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

  1. #46
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    Default Re: Help needed - Poor Running & Lack of Combustion in #3 & #4 Cylinders

    [QUOTE=Mach VIII;1085140]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.

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

    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.

  3. #48
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    Default Re: Help needed - Poor Running & Lack of Combustion in #3 & #4 Cylinders

    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.

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  4. #49
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    Default Re: Help needed - Poor Running & Lack of Combustion in #3 & #4 Cylinders

    Quote Originally Posted by Mach VIII View Post
    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.
    Quote Originally Posted by Marcarl View Post
    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.

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

    Quote Originally Posted by Patch View Post
    Pull the carbs, begin loading pics and we'll walk you thru it.
    Yep,, that would be my direction of advisement.

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

    Thanks all. I'll post up when I get the carbs off again (sigh).

    Since I'm going to check the valves while I'm at it, is there a good source for the tool that's used to change out shims? Does anyone here have on that is loaned out to forum members or the like? I've got access to shims, but not the tool. Looks like I can purchase for around $60, but I'd rather not for a tool I'll likely only ever use once. [Edit - I'll start a separate thread about this to avoid hijacking my own thread, LOL]
    Last edited by Mach VIII; 09-18-2020 at 11:45 AM.

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