runnin hot,backfire

hello all,I have a 09' yz450 got it from my cousin who raced it a couple seasons. bike ran good and was regularly maint. I was riding it and it just started smoking real bad,when i got home i checked water,and oil. hardly any oil in it. so i broke motor down thinking maybe valve guide seals,or bad rings. looking at the parts  figured id just be done with it and rebuild fresh. so i have replaced piston, rings,new cylinder,valve guide seals. the cylinder was super smooth and really polished looking inside but other than that no obvious signs of anything.I put everything back together,it started right up and idles perfect.when riding down road noticed has a sputter and miss,and is running very hot.(noticed header was cherry red only after a few minutes of riding) never noticed that before. noticed on flyywheel theres 3 marks when setting tdc, i lined up the center mark when i was setting up cams. should ibe lining up the 1st mark, could i be a couple degres out.also noticed my exhaust clearance is slight out .25 would that make that much difference. thanks any help appreciated

From left to right, the first two timing marks are for ignition.  The third one is TDC for cam timing.  Check your work. 

 

Also, if the bike sat a while when it was being rebuilt, you may have a partially clogged pilot jet.  Try pushing a a fine wire through the metering orifice to dislodge any varnish there.

thanks for the reply,thats how I set up I put it on center mark. hopefully that will solve the problem.

thanks for the reply,thats how I set up I put it on center mark. hopefully that will solve the problem.

Running hot and backfiring means it's running lean. If you've have to adjust the idle or it's not idling well then replace your pilot jet.

Well moved mark on the rt to center mark,lined cams up put back together and its still backfiring and header is cherry red in about 5 minutes. starts and idles perfect but still slight miss and backfires. Any more ideas? :banghead:

drive out to grays, fix it, then ride the dez for the weekend.(ride in the day drink at night) .The fuel screw or pilot jet are clogged ,if the cam timing is correct.

drive out to grays, fix it, then ride the dez for the weekend.(ride in the day drink at night) .The fuel screw or pilot jet are clogged ,if the cam timing is correct.

that doesnt sound bad,never been to cali.I could use a 2 week vacation,we've been workin none stop since hurricane sandy! :thumbsup:

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