, the right side smelled a bit stronger. That said, I don't regularly sniff exhaust fumes, so this may not mean much.

-Observed an open port on carb. #2 . This appears to be the same port that '83's used to connect the boost sensor hose to (from what I've read here). Does this need to be capped, or should it be connected to anything? Plugging it with my thumb didn't seem to make any difference while running, and propane near it didn't cause rpm's to go up. I believe it went to the charcoal canister previously (which has now been removed).

Action Items:

-I need to pull the plugs again and see what they look like now.

-Test boost sensor & relocate vacuum line to manifold port on cylinder #2

-I also need to take the bike out and check MPG again, but unless I discover a faulty boost sensor, I don't expect I'm going to see much difference based on just the carb. synch I did. At 22 MPG, I'm a looong way off the typical 38-42 MPG I'm reading elsewhere on the forum.

Suggestions for next steps or things to look at beyond the above action items?

Testing the boost sensor is actually quite simple. Pull the vac line from the boost sensor off of whatever carb or manifold port it is attached to. Connect it to a manual vacuum pump(Mighty Vac, etc.) get the bike idling smoothly and then pull a slight vacuum with the manual pump. Be careful as you can damage the diaphragm if you pull too much vacuum. If the idle doesn't change, you either have a bad hose or a bad boost sensor, though if you can see the vacuum on the pump gauge, that pretty much eliminates the hose as the culprit.

Thanks luvmy40. Any approximate range in terms of psi I should use with the Mityvac? Been wondering what is "too much." I've also read that the boost/advance doesn't kick in until near 2000 rpm. Do I need to crank the idle up to 2k to do this test in order to get a meaningful result?

Thanks.

Don't do anything throttle related.

Keep the idle at 1000-1100 rpm. Just give a half a squeeze at a time to to the vac pump. I've done this test without a vac pump, just a vacuum from my mouth.

If you see any vacuum on the gauge and don't see a change in rpm, there is probably an issue with the boost sensor.

Caveat: there probably is a threshold point before the boost sensor has an effect. I just don't know what that threshold is.

All right young fellowand to my brothers: I am back from celebrating a fallen rider, this will be where I am at for the next week.

I haven't the need to know what you have sandmen forgive my french.

This bike has had a volume and ratio issue for a long time.

The reason for this is not Yam's fault.

These bikes produce power leanish, someone read an artical that lead them down the wrong pat. YEt 170 lbs say otherwise!

So from here we must conclude there was still remains a failure.

Its quite simple, one 170 is not a pair, that limits the hunt.

170 is spot on, 190 is a problem.

The reason for linnets is complicated, the highs and lows produce different meanings; this is a clear case of volume and ratio.

That means you have a great bik once you settle this problem.

I was absolutely taken by the 86 and 90 something I ran.

These bikes ae made for those that like to push,pushing means suspension and top end of lean, they are low compression engines as far as performance goes.

So 2 things are wrong: you need reestablish volume and ratio. That means you need first do your very best to blast the cabon out od the jugs which includes the combustion chambers. This sounds like a daunting task but, I can assure you that I have, and it just takes a feeling and, a touch of OCDness,

180 psi will make you proud, but 10 psi is too much for a vacuum actuated CV Carb, just accept what the rules are.

I the thread I posted to you you will find a set of air nozzles I use, they are not fancy nor expensive.

My choice is to drop the headers and the intakes when possible, I soak as described in the "fogging" post then clean up with the air nozzles.

Think a minute, idf the valves per jug are open I will clear the jug, period!

This bike has a base problem, period. There are many here that will walk you thru that with pics and all the patients you can ask for, we just did so on a MK1 so believe me you are in trusted willing hands!

I will continue to monitor but as I said I have somewhat of a full plate and will be heading east for a time.

Every thing you need to scare the pants off of you is already here and willing members to inch you thru!

That bike is a thrill when you help her find her legs, believe me/

I think it would be good to get back to square one.

As you have the plugs out, do another compression check on all 4 cylinders. Engine warm, throttle wide open, all plugs out, wind it over to get highest reading, mark it down.

Check to make sure you have decent spark coming from all 4 wires. Put the same plug on each of the 4 wires, one at a time and check for spark and quality.

Install all components back into engine, making sure the wires clip onto the plug ends. If you don't feel the clip or snap adjust as needed. Fire the bike up again and see if it will run at idle or as close to that as possible. Squirt some carb cleaner or brake clean into each carb and report the differences if any. Try to keep the squirting the same from cylinder to cylinder. Let the engine come back to normal as you move from jug to jug.

