Carb Question and High

...Idle speed (sorry).

I have a '98 Royal Star Boulevard with the 28mm carbs and the 4 into 4 exhaust. A PO installed 4 pod K&N filters, Nasty Boyz 4x4 exhaust, and rejetted. I installed baffles and had to rejet.

I found the thread for the Big Foot mod, and I used the setting they recomended (the needle clip setting, 17.5 main jets, and I already had what they suggested for the pilot jets). It ran OK...I did notice a couple of issues though. It seemed like the rpms would hang before dropping back down. I read that was a sign of a lean running engine. I would also sometimes get a "gasp" when I would be coming to a stop, but then didn't need to and gave it some throtle. I checked the jug #1 plug and it seemed to be just a tad (barely noticibly) white.

I thought I would try the next size up main jets. I figured if it was too rich, I would see it in the plugs. I was also concerned that the 4 pods might be letting through more air than the one big K&N filter, so it was concievable that it needed the bigger jet.

After installing the bigger jets (I didn't open or touch the slides/diaphrams or needle settings this time), with the carbs back on the bike and a carb sync performed, I now have a new issue. The bike is idling at about 1200 rpm and I have the Idle Set Screw backed out so far it's not touching the carb. Nothing is caught up in the choke mechanism. I noticed when I screw the PMS in on jug 3 & 4 I can hear the engine bog down, but not so when I do it to jugs 1 & 2. The engine doesn't seem to hang when rpms are dropping.

Any ideas as to what could be causing this?

Maybe check the sync screw on your base carb, could be that your base carb is being held open by the sync screw rather than the idle speed screw. My guess is that not all 4 carbs were perfectly synced and you left it with: that's as good as I can get it. Just maybe?

...Idle speed (sorry).

 

I have a '98 Royal Star Boulevard with the 28mm carbs and the 4 into 4 exhaust. A PO installed 4 pod K&N filters, Nasty Boyz 4x4 exhaust, and rejetted. I installed baffles and had to rejet.

 

I found the thread for the Big Foot mod, and I used the setting they recomended (the needle clip setting, 17.5 main jets, and I already had what they suggested for the pilot jets). It ran OK...I did notice a couple of issues though. It seemed like the rpms would hang before dropping back down. I read that was a sign of a lean running engine. I would also sometimes get a "gasp" when I would be coming to a stop, but then didn't need to and gave it some throtle. I checked the jug #1 plug and it seemed to be just a tad (barely noticibly) white.

 

I thought I would try the next size up main jets. I figured if it was too rich, I would see it in the plugs. I was also concerned that the 4 pods might be letting through more air than the one big K&N filter, so it was concievable that it needed the bigger jet.

 

After installing the bigger jets (I didn't open or touch the slides/diaphrams or needle settings this time), with the carbs back on the bike and a carb sync performed, I now have a new issue. The bike is idling at about 1200 rpm and I have the Idle Set Screw backed out so far it's not touching the carb. Nothing is caught up in the choke mechanism. I noticed when I screw the PMS in on jug 3 & 4 I can hear the engine bog down, but not so when I do it to jugs 1 & 2. The engine doesn't seem to hang when rpms are dropping.

 

Any ideas as to what could be causing this?

There's a lot to consider with so much catalog tweaking going on?

I'll say up front that I am a base line guy and if I aim for performance, I first start with the engineered base line which in this case is completely skewed.

Where would I start? 1st for me is the 28mm and understanding what the aim was for this carb size.

This would suggest to me that each jug has to work more to fill, this becomes a timing/or /duration problem, at least in my mind.

Exhaust is a big deal here as it can severely effect filling volume, I see you are aware and replaced the baffles tho I would remove them at the moment.

I would also check for a vacuum leek at intake 1.

Now what Carl was mentioning, the way for me to avoid not knowing if... is to assemble the set, then bench sync them using at first a handy size drill bit once they are all held equal I set to the book spec. Then working the throttle a couple of times to check and see that they are all landing repeatedly at the bench mark!

