I have a 2008 Searay with a 350 Mercury engine. Under 2000 rpms the engine runs fine, but over 2000 rpms the engines is miss firing, making popping noises, and the smell of fumes is great. The replacement of spark plugs did nothing to solve the problem. I also double checked that i was using a non-ethanol fuel. What next should be checked to solve this issue?
Is it fuel injected? Does it have a distributor? Is it really a small block Chevy?
It is fuel injected. No distributor. Unknown.
Fuel filter not allowing enough gas through at higher speeds?
How old is the gas?
Problem started with older gas, treated with conditioner during winter closing. Used the older gas down to less than 1/4 tank then filled with new gas. Still had same problems, but did not change the fuel filter.
How many hours are on the engine and how has it been operated, specifically, has it been run with sustained 4,000+ RPM for most of its life. If yes, unless it has roller lifters you may have a cam lobe going flat.
Fuel filter could get gummed up with old gas. Hope for the cheap fix. Try a fuel filter.
Sea foam might help. You could have water in the gas, or you could have a trip to the mechanic for proper diagnosis.
It is indeed a Chevy 5.7L V8 converted to marine use…Hopefully, a new fuel filter cures it…
I’d go through the ignition components too–coil, cap, rotor, pickup, wires. I don’t know what kind of ignition system you have on this, but it’s possible that something is weak and the problem shows up when there is high demand on the system–eg. at higher RPMs.
Have placed the boat in the hands of a new mechanic and provided him with all your comments. This is the second mechanic. Thanks for the comments.
I will post the cure when it is found!