Report.

I have some time right now to pitch in and will think on this, put together some ideas.

The vacuum range is 5psi at around idle, as the plate angle opens the vacuum drops, and volume increases: tho on a CV vacuum actuated carb this drop is tricky: The purpose of the vacuum actuated slide is to carry vacuum long - maintained velocity while increasing volume,,, this reduces stumble by either a too rich or too lean condition! Why this works well on these bikes is it produces smooth transition response verse say a slingshot response of a pure sport bike.

There are ways to adjust this throttle response but that isn't the purpose of the thread.

Thanks for the reply Patch. Indeed, I am here seeking guidance and feedback from those more experienced than I. As for gaining a deeper technical understanding - I do so when I am able, while other times I rely on more direct instructions ("do this..." "test that..." "remove and replace this...") when the technical reasoning eludes me.

 

Right then, some hard facts:

 

Based upon prior testing (testing and swapping coils, service manual checks of TCI connections, measuring spark gap), and replacement of plugs, plug caps, and fuse box, at this point I am prepared to mostly rule out my problems as being electrical in nature. Do you agree? I can't fully rule out a screwy TCI without being able to swap in a known good one, but I don't think that's the problem. As I do more reading, I see that it is also possible there could be an issue with the so-called "Boost Sensor," which could be either an electrical or mechanical failure.

 

I spent some more time testing and tuning in the garage last night, with a focus on the carbs. - the "volume and ratio issue" I believe you were alluding to. Here's what I did and the results:

 

-Tested for vacuum leaks with propane - none discovered.

 

-Checked fuel float bowl levels after getting the bike/carbs level - this took several tries for me to get the hang of it, but all 4 seem to be within spec. - around 16 mm below the center-mark on the carb bodies, give or take .5 mm. This actually surprised me, as I expected to find one or more the float levels to be high, as the source of the bike using so much fuel.

 

Ok

-Synchronized the carbs using my brand new 4-gauge carb synchronizer set (Woo Hoo more new tools to play with!). This was performed at 1000 rpm's, per service manual. 2 of the carbs were off a fair amount, but not outrageously so.

 

Other observations while working on it last night:

 

-I periodically checked the cylinder temps using my contactless temp gauge (measured at the same point near the exhaust side of each head). Cylinder #4 was still the slowest to heat up. Even after the engine was fully up to operating temps, #4 was 25-35 degrees cooler than the other cylinders, but definitely hot (around 180 was the highest I believe I observed on #4 ).

 

Liquid cooled bikes need early temp checks within 2 to 3 minutes from start, the reason is heat transfer as the coolant circulates.

 

-I had the bike running around 2.5 hours while I tested and tuned last night - mostly idling, with some occasional revving. I started with a full tank (only 7 miles since filling up) and by the end of the night the fuel gauge was showing only a half (!!!) a tank of gas left.

 

We cannot rely on the fuel gauge for mileage, the correct way is to fuel the tank up, allow it to settle 15-20 seconds, top it off, run it for an hour each way at highway speeds, refill it the same way, how many litters or quarts fit back into the tank? Then check your miles driven, then do the math.

 

-the vacuum line coming from the boost sensor is connected to the manifold vacuum port on cylinder #1 . #1 is 0 to 180* #2 is 180* to 360* plus 70*

Get the picture? It belongs on #2 (left front)

From what I have read in other threads, on the MkII bikes, this is normally connected to the manifold port on cylinder #2 . I can't really see why this would make any difference, but I did come across at least one post where a member said this caused his bike to run poorly.

-Sniffed the exhaust fumes on both sides and while both smelled of unburnt fuel, the right side smelled a bit stronger. That said, I don't regularly sniff exhaust fumes, so this may not mean much.That why we advance timing to provide time to compensate for combustion duration! The signal is expected from the crank and cam angles.

 

-Observed an open port on carb. #2 . This appears to be the same port that '83's used to connect the boost sensor hose to (from what I've read here). Does this need to be capped, or should it be connected to anything? Plugging it with my thumb didn't seem to make any difference while running, and propane near it didn't cause rpm's to go up. I believe it went to the charcoal canister previously (which has now been removed).

 

Unless I am misunderstanding you have an open vacuum port? Now by the same token that port must have been plugged to your sync gauge?

