Yzf426 what causes backfire - 2001 Yamaha YZ 426 F

There are many reasons that a vehicle will backfire through the carburetor. What determines the cause depends on what condition the backfire happens. Is it a steady backfire at idle or does it start when you are accelerating ? Do you live in a wet climate or dry? Has the engine been wet?
Backfiring is caused when the exhaust valve is open during the firing or compression stroke of a certain cylinder. For example, a broken spring will not close the valve completely. A bad camshaft lobe will cause a back fire, if you have a distributor that got wet the spark could cross over to another area wire and cause the problem causing a missfire. If the wires were put on wrong after putting in plugs it will cause a missfire.

check first if all cylinders spark plugs are firing, seem like you are missing on one cylinder. this will cause as well backfiring.

if this is not the case then:

backfiring can be caused by too rich fuel mix or by wrongly set advance. there is unburnt fuel present in exorst and this cause backfire. these two are most "popular" causes of the backfiring.

hope this will help you solve the problem, do not forget to vote...

Have the misfire diagnosed and the backfiring will be fixed also. The backfiring is caused by the "over-rich" fuel mixture in the exhaust stream and is igniting within the exhaust. Fix the misfire (which will cause the rich condition) and the backfire will be gone.

Where do wires go on honda x r 125

This is what you needhttp://www.yamahaownershandbook.com.au/lib/download.php?f=5SF-28199-80.pdf
Pdf's page 180 (manual's page 3-18)

Common causes of backfires are:

• Poor or unregulated engine timing is often a cause of intake backfires, but can also be responsible for exhaust backfires
• Improper wiring in the ignition can also lead to timing issues and backfires
• Low fuel pressure, clogged fuel filters, and weak fuel pumps could cause a severe lean air-to-fuel ratio during fuel injection
• Missing or damaged catalytic converter can result in backfires out the tailpipe

Back fire can be caused by different faults.First is to much fuel because of worn carburetter, or wrong adjusments on carburetter. choke sticking will cause backfire. timing be out of adjustment will cause backfire exhaust leak can cause backfire. bad spark plugs, or plug leads , distributer cap worn of cracked will cause backfire as for fuel in muffler, if it combusted in muffler , the muffler would split open it is not that.

the backfire sounds like it was running to lean, check that there is no damge to internal conponents piston ect, is there enough conpression, come across two problems simelar to this, one was my yzf426 it was the hot start that was not seating properly and letting too much air in, another was my mates and this was a duff cdi unit. also check tension on accelorator cable at carb. somtimes they tighten and let too much fuel in. if there is enough compression and it does not seem like there is damage clean the carb and jets and air filter (dont forget to use air filter oil) check intake flange ect for corrosion or damge to gaskets. and also exhaust reaon being it could also be a air leak in the system. hope this helps.

on the carb, it should have a Phillip head screw and a grinded edge as it can be adjusted through hand.

most common problem with new generation four stroke motor....is the valve clearance you may check it at first cause many time the intake valve are two tight and kept open (making motor disfonctional)..we used to have a trick to make that old génération carb work better....twist the throtle 3-4 time before kickstart it..( this will work like a primer and bring gaz in the intake and make that rig started easier)