The Plugs, Cap, rotor and wires are all new. The heads were rebuilt along with rebuilding the engine myself. I guess the only thing I can think of at this point is that the Valve lash is off on one of the valves....I'll have to recheck those (which I was about to do actually). The oil is new and so are the tensioners and timing chains. Oh and to answer your question it backfires out the tail pipe...but not a "bang" more of a hesitation "popping" noise. It sounds like it's happening on one cylinder...looks like it's time to break out the old leak down tester to test the compression of each cylinder. Thanks. Steve --- In dmcnews@xxxx, Heydudetoo@xxxx wrote: > Steve; > When your engine backfires, is it through the intake or out the tail pipe? > An engine that back fires has either an intake or an exhaust valve > open when the gas mixture for that cylinder explores. Carbon buildup in the > engine can stay hot enough to light off gas mixer at the wrong time or the > plug can receive fire at the wrong time. Valves must both (intake & exhaust) > be closed tight when the mixture explores or you will get a backfire. > The most likely thing is carbon in a plug, fire jumping inside the > rotor cap,( bad plug wires cause this) or a weak / broken valve spring. > Pull a couple of plugs, are they carboned up? (black build up around > the tip) If so, put in 6 new ones of the correct rating. The wrong heat > range lets them run to cool to burn off the carbon and you get build up and > back fires. > No carbon on the plugs, pull the rotor cap and check for blacken lines inside > the cap. > Normally jumping fire will blacken this area. If there are black lines > inside the cap replace the cap, rotor and plug wires. > A weak valve spring will give you backfires at high RPM, a broken one will > give you Lots of backfires. > I believe this engine uses oil pressure to keep tension on the timing chains, > how is your oil? > Anyway, just my two cents. > Jerry > Vin# 4890 > > > [Non-text portions of this message have been removed]