All vacuum leaks or vacuum ports must be terminated there can be no unmetered air, in other words all fresh air intake must enter thru the air box! Anyway the #2 port gets the vacuum advance tube after you check it integrate for cracking or holes.

 

Throttle hanging up is a sing of vacuum leaks

 

 

 

Action Items:

 

-I need to pull the plugs again and see what they look like now.

 

-Test boost sensor & relocate vacuum line to manifold port on cylinder #2

 

-I also need to take the bike out and check MPG again, but unless I discover a faulty boost sensor, I don't expect I'm going to see much difference based on just the carb. synch I did. At 22 MPG, I'm a looong way off the typical 38-42 MPG I'm reading elsewhere on the forum.

 

Suggestions for next steps or things to look at beyond the above action items?

OK, now it is important to accept that 170 psi is the best reading the bike has. That a Venture with only 34K only should not have the carbon buildup this bike has, period! Somebody screwed the pouch some how some way?

The carb circuits are leaking or someone drove with the enricher in the wrong position the plungers are not set correctly, the needles are bad or leaking or not seating not returning, coasting circuits not closing? Resized jets? I don't know but something was very wrong!

You said they were rebuilt but we do not know what was rebuilt. Maybe they have been corrected, we hope so but one thing is for sure you will not have fare performance with those carboned up combustion chambers no way no how, not to mention the difference in between 170 and 190 psi.

I am going to assume that the tech bench sync the carbs before returning them to you? Also that the throttle cables allow all plates to fully close or the sync will be of no value.

I reread the thread I see no mention of addressing the high compression or did I miss it?

Anyways it is time to deal with #4 spark once and for all as I understand it it is the only remaining spark question. It would serve you well to get a gap tester, not expensive and answers the question with no room for doubt.

You said you look at the coils, what coil setup us on that bike, 2 doubles or 4 singles? What is the voltage at the coils, is it close to battery voltage?

Start with moving advance to number #2

Block any vacuum leaks correctly.

measure coil voltage

start decarbonizing

use a proper spark gap tester

Run engine in the dark and check for high voltage shortcuts

Don't do anything throttle related.

 

Keep the idle at 1000-1100 rpm. Just give a half a squeeze at a time to to the vac pump. I've done this test without a vac pump, just a vacuum from my mouth.

 

If you see any vacuum on the gauge and don't see a change in rpm, there is probably an issue with the boost sensor.

 

Caveat: there probably is a threshold point before the boost sensor has an effect. I just don't know what that threshold is.

I was able to test the boost sensor using my Mityvac the other day in the garage and it appears to be working. I didn't go to the trouble of testing voltage, but it did hold a vacuum, and apply and releasing vacuum did make a clearly observable difference in the rpm's. That said, I did not notice any difference at normal idle speeds; however, when I bumped the idle up to 2000, then applied vacuum to the boost sensor, the rpm's went up to around 3000 or so as I recall. I was able to repeat this after multiple attempts. So I feel comfortable ruling this out as a potential problem.

I think it would be good to get back to square one.

As you have the plugs out, do another compression check on all 4 cylinders. Engine warm, throttle wide open, all plugs out, wind it over to get highest reading, mark it down.

Check to make sure you have decent spark coming from all 4 wires. Put the same plug on each of the 4 wires, one at a time and check for spark and quality.

Install all components back into engine, making sure the wires clip onto the plug ends. If you don't feel the clip or snap adjust as needed. Fire the bike up again and see if it will run at idle or as close to that as possible. Squirt some carb cleaner or brake clean into each carb and report the differences if any. Try to keep the squirting the same from cylinder to cylinder. Let the engine come back to normal as you move from jug to jug.

Report.

I did as you suggested and checked compression again with a warm engine (can't swear that it was warm the first time I tested compression. Results were similar to first test, with #4 being the lowest. Here were my readings:

1 = 190

2 = 195

3 = 182

4 = 178

I again verified spark in all 4 cylinders using my new spark gap tester (thanks for the tip on that Patch). Spark looked the same on all 4 cylinders. Same thing with a known good sparkplug. Tried this at varying rpm's and good spark was maintained in all cylinders, including troublesome #4 . Plug leads definitely connected properly with positive engagement of the plug top.

