Popping after ear shave, marble, degoat/exhaust, & iridiums - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 12 (permalink) Old 05-13-2009, 09:19 AM Thread Starter
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Popping after ear shave, marble, degoat/exhaust, & iridiums

Hey guys, I just recently got my bike running again after a (mostly) complete rebuild. I have done the following while rebuilding the bike:

Ear shave w/K&N filters
Rejetted - 40 idle and 140/142 mains with 2 shims
Coasters
Jardine exhaust
Iridium plugs gapped at ~.033" - .035"

I started with the air screws out roughly 2 1/2 turns each, but ended up turning them both back in almost a whole turn, which is a lot better, but there is still a whole lot of popping on deceleration and when blipping the throttle.

I used to tune and play around with Chevy TPI fuel injection on my road race camaro. I've just never understood carbs. I've been through the Verses on this, but still have a bit of an issue. I'm guessing the next step is to check the carb balance and adjust from there. But, I wanted to get some input.

Any thoughts?
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post #2 of 12 (permalink) Old 05-13-2009, 09:24 AM
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Man, no clue. Not the world's best or most experienced mechanic but I just had a buddy who is all of those things ear shave, coaster, and degoat my bike and I haven't had a single backfire ever at any time.

It shouldn't make any difference but are your Jardines straight pipes or do they have an "H" between them? Mine are the stock pipes with the Scootworks bypass kit, so no "H" on mine.

If yours has an "H" that is the only real difference I can see. You're in OH, I'm in NE, should be similar elevation and such.

Curious to see what others have to say.

Last edited by krebsne; 05-13-2009 at 09:25 AM. Reason: typo
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post #3 of 12 (permalink) Old 05-13-2009, 09:32 AM
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I am in Chirons corner I have tried every thing and mine still pops on the rear cylinder,Cliffhusn said it is very important to torque the acorn nuts to the proper specs as over tightening will cause a leak as well. And you are correct carbs are nothing but a controlled variable fuel leak that depends on air whistling thru it to make it work.That is why we have fuel injection today, it is precise.




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post #4 of 12 (permalink) Old 05-13-2009, 09:44 AM
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Question on your thread title. You aren't marbled AND coastered, are you? There is nothing to marble when after you coaster, correct?
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post #5 of 12 (permalink) Old 05-13-2009, 11:22 AM Thread Starter
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You are correct, if you "coaster" the bike, you completely remove the air valve from the side of the engine and bolt a block-off plate in it's place. I got a pair of block off plates from a guy on ebay I think.

I'm wondering if I need to pull one of the shims out from under each needle. But I'm going to balance the carbs first, then go from there I think.
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post #6 of 12 (permalink) Old 05-13-2009, 11:24 AM
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Is there any exheast laeks at the head connection? Did you use new gaskets for the new pipes?

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post #7 of 12 (permalink) Old 05-13-2009, 11:32 AM Thread Starter
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That was one of the first things I looked for and couldn't find one. So I'm going to balance the carbs this evening and double check everything. Then I'm not sure where to start after that.
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post #8 of 12 (permalink) Old 05-13-2009, 11:44 AM
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Usually the popping stops or get a lot better after you turn the air screws out not in. Really sounds like something else is the problem. The balancing of the carbs may really to it for you, or like others said it could be the exhaust gaskets. Hope you find the problem.

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post #9 of 12 (permalink) Old 05-13-2009, 11:46 AM Thread Starter
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Well the reason I started turning them in and leaning it out was that you could smell how rich it was running. Hmmm. I'll set them back to stock 1 5/8 roughly and balance and see what happens.
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post #10 of 12 (permalink) Old 05-13-2009, 12:06 PM
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I have a few questions Chiron,
1) are your header pipes turning blue?
2) with the screws in as far as you have them do you smell more of a noxiouse exhast smell?
and 3) are you sure you don't have a vacuum leak?

with that said. the popping on decell and blurping the throttle as you say, is caused by the fuel mixture leaning out too quickly... try adjusting the mixture screws out to 2 5/8 to 2 3/4 turns...I think you will have better luck at those settings
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