Air/Idle Screws adjustment questions - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 18 (permalink) Old 06-15-2011, 10:14 PM Thread Starter
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Air/Idle Screws adjustment questions

Can turning the screws out too far cause any damage to the motor?
Also, if a bike pops on decel and has no vacuum leaks and has been coastered could turning the screws in stop the deceleration popping or do you always turn them counterclockwise (out) to stop it??
My bike has no leaks, its been coastered, new plugs, runs like a raped ape, has V&H Cruzers on it and with the idle screws backed out 3.5-4 turns each it still pops like a mother on the front cylinder (Brake side exhaust)
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post #2 of 18 (permalink) Old 06-15-2011, 10:22 PM
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Originally Posted by jgcable View Post
Can turning the screws out too far cause any damage to the motor?
Also, if a bike pops on decel and has no vacuum leaks and has been coastered could turning the screws in stop the deceleration popping or do you always turn them counterclockwise (out) to stop it??
My bike has no leaks, its been coastered, new plugs, runs like a raped ape, has V&H Cruzers on it and with the idle screws backed out 3.5-4 turns each it still pops like a mother on the front cylinder (Brake side exhaust)
Betcha a beer you have a leak somewhere...

Do you have washers under the exhaust bolt acorn nuts? With V&H Cruzers, you need them.
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post #3 of 18 (permalink) Old 06-15-2011, 10:51 PM Thread Starter
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Betcha a beer you have a leak somewhere...

Do you have washers under the exhaust bolt acorn nuts? With V&H Cruzers, you need them.
Yes, I put washers under the acorn nuts. I have new crush gaskets too. There are no leaks anywhere that I could find. I used an incense stick that smoke steady. I had the bike running and I moved the smoke all over the motor. No leaks anywhere.
Can you answer the question about the idle screws? My Clymers manual doesn't say anything about adjusting them. Can backing them out too far cause deceleration pop or hurt the motor??
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post #4 of 18 (permalink) Old 06-15-2011, 10:51 PM Thread Starter
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Betcha a beer you have a leak somewhere...

Do you have washers under the exhaust bolt acorn nuts? With V&H Cruzers, you need them.
Where should I look?
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post #5 of 18 (permalink) Old 06-15-2011, 11:05 PM
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Yes, I put washers under the acorn nuts. I have new crush gaskets too. There are no leaks anywhere that I could find. I used an incense stick that smoke steady. I had the bike running and I moved the smoke all over the motor. No leaks anywhere.
Can you answer the question about the idle screws? My Clymers manual doesn't say anything about adjusting them. Can backing them out too far cause deceleration pop or hurt the motor??
Hmmm. To my knowledge you can't hurt anything backing them out. Others will chime in and verify/challenge. 4 1/2 turns is really the limit. You didn't take the baffles or packing out of the V&Hs did you?
What's odd.... it's the right side! The rear cylinder (short exhaust) is usually the side folk have issues. ''Bout all I can offer. Good luck
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post #6 of 18 (permalink) Old 06-15-2011, 11:27 PM
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Check your mixture enrichener (air cutoff) valve on the front cylinder carb to see that the diaphram is in good shape and moving freely. Watch for the spring and a small o-ring on disassembly. Also make sure the VERY small vac passage in the cover is clear.

If you have no vacuum leaks, you might still be lean even with the screw out 4 turns. Check plug color in the front after you get a couple hundred miles on those new plugs. If whitish, your lean. Could be a jet or main jet valve issue.

Try running seafoam in a few tanks of more stable higher octane fuel. Might pop less.

I would probably check carb sync for good measure.

Good hunting ...

~~C8> Ratt
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post #7 of 18 (permalink) Old 06-16-2011, 08:54 AM
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Contrary to what has been said on this forum, V+H does suggest going up to a 135 main jet with the Cruzers regardless of ear shave or not.

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post #8 of 18 (permalink) Old 06-16-2011, 09:06 AM
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Contrary to what has been said on this forum, V+H does suggest going up to a 135 main jet with the Cruzers regardless of ear shave or not.
Good point JM and accurate, however, we have hundreds of V&H users who have not had to make the change. I believe they suggest re-jetting not specifying jet size. BTW: 135 is stock (at least on mine)
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post #9 of 18 (permalink) Old 06-16-2011, 11:59 AM
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The stock main is 132 but my bike had a 125 in it to compensate for elevation....this is why some are different. If you're getting a lot of popping on decel and your screws are out that far then the Pilot jet is probably to small. As far as rejetting for the new pipes a lot say changing the exhaust you wouldn't need to rejet, but every mech I know suggests going up a step on the mains. Changing exhaust means changing back-pressure

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post #10 of 18 (permalink) Old 06-16-2011, 01:27 PM Thread Starter
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I should be able to figure this out. I took the bike to work today. Its a 40 mile ride. Bike ran flawlessly except for the popping on the clutch side exhaust pipe during deceleration. The right side doesn't pop at all.
The clutch side pops constantly during deceleration unless I pull the clutch lever in. If I give the bike a quick blip on the throttle during downshifting or decelerattion it barely pops at all.

There must be some kind of vacuum leak or something I am overlooking. This can't be normal.
I can try backing out the idle/air screw on the brake side of the bike (rear cylinder) a little more but I really think its just about ready to fall out.
I put a dab of silicone on it to keep it in just in case.
Where else should I look for leaks?
I tried smoke and I couldn't find any leaks anywhere.
Bike runs perfect except for the popping. It only has 5200 miles on it and was garage kept from day one so its practically a new bike.
I can live with the popping if I have to but I would prefer not to. I set off a few car alarms going through a neighborhood because of the popping.
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