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Discussion Starter #1
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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Newb with a Bullet!
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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.
 

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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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Newb with a Bullet!
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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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Discussion Starter #5
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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Discussion Starter #7
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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Calif Rider
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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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Discussion Starter #9
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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Sparky!!!
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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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Discussion Starter #11
Slim,

I have no blueing of the pipes and no noxious smells. I don't think I have a vacuum leak, but it's entirely possible. I mean something is causing an issue. I started out at 2 1/2 turns out and you could smell how rich it was and there was tons of popping all over the place.

Let me ask you this. What should I do to get to a relatively known state to begin troubleshooting? Set the screws to 2 5/8 or 2 3/4 turns, and balance carbs or should I balance first then set the screws? The reason I ask that is because I don't know if the mixture screws effect vacuum. I would assume not, but you know what they say about assumptions.
 

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Discussion Starter #12
Ok, sorry for the delay, but there has been a lot going on here. Here's where I'm at. I took the carbs off just to check everything once over since my build notes weren't too clear for the carb section. I had the needles reversed for one. But here's my carb jetting:

2 shims under each needle head
40 & 140 front
40 & 142.5 (looks like 142.5) rear

The carbs were slightly out of sync. I did the two bottle method and the rear did not have as much vacuum as the front (small amount). So I turned in the screw about a 1/8 of a turn and it evened out.

The front no longer pops at all, but the rear still pops on deceleration. I've tried different mixture screw settings and turning it in seems to help a little bit. At this point, should I be looking for an air/vacuum/exhaust leak?
 
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