I am curious at the pilot screw turn out, this is another potential, to little then too large a jet too much well this one has to be rule on one step at a time..

Do reach out if you want to develop a plan or let us know what your plan is also type of driving.

Patch

While fiddling with this, I found the exhaust pipe for jug #2 is not nearly as hot as the other 3. I'm also getting a lot more "forceful" (for lack of better term) and cooler exhaust coming from jug #2 .

I assume I will never get to the bottom of what's going on with the idle and any issues with the carb/sync until I determine what is going on with the #2 jug. I purchased a laser thermometer and in the next day or so will confirm (with out burning the crap out of my fingers) what the temps are on the header pipes and move forward with addressing the issues with that first.

Thanks,

Rich

PhishHead

Hi Rich, I put together a plan on what I would do if the bike was new to me just based around the combustion cycle.

The info is based on my understandings and why working with the 28 mm is a bit more touchy.

Of course if there is a an unknown issue with no. 2 carb your next go around would be to make sure that carb has clear passages. Sometimes a clean warm sonic bath can help clean hard to find blockages and a can of carb clean with compressed air..

I'll finish it off today and send it off to you if nothing else its an opinion

Steven,

That would be great! I appreciate it.

Rich

PhishHead

...Idle speed (sorry).

 

I have a '98 Royal Star Boulevard with the 28mm carbs and the 4 into 4 exhaust. A PO installed 4 pod K&N filters, Nasty Boyz 4x4 exhaust, and rejetted. I installed baffles and had to rejet.

 

I found the thread for the Big Foot mod, and I used the setting they recomended (the needle clip setting, 17.5 main jets, and I already had what they suggested for the pilot jets). It ran OK...I did notice a couple of issues though. It seemed like the rpms would hang before dropping back down. I read that was a sign of a lean running engine. I would also sometimes get a "gasp" when I would be coming to a stop, but then didn't need to and gave it some throtle. I checked the jug #1 plug and it seemed to be just a tad (barely noticibly) white.

 

I thought I would try the next size up main jets. I figured if it was too rich, I would see it in the plugs. I was also concerned that the 4 pods might be letting through more air than the one big K&N filter, so it was concievable that it needed the bigger jet.

 

After installing the bigger jets (I didn't open or touch the slides/diaphrams or needle settings this time), with the carbs back on the bike and a carb sync performed, I now have a new issue. The bike is idling at about 1200 rpm and I have the Idle Set Screw backed out so far it's not touching the carb. Nothing is caught up in the choke mechanism.I noticed when I screw the PMS in on jug 3 & 4 I can hear the engine bog down, but not so when I do it to jugs 1 & 2. The engine doesn't seem to hang when rpms are dropping.

 

Any ideas as to what could be causing this?

Hi Rich, sorry for the delay. In the PM I will be sending I set the bike up very differently to what I read in the above. However I got the exhaust wrong so this will change my setup a bit and I need to make some changes!

The highlighted above suggest to me that the pilot circuit is wrong and I address it; but you will need to pull all 4 screws and line them up make sure they are in perfect shape and that all the parts are in order and good condition. If 1 & 2 won't trim then you have a problem that can go either way rich or lean.

Anyways given that this engine was designed for the 28 mm then my opinion is that the stuff I have read for mods floating on the net do not account for cams or venturi, I've read some pretty off the wall mods that make no sense to me regarding this model and setup.

I must say that the pipes have been my hurtle in this V4 setup. Personalty I see this for what it is and that is a noisy show, an unfinished thought to the combustion cycle.

So we are running lean or rich? How much can we blame a non scavenging exhaust system?

Another question is, can the "gasp" be a hot carbon spot? With all these oversize jetting not impossible.

Can you tell me if the bike was setup as purposed in this .....

http://www.international-star-riders.com/starcruiser/vol2-7/AirRoyal/AirRoyal.html