86 mercruiser 140 backfire

[Skagital]

My engine has about 4 hours on an overhaul. The first 3 hrs it ran great at rpm from idle up to 4400. Went out yesterday and the engine backfired out the exhaust at about 4000 rpm and then ran sluggish/powerloss. From idle up to 3300 rpm the engine runs fine, anything over that it will eventually backfire again. I'll check the ignition adjustments this weekend, I'm rusty on carb work but any guidance/ideas are greatly appreciated<br />skagital

 

[Trent]

Re: 86 mercruiser 140 backfire

Backfire (really called afterfire) is normally caused by a lean condition. Check the timing to make sure the distributor did not turn (since major work has just been done). <br /><br />Put some Berrymans B12 in the fuel tank (Wal Mart). It really works well. If this does not work your going to have to dive into the carb and clean it and install a kit.<br /><br />

 

[Skagital]

Re: 86 mercruiser 140 backfire

Evidently the night before this all happened, I had changed the valve cover gasket due to a lack of putting the goopy stuff on both sides of the gasket when I originally overhauled the motor. At any rate before getting underway Sunday I found #1 plug wire loose, I believe I pulled it loose during the reassembly of the valve cover, the boat ran fine all day. DUH on me eh! I am fixing to overhaul the carb this winter which will include corrections made by the mercruiser service bulletin No. 88-5 dealing with overrich acceleration bog condition. If you have any info on this would be greatly appreciated<br />thanks AL