Join Date: Jan 2012
Location: quebec city canada
Thanks guys,2001 sportsman 500 ho,I do not think it is running lean,when it had the 157.5 i sprayed carb cleaner through the airbox and it stopped backfiring,now just before the flame out the back i get a puff of black smoke,so it is rich.I have 2 questions,
1,if there is a bad leak in the donut,or a hole in the pipe ,not enough back pressure will it cause it to run hot.
2,could it be the timing is out of sync,and not firing at the rite time.is there an advance in timing at higher rpm,cause even when it backfires at higher rpm it will idle all day long perfectly.someone told me the exhaust valve could have a lot of carbon build up and when expands it will not close properly,but it should not idle if that was the case and he agreed.
no gas in the oil,it has 4500 miles on it.