I also inspected the plug condition. #2 & #3 were brownish, and perhaps just a bit lean. #1 was surprisingly rather black and sooty. #4 was black and a bit wet looking, but definitely not soaking wet. I backed the pilot screws out 1/8 on #2 & #3 , and turned #3 in 1/2 turn to try and compensate for what I was observing on the plugs. Plugs were cleaned, tested, and reinstalled, except I put (yet another) new plug in #4 just in case.

Upon your suggestion, I opened the top of the airbox and Squirted carb cleaner into each of the 4 carbs. The effect of spraying into cylinders 1,2,3 was that the rpm's would drop, then take a few seconds to recover to their original level. Spraying into the top of #4 had no effect on engine rpm's. I repeated this being methodical about it, each time with the same result on #4 .

Again, tried pulling off the plug wire on #4 while running and it had no effect at all. This was true no matter what the rpm's when I pulled it off. I tried to check at different throttle positions, but again, no change. I could not really check at half throttle or beyond, as I could not hold it in this position since the engine would still go to redline and beyond. The engine definitely spins up, but it seems to be just 3 cylinders that are making any power.

I did another road test yesterday to see if I could learn anything further. Again, the bike does have power and will spin up - I had it up to 110 mph and it got there reasonably quickly. I can both hear and feel that it's hesitating or struggling some at about 1/8 throttle. This was consistent in gears 1-3, though the rpm range where noticeable was lower for each successive gear. It was most easily observed in 2nd gear around 5000-6000 rpm. By 4th or 5th gear it was getting too hard to detect. I didn't bother filling up with gas again to check mileage, as it was clear that it was still not running right and going through gas much too quickly.

OK, now it is important to accept that 170 psi is the best reading the bike has. That a Venture with only 34K only should not have the carbon buildup this bike has, period! Somebody screwed the pouch some how some way?

The carb circuits are leaking or someone drove with the enricher in the wrong position the plungers are not set correctly, the needles are bad or leaking or not seating not returning, coasting circuits not closing? Resized jets? I don't know but something was very wrong!

You said they were rebuilt but we do not know what was rebuilt. Maybe they have been corrected, we hope so but one thing is for sure you will not have fare performance with those carboned up combustion chambers no way no how, not to mention the difference in between 170 and 190 psi.

I am going to assume that the tech bench sync the carbs before returning them to you? Also that the throttle cables allow all plates to fully close or the sync will be of no value.

I reread the thread I see no mention of addressing the high compression or did I miss it?

Anyways it is time to deal with #4 spark once and for all as I understand it it is the only remaining spark question. It would serve you well to get a gap tester, not expensive and answers the question with no room for doubt.

 

You said you look at the coils, what coil setup us on that bike, 2 doubles or 4 singles? What is the voltage at the coils, is it close to battery voltage?

 

Start with moving advance to number #2

Block any vacuum leaks correctly.

measure coil voltage

start decarbonizing

use a proper spark gap tester

Run engine in the dark and check for high voltage shortcuts

The bike has 4 individual coils. I tested voltage for all coils a few weeks back and all were right on the money per the service manual. I even tried swapping the wiring for coils #3 & #4 to see if the problem would move, and it did not. I also verified good spark (at different rpms) using a spark gap tool (thanks for the tip about this - got a Motion Pro one for cheap on Amazon). Sprayed area around plug wires and coils with water bottle per recommendations here and no problems observed.

I did move the boost sensor hose from #1 to #2 . I also blocked off the port that was sticking out of the bottom left rear corner area of carb #2 . Previously I believe this was just routed to the charcoal canister. I doesn't seem to draw any vacuum, as shooting it with propane made no difference while running, nor did blocking it with my thumb. In any event, it's capped now. To clarify (since you asked about it) when I synched the carbs, this was NOT the port I connected my gauges to - i connected the gauges to the ports on the intake manifolds. To you point though, there are no vacuum leaks and air is ONLY entering through the airbox.

As for decarbonizing the cylinders, and the higher compression figures, I am inclined to wait on this for now. I have read through your prior posts and instructions on high compression numbers and the processes for eliminating the excessive carbon. That may well be warranted for the overall health and running of the bike, but it doesn't seem directly related to issues I'm having with cylinder #4 . The highest compression numbers (after my most recent test) are on the left side of the motor, whereas my problem cylinder that does not appear to be firing (or at least not all the time), has the lowest compression. It seems to me that I need to prioritize the issues specific to cylinder #4 , before turning my attention to clearing the carbon out of the other cylinders. But if my reasoning is flawed or my understanding of the facts is wrong, I am happy to listen.

