Carb questions

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dman

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04 vmax
So I did a full rebuild of the carbs, adjusted the float levels to 18.5, or whatever Sean's picture was, synced the carbs and test drove it today.. it ran wonderful.. 0 to 130 mphs with vboost.
Only problem is there's a cylinder misfire at idle, Rear driver side I believe. When I turn in the a/f screw all the way the misfire stops, if I back it out more then 1 full turn it starts misfiring again.. anybody have an idea of what's going on? The rest of the cylinders at sitting at 3 to 4 full turns out.
I visually look at each spark with bike running and they all looked identical.
 

apsolus

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3 or 4 turns is probably to many. and usually when you have issues that change or go away with mixture screw adjustments the problem is to big or small of a pilot jet. my bike has size 40 pilots at 2.5 turns out , what are you running?
 

apsolus

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i wonder though, i cant get my bike to idle at 1200 rpm hot even with the idle adjustment fully backed off . maybe i need to add some turns to the mixture screw or do a proper sync? i only ever bench sync carbs. i usually get away with it..
 
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i wonder though, i cant get my bike to idle at 1200 rpm hot even with the idle adjustment fully backed off . maybe i need to add some turns to the mixture screw or do a proper sync? i only ever bench sync carbs. i usually get away with it..

I would 100% recommend vacuum synchronizing the carbs, especially if you've done a bench synchronization. If some of the carbs are out of adjustment (as in their throttle plates are adjusted too far open) that can cause the engine to idle high in spite of idle adjustment. I've had

Another thing to check is that your throttle cables are not adjusted to be to tight. In some cases too much tension on the throttle cables can stop the throttle plates from closing completely.

As for the original post, did you check compression? Not that I think it would be low compression, but I could be helpful just to rule that out.
 

dman

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I would 100% recommend vacuum synchronizing the carbs, especially if you've done a bench synchronization. If some of the carbs are out of adjustment (as in their throttle plates are adjusted too far open) that can cause the engine to idle high in spite of idle adjustment. I've had

Another thing to check is that your throttle cables are not adjusted to be to tight. In some cases too much tension on the throttle cables can stop the throttle plates from closing completely.

As for the original post, did you check compression? Not that I think it would be low compression, but I could be helpful just to rule that out.

Compression is 170 on three cylinder and 180 on that driverside rear.. I am suspicious of that cylinder, I checked the coils and they all tested out fine. No smoke out the pipes engine has 12k.
I guess the question is what's going on with the cylinder when I put the screw all the way in? Why would that keep it from misfiring.. I don't think that shuts off the cylinder in any way.. Is it misfiring because it's running too rich like a bad float needle or fuel level? I'm stumped.
 

dman

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Everything is stock on the bike including the jet sizes
 

dman

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3 or 4 turns is probably to many. and usually when you have issues that change or go away with mixture screw adjustments the problem is to big or small of a pilot jet. my bike has size 40 pilots at 2.5 turns out , what are you running?
My jets were:
37.5
170
90
152.5.
The bike runs flawlessly all the way up to 130, but at ideal that one cylinder is misfiring. Yea always sync then adjust. Also setting your floats a little bit on the lean side is a must from what I've read. Here's the pic Sean sent me that I followed.
 

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apsolus

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yeah pull them back off and redo them again. i always use carb cleaner and compressed air and make sure all the ports flow just like the other carbs. i like to compare them all while im cleaning them. if 3 carbs do this and the 1 carb doesnt then you found your problem.
 

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