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why does my bike backfire?

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If you still have the stock fuel screw you can loosen the carb boots and rotate the carb enough to adjust the fuel screw. Just use a little flathead and your good to go! Be sure to tighten the boots back though...:thumbsup:

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I am also having this problem with my 09. It started out with stock jetting(40 pilot and 182 main). I switched the jetting to a 42 pilot and a 180 main with the fuel screw at 2 turns out. Before I switched the jetting I was getting some decel pop and it started to idle like crap. I took the float bowl of the carb and found some dirt and cleaned that. Than when I took out the pilot I noticed that it was clogged. I cleaned what I could and switched to the 42 pilot and 180 main and ran it for about 2 hours and really didn't see any change. Today I ran it for no more than an hour and was getting more decel pop than when I had the stock jetting. What is going on? Also, I noticed that it is pretty much impossible to get to the fuel screw without taking the carb off. Is there an easier way to get to it or should I try buying an aftermarket adjustable fuel screw? Please help me because this is really pissing me off!

The erratic running problems you describe sounds like a fuel delivery problem.

You should do a complete cleaning of the carb, including the accelerator pump circuit. Then set the AP pump timing screw acc. to the manual.

Although the aftermarket screws and covers are cool and tempting to buy, they can never make up for a problem that lies elsewhere.

The bike does not backfire like crazy with the stock leak jet. In fact, it is just fine. The leak jet is not the problem.

I have a question, when you put in the #42 pilot jet, how hard did you tighten it? If these jets are overtightened the calibrated holes in them can be deformed, causing rough and lean running...

There is also the chance of an exhaust leak. loosen the header pipe at the clamp junction behind kick starter, then loosen the 2 nuts at the head.

Then wiggle the header a bit up and down to find the sweet spot and retighten the 2 nuts evenly. After this you can tighten the midpipe clamp.

I rode my -09 a week ago. I had a #42 pilot jet and a 180 main jet. Fuel screw at 2 turns out. Everything is stock.

It was 3 degrees Celsius (37 F).

The bike had no backfires, no decel pop and no bogging. No matter how fast i wicked the throttle on it didn´t bog.

If it ran fine in this weather I´m 100% sure that you can get yours running good too. No need (at this point) to buy aftermarket stuff, it can run good anyway.

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The erratic running problems you describe sounds like a fuel delivery problem.

You should do a complete cleaning of the carb, including the accelerator pump circuit. Then set the AP pump timing screw acc. to the manual.

Although the aftermarket screws and covers are cool and tempting to buy, they can never make up for a problem that lies elsewhere.

The bike does not backfire like crazy with the stock leak jet. In fact, it is just fine. The leak jet is not the problem.

I have a question, when you put in the #42 pilot jet, how hard did you tighten it? If these jets are overtightened the calibrated holes in them can be deformed, causing rough and lean running...

There is also the chance of an exhaust leak. loosen the header pipe at the clamp junction behind kick starter, then loosen the 2 nuts at the head.

Then wiggle the header a bit up and down to find the sweet spot and retighten the 2 nuts evenly. After this you can tighten the midpipe clamp.

I rode my -09 a week ago. I had a #42 pilot jet and a 180 main jet. Fuel screw at 2 turns out. Everything is stock.

It was 3 degrees Celsius (37 F).

The bike had no backfires, no decel pop and no bogging. No matter how fast i wicked the throttle on it didn´t bog.

If it ran fine in this weather I´m 100% sure that you can get yours running good too. No need (at this point) to buy aftermarket stuff, it can run good anyway.

I will try the exhaust to see if that fixes it. I don't think that I over tightened the pilot, I just snugged it. It is also nice to know about lossening the boots on the carb and spinning it to get to the fuel screw. I'll definatly try these things before buying any aftermarket parts, and I'll let you know how it goes. Thanks.

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Do what i did. sent my carb to TokyoMods. no more popping on decel(its not a backfire just a sign of a the bike running lean) idles great no bog anywhere and very responsive. but hey if u did that u wouldnt learn how to jet:banghead: ! no really though learning to jet is important to get the most outa your bike in different riding conditions. kinda cool when u know what to do when it acts a certain way and u know how to fix it.:thumbsup:

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I will try the exhaust to see if that fixes it. I don't think that I over tightened the pilot, I just snugged it. It is also nice to know about lossening the boots on the carb and spinning it to get to the fuel screw. I'll definatly try these things before buying any aftermarket parts, and I'll let you know how it goes. Thanks.

Beware that the header pipe seals against a copper crush washer. Do not tighten it harder than needed, or it will become totally flat and might not seal that good.

But not so loose that it falls off! hehe you get the idea...

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I have in my mind dicovered the problem. I have taken the carb apart about three or four times now and everytime I find dirt in the float bowl. I have since changed the fuel to something I know is absolutly pure. I also put an in line fuel filter in with a different fuel line to try and clean it up for a tank or two. It kept clogging the pilot whitch I thought would make it run lean. I just don't understand how dirt was or still is getting in there. It now has clean fuel, the carb boots are sealed and tightened good, and the air filter is clean and sealed good. How is it getting in???? Please help!!

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I also run an inline filter on all of my bikes, and it does catch trash that the petcock screen misses.

Dirt can also enter through the carb vent hoses.

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Alright, so everything got worked out. I ended up taking the carb completely apart and cleaning every little thing so I knew it was absolutly clean. I also went with the 180 main, 42 pilot, and f.s. 2 turns out. The decel pop is pretty much completely gone and it is running the way I feel it should be running. It still has a bog if you mat the throttle while it is on the stand, but this isn't felt at all when on the track. I've narrowed it down to the leak jet and the accelerator pump causing the bog. I'm happy with the way it rides for now, but I think that in the near future I am going to want to get rid of the bog. I have searched a few things on here and found that guys with 450s are modding their ap linkage, or something like that, to get rid of these bogs. Do any of you guys know about doing this to a 250? Also, what other leak jets have you guys found to work better than the stock size? I know I have asked this already, but should I just cough up the money for an R&D adjustable leak jet and adjustable fuel screw to speed up the whole testing process? I just hate having to rip the bike down 5 to 10 times to get it perfect. Either way, Southwick this weekend!!

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You can use an o-ring i.d. 10mm and put over the A.P. actuating arm. It will speed up the return stroke of the a.p.

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You can use an o-ring i.d. 10mm and put over the A.P. actuating arm. It will speed up the return stroke of the a.p.

You don't happen to have any pics of this do you? I know that you are pretty good with that sort of thing.

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