carb tune up help

[Ivan]

After I put the pod filters on, I went up a size on the main jets. I went to 112.5 from 110. I tried some 117.5s, but the top end got a bit soggy.

My main problem is with closed throttle decel. It pops and backfires. Some have said the aftermarket exhaust can cause this, but I think it is much more severe than it should be.

Any ideas?

[egleaves]

I have pods and a 4-1 exhaust, but I don't know my current jet sizes. Mine pops a lot on deceleration; sometimes it sounds a bit excessive, but I think I'm getting used to it. I have noticed that if I hold the throttle open just a hair, the popping lessens or quits all together. I don't know what stops the popping, the additional fuel or the additional air.

[bikerphil]

pop

The main reason for popping on decel is a lean idle mixture. You can try turning the idle mixture screws out 1/8 of a turn. If there is an improvement, repeat 1/8 turn out progressions until you're happy. I find a little popping is normal with a Mac exhaust, 4-1.

[dbeardslee]

I was getting a lot of popping on decel, and adjusted to a little richer mixture. It got a little better, but it was still doing it. Then I checked the timing. It was just a hair advanced, and set it dead on 10 degrees btdc with the vacuum advance disconnected and plugged at the carb tap. Popping stopped.

[Ivan]

You may be on to something. Mine is an 81, which I understand didn't have adjustable timing. The advance mechanism back plate on mine has had the holes slotted out with a round file, so the timing may be off. I put a light on it and the marker was between the marks with the "T" next to them. I have an advance mechanism from an 80, so I may put it on and mess with it. FWIW its an 80 engine in an 81 bike, so I kept the 81 "stuff" on the enine.

[tarzan]

Ivan,do you have the emglo filters.I had some on mine for a while only to find out they were restricting the holes on the lip of the carbs because the rubber boots that come on them is too small.There are guite a few threads on here that describe that problem.

[Ivan]

Yes I ahve the emgo filtersw, but the problem of which you speak is not a problem on my bike. See this.

The timing did help quite a bit. There was enough play to adjust the advance mechanism probably about three or four degrees either way. I retarded it a hair and the popping was drastically reduced to what I would call "normal". Only problem is the top end feel soggy again.

Back to the garage tomorrow....

[TADracer]

You can try to up your pilot jet one size and then adjust your mixture screws again. That probably will take out the rest of the popping.

[tarzan]

On the '79 can you just move the clip on the needle down a notch?That would raise the needle a little and might be enough to adjust it in.