i had this problem and i found that i had not tighten my fylwheel nut the right torgue.
jebvtx@sbcglobal.net
June 2007
It may not be the timing. Here are some other causes. Check these first. Lowering engine speed too fast. Gasoline, which contains higher blends of alcohol. Carburetor adjustments set too lean. Muffler construction can induce backfire. Higher than normal engine temperatures. If these solutions don't help check out this site.
http://www.briggsandstratton.com/miscpdfs/RNT/crankshaft-camshaft%20synchronization.pdf
cholbach@yahoo.com
June 2005
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