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CRF 450 backfire HELP!!

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I have a 2004 CRF 450R and last fall started to have a really tough time starting it. Once I got it started and while kicking it over the bike was backfireing really bad. Major flames. Once it ran it still backfired and ran rough. I replaced the spark plug, replaced fuel, checked intake and exhaust valve clearance and both were within Honda range as far as I can tell. Left intake 18mm, rt intake 13mm. Left exhaust .28mm, rt exhaust .30mm. Any words of wisdom out there? I am also loosing engine oil and when i ride and it almost seems like it is leaking from top end to bottom, any thoughs on a remedy?

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the hard starting is your timing .see if it off one tooth .could also be a streched timing chain .back fire can because by a exhaust leak .

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ok you have more than a few issues.

check the timing:

http://www.thumpertalk.com/forum/showthread.php?t=877910&highlight=timing

Other things to check after that:

http://www.thumpertalk.com/forum/showthread.php?t=601361

now for the oil issue, you need new bearings and seals for the counterbalancer and right side crank seal.

do a search on the CRF450 forum for "oil migration"

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