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Question: 86 kawasaki kx 500 backfires on starting?

(Posted by: dirtbikeguy on 2010-03-04 16:20:08)

My 86 Kawasaki KX 500 backfires on trying to start it, It pops out the pipe, on kickover, maybe sitting with bad gas in carb, or need's serviced?

Posted by: CARL G H on 2010-03-04, 16:47:59

Backfiring out the tail pipe is based on timing. in general an engine draws in fuel and air on the down stroke and compresses the mix on the up stroke. the spark hits just past center of the top of the next down stroke and the piston is forces down again as the piston begins to rise up again the exhaust valve opens and allows the fumes from the explosion to escape out the tail pipe. if the valve opens earlier and the spark happens too soon the result is a backfire out the tail end. bad fuel isnt likely the cause as it just causes no start or cruddy running. poor spark maybe. you may have a sticking exhaust or intake valve from setting. does the compression feel good? I would offer a sugjestion though to drain the oil pull the plugs possibly use some trans fluid in the pan and crank it a few times to flush the crankcase and free up sticking parts. remember its a flush so no plugs in the cylinders.. drain the pan again and let it drip clean. put motor oil in and a new filter (if equipped) clean and gap plugs, check point condition and replace if needed.

Posted by: guardrailjim on 2010-03-05, 08:11:00

Fouled spark plugs, or leaking exhaust valves. Change the plugs and adjust the valves.

Posted by: bikerwoody on 2010-03-07, 04:47:24

Carl would be correct if it was a four stroke, but this is a regular problem with two strokes. You should run the engine with the fuel turned off when you finish riding, to clear the fuel/ oil mix from the carb. Then put fresh fuel in when you want to ride again. You will need to clean or replace the spark plug. If all else fails, find a kindly 40 something gentleman to give it to. Hey, that's me!!