My Backfiring Wont Stop

[NRPkfx400]

I have tried every thing. Messing with the fuel screw, new pilot jet, cleaned out the float bowl, i even took it to a friends house whos dad is a motor speacioalist and we coan't get it to stop. The one thing we didn't try is changing the fuel to a higher octane. Could this stop the backfiring? What do you think the problem is? Ask any questions and i will answer to help you come up with ideas. Just throw something at me i will try it!

[Speed_MDS2]

Is it backfiring on decel or accel? You mentioned that you've messed with almost everything but the main jet, what main do you have in it and what are the mods done to the bike? You most likely need a bigger main.

[drzoo2]

Are you sure you don't have a leak on your intake boot or exhaust? The intake is easy to find. Use some carb cleaner and spray around the carb boot. If the idle changes you have a leak. It could be a small crack thats hard to see. Check around all your exhaust connections for black escaped exhaust.

Higher octane won't help. It burns slower and is selected based on motor compression. Has nothing to do with backfiring. Like posted above, were in the rpm's is it a problem?

z

[NRPkfx400]

Its only on the decel. Especially when going down hills. Messing with the fuel screw definately has an effect on it. It mostly occurs when im going down a hill with out the clutch in. My friends dad said that the only place that would matter if there was a crack in the boot would be the boot in front of the carb because the carb wouldn't be able to sense the excess air coming in.

[NRPkfx400]

Oh yeah. The current jets are 130 Main, 25 pilot, stock starter jet. Mods are just after market air filter and hmf slip on sport series muffler. When i bought the quad the thing ran great with stock jets. I messd with it and not it won't go away.

[NRPkfx400]

Some how i got it to stop. I just changed the plug which was black and changed the fuel to 89 oct. I don't know why but it stopped.

[NRPkfx400]

Its back. I don't know whats causing it. I changed the main jet to 170 which came with the hmf muffler but i think that is way to rich and it didn't help any. I Mess with the pilot screw and it helps but ii can't get it just right. WTF i can't figure out what is wrong. I found a leak in the exhaust and tightened it down and should be good now. All the boots to the carb are good and free of cracks or holes. Please someone help me!

[NRPkfx400]

I got it for sure this time. My dad was looking through the manual and saw that this quad had a vacum tube or line. That was disconected. Problem solved.

[drzoo2]

The only vacuum tube is the one for the petcock. I can't believe it would run at all with that disconnected? Only on prime.

[jonboy]

Did you remove the airbox lid? If not, try running without it. It is the typical mod for adding a pipe and rejetting. This should lean it out quit a bit.

[NRPkfx400]

No i didn't remove the airbox lid. The vacuum tube was disconected from the carb and was just sitting on top of the motor head. Problem solved.

[kawi_rider_97]

Check the valve clearance.

[NRPkfx400]

Dude i already solved the problem

[airmobile101]

Originally posted by NRPkfx400
No i didn't remove the airbox lid. The vacuum tube was disconected from the carb and was just sitting on top of the motor head. Problem solved.
lol, that happend to me when I put my Hotcams in. The bike would run great until it was put under heavy load. Glad you figured it out!!