1979 OMC 250 HP I/O Miss and backfire

D

Dale Klosner

Recruit
Joined
Jun 16, 2008
Messages
1
The engine is a Ford 351 with a replacement OEM OMC long block that has less than 200 hours. My problem is it misses and backfires at cruise to high speed ( 3200 rpm + ). I have changed plugs, plug wires, points, condenser, rotor, distributer cap, coil, checked timing ( at various rpm ), rebuilt the carborator, installed new fuel pump, replaced gas filter, bypassed the gas tank and run on cruise-a day. I am prepared to start over again if someone out there thinks something I did needs repeating. Advancing the timing seemed to temper the backfiring, but not cure. HELP!
 
Last edited:
jerryjerry05

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,926
Re: 1979 OMC 250 HP I/O Miss and backfire

You say the coil and points and cond are new.If the points are closing it will cause this.Check the play in the distributor.The cam could be wore the points pick-up bent.Run it with the dwell meter on.Dwell should stay constant.
Start it up and set idle to 1000 -1200 spray starting fluid at the base of the carb and around the intake.If spraying makes a difference in the idle then your sucking air at the gaskets.Jerry
 
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