hard start, back firing through exhuast, plug getting wet after over 15 kicks

Topic says it all, valves are in spec, has new rings, fresh gas and plug, messed with the fuel screw and sometimes it starts and other times it takes for ever and back fires through exhaust, like a loud bang


Cam timing looked ok, the dots line up with the links, but the dots arnt %100 in line with the angle of the head if you know what I mean.


Any help would be great.





Backfiring thru exhaust can be leaky valves, bad valve timing or ignition timing issue.

When you say the spark plug is wet, wet with fuel I would assume?

Did you do compression test?

Do a compression test.

make sure your carb is not overrunning out of the main jet nozzle, ( meaning float valve stuck open )

double check your valve timing ( cam )

the exhaust cam has two dots, lower left dot lines up with the head / valve cover mating surface. and other dot straight up, intake cam is the opposite with cam dot on lower right and dot straight up. ( in truth the exhaust cam dot on top leans a little to the right. )

the marking on the crank mag is the second to the right as you look in the hole. ( on older kxf's )

If you are certain of the timing, then I would look at carburation, I had issues with starting, just after I changed the clip level on the needle. they are prone to over fuel or under fuel.




When did it last run fine and what if anything did you do to it since?

It's never really started that easily in the 6 months of ownership, but it would start after 5 or 6 kicks, hot start and it would start either second kick or fifteen kicks haha, just pick a random number.

I've done around 12 hours of riding, it became really hard to start the last time I went riding.

I did a cylinder leakage test as the valve clearances were spot on, it was leaking 60% out the crank case and no leakage through exhaust and intake. So i replaced the rings, the bike is a bog standard kx250f with 147 hours.

The bike seems to be running rich as everytime it won't start, il remove the plug and it's wet with fuel. I've checked spark, it's getting fuel obviously.. Compression is great. When it does start it runs perfectly, no hesitating or bogging.

I would look toward the carb on this one then.

set the float height correctly and make sure the float needle is shutting off the fuel.

Also, make sure of the idle fuel screw is set right. usually 2-1/4 -2-3/4 turns out.

I agree with Al. Float level needs to be 7 mm under the top of the bowl. If its over, you get what you have. I would get an R&D remote fuel screw too because that's what I always do and you need to adjust it more than you think.

Sweet, I was guessing it was carb related, will pull it this weekend and check it out. Cheers!

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