GZ250 Backfire after decelration after carb clean

[ggray1979]

2006 GZ250 with only 70 miles. Had carb cleaned at shop because of bad gas during storage. Backfires after all downshifts, etc. No smoke from head. Idle speed too low. Did the shop not reset the carb correctly? Will running a tank of gas through it eventually clear the problem? Thanks. George

[raul10141964]

Idler speed may be to low or the pilot is set wrong , i have my set a 2 1/2 turns and work very well
factory set was 1 1/4 turns

[ggray1979]

Will that help the backfiring issue? Thanks.

[alantf]

Idle speed too low.

There's a big white knob under the carb. With the choke off, & the engine hot, turn the knob until you get an idle speed of 1200-1400 rev/min. :)

Also, you'll find that adding carb cleaner to the petrol will be well worth it.

[ggray1979]

Thank you very much. I will do that today. George

[ggray1979]

Follow up. I talked to the shop that cleaned the carb and they wanted to look at it again. They first recommended that I run a gallon of Startron Enzyme fuel additive through it and I did that. It still has a small backfire just about every time I let off the throttle, especially if I am engine braking. The sound comes from the end of the pipe, and there is no smoke coming out anywhere near the head.

The shop indicated that they weren't expecting to find anything and that the backfiring issue would eventually go away if I keep running the Startron in the gas.

Assuming they don't see anything in the carb is there any other place there could be a problem resulting in this backfiring? This was in storage a long time, but I was assuming a clean carb would put everything right.

Is it realistic to think the backfiring will eventually go away?

Thanks.

[blaine]

Most "popping" on deceleration is caused by a lean setting on the idle mixture.This is a adjustment that cannot be changed by the mechanic,due to EPA laws.But you can easily do this adjustment yourself.Do a search,there are tons of posts on "idle mixture adjustment"
:) :cool:

[dentheman]

Have you checked your spark plug?

My Shadow backfired like crazy and ran poorly when I first got it. A couple tanks of Seafoam eventually stopped some of the backfiring, but it still often popped on deceleration and ran poorly overall, and raw fuel would drip out of the muffler after I parked it. It turned out that 2 of the 4 spark plugs were fouled. The dealer replaced them and she has run perfectly since then.

Unburned fuel going into the exhaust pipes caused the backfire (I don't think backfire is the correct terminology for what was happening).

[jonathan180iq]

Unburned fuel going into the exhaust pipes caused the backfire (I don't think backfire is the correct terminology for what was happening).

Through the exhaust, it's called afterfire.
Backfire shoots back out the intake.

It's a common misuse.

[ggray1979]

Re: GZ250 Backfire after decelration after carb clean

Most "popping" on deceleration is caused by a lean setting on the idle mixture.This is a adjustment that cannot be changed by the mechanic,due to EPA laws.But you can easily do this adjustment yourself.Do a search,there are tons of posts on "idle mixture adjustment"

I looked around and saw a needle shim adjustment being mentioned. Is that what you are referring to? I also saw that someone had drilled out a jet and the richer mix bumped up his top speed. Both of these are above my head!

BTW, the shop went ahead and cleaned the carb again and it seems to have minimized the problem. By setting the idle high (too high) it made a big improvement on afterfire during deceleration/gear changes. I assume this is because the lean mixture causes the problem at lower, idle-like rpms. Very irritating at a stop light to hear all that racket. I am bringing the idle speed down slightly to find a happy medium.

I did notice that by going easier on the throttle on gear changes during acceleration (that is no unnecessarily high revving), the afterfiring is essentially gone. Likewise, if I don't get carried away with engine braking the afterfire is just about gone. If I crank down on it getting up to speed entering a busy road the popping returns. I can probably live with that.

The shop owner that did the cleaning swears that the problem will eventually disappear if I just put some serious miles on it and use his favorite fuel treatment "Starttron" enzyme. Since this bike only has 180 miles on it, and did sit in storage for three years, I am hoping he is right. Is this too optimistic? Also, I am assuming that I am not hurting the bike in other ways living with the afterfire. Am I messing my nest?

Thanks.

[alantf]

After reading your last post, and with only 180 miles on the bike, my first suggestion would be to handle the bike a lot more gently, and give the engine a good break in period. You're not doing the engine much good, going hell for leather at this early stage. :)

[Meme]

I think alantf is probably right, you are riding the bike too hard. And remember that the proper idle speed on these bikes is unusually high (1,300 RPMs).

BUT, if the shop owner that "cleaned" the carb thinks you need to run carb cleaner in it (fuel treatment) to fix the problem, I would find another shop to take it to. Carb cleaners you run through the tank are nowhere near as effective as taking the carb apart and cleaning it properly. If the shop doing the work thinks that is the solution, they probably have a long history of improperly cleaning carburetors. There should be nothing to clean out after it has been properly cleaned.