Backfiring with flames usually means 2 things1) Rich mixture (lots of fuel). The spark plugs becomes black powdered. Need good carburetor setup (main jet, needle, pilot screw adjustments)2) Poor valve sealing. Damaged valve seats causes that. Need to take apart the cylinder head and grind the valves (procedure that all mechanics know). That means that when the mixture is compressed inside the chamber and ignited part of the mixture explosion escapes from the leaking valve's seat to the exhaust, so concentrated unburnt fuel in the exhaust catches fire and explodes through the exhaust, creating the flame.
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2006 s50 blvd. pipes were changed out before I bought it. Both carb has had kits put in about 1 1/2 - 2 yrs ago. Replaced fuel, added fuel treatment. plugs were ckd, one needed adjusting, did that, something running lean. ?? It was sluggish, has been repaired. Back fires with flames, a lot until you get to 2nd, then it runs great. We have a friend-mechanic, working on it, but is a litle stumped.
Problem w/ float in carb and valve problem. My mechanic is still reviewing. I know I'm not giving enough info for experts to follow me. I/m female and love to ride, not work on mc, but do know when there is a problem.
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