I have a 125 pit bike and it ticks over fine but when you rev it it backfires does any body no how to fix it.

pull cover on magneto and check for loose pickup coil.

remove carb and clean jets , sounds like fuel starvation ! P...

Could be a carbon track on the distributor cap if it has one.

hey mate could be a few things, dirt in the jet easy fix take petrol float off the carb clean jet with w..d. Or there are two screws on the carb one petrol and one air mix the one u want his the petrol one. this will be very close to the accelerator cable and will have a spring on it turn it clockwise. VERY SMALL MOVEMENTS u will hear the engine rev faster as u turn the screw. hope this helps ****

have you tried the idle screw give it a fiddle till its idling at 1500 revs or 1200

2 things need to be done first start your bike get a can of wd40 after your bike is warm and running spray around the carb jointsall 4 of them if your engine changes rpms up or down you have a intake leak ether your carb joint gaskets or o-rings need replacing or your carb joints are old and need replacing. at this point wont hurt to have you carbs cleaned also

some of the other jets are still dirty or it not getting enough fuel, is the float and seat ok

take the carb off clean it out then have a play around with the fuel air mixture,that should fix it.

Clean the carburetor. The idle circuit is plugged up with trash or varnish or a bit of both. Disassemble the carb and soak the parts in denatured alcohol for 30 minutes. Now finish the cleaning with spray carb cleaner. An air hose also helps. The factory setting on the air screw and throttle screw is one and one half turns outward from a lightly seated position.

Just ride it normally. Avoid super high revs when the bike is not in gear and using the power.

Please rate this solution. Thanks bookerm!