I know that 4 basic things are needed to support combustion in a cylinder - FUEL, COMPRESSION, SPARK, EXHAUST. From everything I've seen/tested thus far, I don't think compression or spark are missing. So that leaves fuel and exhaust. As to fuel, the carbs seem the most likely culprit. I suppose it is possible there's some obstruction in the header for cylinder #4 that would prevent/limit exhaust, but this seems unlikely. I guess it's possible that the exhaust valves are not opening fully/properly. For that matter, I suppose the intake valves may not be opening fully/properly, thereby limiting the fuel needed for combustion.

As for the prior carb work that was done, my friend/independent motorcycle mechanic is the one who serviced them. He took them down, cleaned in ultra sonic cleaner, checked passageways, measured floats, inspected slides, and installed the 4 new K&L carb kits that came with the bike when I bought it. He also bench synched the carbs. That said, he fully admits this was his first time going around with a set of carbs quite like this setup and allows that he may have missed something. Not having done the work myself, I can't really offer any more details than that.

I think where my head is currently leading me is to pull the carbs again to see if anything is wrong. Patch, I know you stated this would likely be needed in one of your first responses, but I really did not want to hear that at the time. I'm thinking it would probably be good to check the valve lash (and look at the condition of the lobes!) too while I have good access. Again, if I'm heading in the wrong direction, or there are some easier things to try/check first that I haven't already tried, please let me know.

The bike has 4 individual coils. I tested voltage for all coils a few weeks back and all were right on the money per the service manual. I even tried swapping the wiring for coils #3 & #4 to see if the problem would move, and it did not. I also verified good spark (at different rpms) using a spark gap tool (thanks for the tip about this - got a Motion Pro one for cheap on Amazon). Sprayed area around plug wires and coils with water bottle per recommendations here and no problems observed.

Something here is not adding up? So lets focus on it: 1st why would a coil producing spark not spark on #4 only?

Next what would cause spark to increase crush/gap with RPM?

I can think of only 2 reasons: 1st is vibration which would indicate bad connections either to ground or power feed! 2nd would be feed voltage is too low to begin with.

So I would record voltage at coils going in or feed/positive side of coil using the battery ground for negative lead on the meter.

Then using the idle set screw increase the rpm with the rpm adjustment screw, and repeat the test. I would do all 4 coils.

If this shows well like close to battery Volts then you will find a bod ground at the other end and then we'll look at the next step. Remember we are looking for clean voltage on the circuit only, as you have already put the coils thru the impedance tests!

 

I did move the boost sensor hose from #1 to #2 . I also blocked off the port that was sticking out of the bottom left rear corner area of carb #2 . Previously I believe this was just routed to the charcoal canister. I doesn't seem to draw any vacuum, as shooting it with propane made no difference while running, nor did blocking it with my thumb. In any event, it's capped now. To clarify (since you asked about it) when I synched the carbs, this was NOT the port I connected my gauges to - i connected the gauges to the ports on the intake manifolds. To you point though, there are no vacuum leaks and air is ONLY entering through the airbox.

OK I get it, that must be the overflow and vent spout which must vent. That should be attached to a tubing the rest of them as well should be each with its own tube, or you will starve the carb (s) Each carb has a fill spout and a vent, the only vacuum ports are in the intakes.

 

As for decarbonizing the cylinders, and the higher compression figures, I am inclined to wait on this for now. I have read through your prior posts and instructions on high compression numbers and the processes for eliminating the excessive carbon. That may well be warranted for the overall health and running of the bike, but it doesn't seem directly related to issues I'm having with cylinder #4 . The highest compression numbers (after my most recent test) are on the left side of the motor, whereas my problem cylinder that does not appear to be firing (or at least not all the time), has the lowest compression. It seems to me that I need to prioritize the issues specific to cylinder #4 , before turning my attention to clearing the carbon out of the other cylinders. But if my reasoning is flawed or my understanding of the facts is wrong, I am happy to listen.

 

The lowest compression is also this bikes best compression. This is your project and so yours to schedule. That said understanding the big picture is in my experience a better rout. The carbon buildup is a symptom that has now turned into a rather big problem, it must be addressed. You are closer to solving the #4 spark issue so stick to that then decide. But if you are removing the carbs then that would be for me the best time to start because you need access to the valves, and I would add the exhaust ones too. The piston tops alone will not knock these numbers down alone, those exhaust valves and ports must be pretty thick.

