4.3 Mercruiser backfires @ 4000rpm and above

[90stingray]

Re: 4.3 Mercruiser backfires @ 4000rpm and above

Might be unorthodox but assuming its not the 4.3TKS leave the flame arrestor off and reach in and apply some choke (with a long screwdriver or something) when it starts doing that and see what happens (keep fire extinguisher handy). If it quits backfiring you know its a fuel mixture issue. If you got the TKS, it may be possible you have an issue with that.

Its a regular carbed setup. But i like the idea of giving it some choke to see what happens. Never thought about doing that before... thanks. I have a ton of things to check in the spring. I sure hope i find something wrong.

 

[90stingray]

Re: 4.3 Mercruiser backfires @ 4000rpm and above

Rebuilt the carb again, went back to the stock 160 jets, and used the spring needle and seat... got it dialed in with a vacuum gauge. Changed the distributor sensor. Took her out last night for a test run. As soon as i got past the no wake zone... went WOT and let her run up. We went to 4700 rpm and there was NO BACKFIRE and NO SURGE. Finally, i have a boat that runs like it should! Also, when the motor is hot and we let it sit... she starts just by bumping the key. What a good night.

 

[dsmmace]

Re: 4.3 Mercruiser backfires @ 4000rpm and above

Popping and surging is normally a 'lean' fuel condition, glad you got it figured it out!