backfire once with electric start

hi.last few days i have observe a problem with my blue beast wr450 2003 model. when i try to use the electric start it backfires once and starts fine but it backfires a bit.the battery is brand new and also the valves in spec.it starts at first kick also with the electric start.when i use the kick starter it doesnt backfire,only on use of the electric start.can you consider what i should check?thanks guys.

I would pull the little plastic plug in the center of the left lower case and check to be sure the bolt holding the flywheel on is tight.

The '03's had some issues straight out of the factory and one was they either did not tighten down the flywheel bolt to spec or the taper on the crankshaft that mates up with it was not quite right as lots of the '03's sheared the woodruff key located on that shaft. Usually they spin the flywheel though and will not start after that happens.

It was first thought that they had missed tightening that nut at the factory, but this year also started trashing out the starter clutch, electric

starters, and/or the gears that transmit the drive to the motor off the electric starter.

To fix it right you have to buy a new left side lower outer engine case/cover as well a new starter drive gear that has a built in clutch that does not allow the kickback, if the motor fails to light up, to get back into the starter or started drive gears as this ended up being what was trashing them out.

The fix ended up using parts off of 2004's as they had this issue fixed by the time that next model year came out.

I bet you could do a search on this site and find some info on it.

thanks for your answer.the bike has not any issues with the starter and the flywheel torque is in spec(cam chain change 2 months ago).the problem is that it starts at first kick and also when i use the electric starter but some times a bit backfire(it starts fine although) when i use the electric start(like puff).

Mine had real starting issues from the day I got it. Were so bad I almost always left it and rode an older '99 I have. But no button on it! WAH!!!

It did a weird sort of backfire like you describe for about the first year or so I had it. THAT was how I found out it had lunched the starter clutch.I replaced it and then found out the cause was probably that backfire/starter clutch issue that the "04 mod fixed, so did that as well.

Well it STILL had a geeawd awful time of starting using the button.

I FINALLY went after it big time starting this year when decided to use the'03 fulltime in the woods.

Posted my results/findings in a thread on here about clutch issues. I really believe most of these starting issues with this model were caused by the clutch issue.

Got that all worked out now though so will have to wait and see

backfires are due to an air leak causing lean mixture

 

Check carb to rubber boot & the rubber boot to the head, the exhaust header and most important the header to silencer joint

No where near enough info to help you

 

Fuel screw setting and oring

jetting

Air cleaner condition

Back fire screen condition

Plug life

Age of timing chain

etc etc

On mine I do not think it actually was a backfire that I was hearing but it did sound like one.

I think this sound was due to the starter clutch being so trashed it would actually catch and stall the momentum of the starter motor and make this huge awful CLUNK sound that I was calling a backfire as that was the closest sound to it I have heard. It had a very mechanical clunk and more than once I thought it was the piston hitting a valve or something similar.

It always sounded horrible but I would hit the button again and it usually would start, or make the bad sound again. Would ALWAYS start using kick starter, but what is the point of having a button if it fails to work?

thanks for you replies guys.problem solved.it was an air leak on carb boot.thanks a lot.

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