Jump to content
Sign in to follow this  

POPPING AND BACK FIRING HELP!!!!!!!

Recommended Posts

hey guys im really freaked out somethings messed up in my brand new bike i just bout a brand new never been riden '04 yz 250f in july ive got about 6 races on it thats all and i noticed when i start it up it back fires and pops loudly when u let off the throttle sometimes even stalling it self even when its warm. now ive taken the cover off the cams and checked all the valves there almost pefectly within specifications. also ive change the fuels ive been using from pump premium all the way up to using vp racing ms 103 and its still doing it pretty heavly im worried there might be a burnt valve or there seating properly so if anyone out there has any information on this subject please post a message please i have a race the 16th!

Share this post


Link to post
Share on other sites

It's not the fuel. Hi octane pump fuel is OK. VP U4 is better. The problem is most likely because the bike is running lean, not enough fuel. Try opening the fuel screw by a half turn and see if this helps. The fuel screw is on the bottom of the carb. Turn it counterclockwise.

I would also double check your air filter to make sure it is seated properly.

Also check the air box where it attaches to your carb and also the rubber boot between the carb and the engine. Make sure everything is attached properly and check the screws to make sure they are snug.

Share this post


Link to post
Share on other sites

Popping generally means lean on the pilog circuit, and opening the fuel screw is a good place to start. Air leaks can also make you lean as stated above.

A good way to check for air leaks is to squirt staring fluid (ether) at all the joints in the carb boot, clamps, hot start and any place there might be a leak while the bike is running at idle. If it speeds up then you've found a leak.

Exhaust leaks (especially at the head) can cause popping too.

Share this post


Link to post
Share on other sites

Did you take the carb apart? I managed to get the plate on the intake side of the slide in upside down. This allows way too much air in and leans the mixture..

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×