Patch, thank you for the replies. I think we are miscommunicating. If that is my fault, I apologize and I will try to be clearer in my meaning. Based upon the tests I performed and my observations, I DO NOT believe I have any problems with spark in cylinder #4 (or any other cylinder). I have good spark in each cylinder under all conditions. I mentioned that I swapped out #3 & #4 coils (without physically moving them from their mounting bracket) - this was only done to confirm that there was no issue with the coils that my other tests had not revealed. I mention pulling the plug wire off of #4 while running. My point in doing this was to see if there was any effect on the running of the engine by pulling spark to #4 - and there wasn't.

I mentioned an earlier post that I could get #4 to fire under some odd circumstances involving removing power to the California emissions solenoid. In thinking about it further, perhaps this was creating a richer condition that allowed #4 to fire properly. Just a hypothesis. I wonder if, instead of spraying carb cleaner into the tops of each carb (which apparently is of the non-combustible variety), I should squirt fuel into the tops of each carb and see how they react. I wonder if that might get #4 to combust, which would comfirm that FUEL is the missing element.

As for the ports on carb #2 - mine has 3 visible ports, not 2. Of course one is the inlet for fuel, another is the drain. Mine has a third port located towards the left rear corner of the carb. I've seen such a port on pictures of members here with '83 Ventures. Maybe this is also something that is on the California models too. Or maybe a prior owner installed a set of '83 carbs on the bike - I really don't have much on the history of the bike or why anyone would do such a thing. This seems unlikely, in any event. I expect this may be something (else) that is specific to the California models.

So 2 comments from me.

How did you determine that you had spark on #4 ?

Carb cleaner or brake clean will both fire a cylinder, as well as WD40,, at least in Canada it will.

I did as you suggested and checked compression again with a warm engine (can't swear that it was warm the first time I tested compression. Results were similar to first test, with #4 being the lowest. Here were my readings:

 

1 = 190

2 = 195

3 = 182

4 = 178

 

I again verified spark in all 4 cylinders using my new spark gap tester (thanks for the tip on that Patch). Spark looked the same on all 4 cylinders. Same thing with a known good sparkplug. Tried this at varying rpm's and good spark was maintained in all cylinders, including troublesome #4 . Plug leads definitely connected properly with positive engagement of the plug top.

 

I also inspected the plug condition. #2 & #3 were brownish, and perhaps just a bit lean. #1 was surprisingly rather black and sooty. #4 was black and a bit wet looking, but definitely not soaking wet. I backed the pilot screws out 1/8 on #2 & #3 , and turned #3 in 1/2 turn to try and compensate for what I was observing on the plugs. Plugs were cleaned, tested, and reinstalled, except I put (yet another) new plug in #4 just in case.

 

Upon your suggestion, I opened the top of the airbox and Squirted carb cleaner into each of the 4 carbs. The effect of spraying into cylinders 1,2,3 was that the rpm's would drop, then take a few seconds to recover to their original level. Spraying into the top of #4 had no effect on engine rpm's. I repeated this being methodical about it, each time with the same result on #4 .

 

Again, tried pulling off the plug wire on #4 while running and it had no effect at all. This was true no matter what the rpm's when I pulled it off. I tried to check at different throttle positions, but again, no change. I could not really check at half throttle or beyond, as I could not hold it in this position since the engine would still go to redline and beyond. The engine definitely spins up, but it seems to be just 3 cylinders that are making any power.

I did another road test yesterday to see if I could learn anything further. Again, the bike does have power and will spin up - I had it up to 110 mph and it got there reasonably quickly. I can both hear and feel that it's hesitating or struggling some at about 1/8 throttle. This was consistent in gears 1-3, though the rpm range where noticeable was lower for each successive gear. It was most easily observed in 2nd gear around 5000-6000 rpm. By 4th or 5th gear it was getting too hard to detect. I didn't bother filling up with gas again to check mileage, as it was clear that it was still not running right and going through gas much too quickly.

So 2 comments from me.

How did you determine that you had spark on #4 ?

Carb cleaner or brake clean will both fire a cylinder, as well as WD40,, at least in Canada it will.

Mach listed that he used the gap tester Carl...

Every thing highlighted in red is related to over fueling!

Pull the carbs, begin loading pics and we'll walk you thru it.

Pull the carbs, begin loading pics and we'll walk you thru it.

Yep,, that would be my direction of advisement.