miss/backfire

[beanz2166]

Hi all, I put the boat in the water for the first time yesterday and I have what I believe/hope is a small problem. The boat turned over and started right up (which already was more then I expected) we ran it for about 5-7 minutes at various speeds with no issues. After we stopped and ate for about 30 minutes I restarted it and when I started to throttle up I now have a miss/backfire. But heres my kicker. it only happens at 2000-2500 rpm and at wide open throttle (4500 rpm) when I ran between 3000 - 3500 RPM no issues. I bought this boat used and Im assuming (based on the old trailer registration) that it wasnt ran last summer. when I got it, it had 1/4 tank of presumably 2 year old gas in it. I only added about another 1/2 tank to it. Could the old gas be causing my issues? I plan on filling it up with premium the rest of the way and adding to some carb cleaner to the tank. If that does not fix it issue Im thinking new plugs and wires. Am I on the right track with this or am I thinking to small and this could be a bigger issue?


also WOT was 4500 rpm. does this sound right for a 1996 5.7 Merc pushing a 21ft boat?

thanks

 

[achris]

Re: miss/backfire

Bit late now, but what you should have done was to have cleaned out all the old gas (not just added new to it), cleaned the fuel lines, put a new filter in. THEN put new petrol in the tank.

I don't know how much fuel you have in the tank, but that's what I'd be doing now... But now you will also need to pull the carb, clean that out too, and the little filter inside it. I would also be doing a compression test and verifying you haven't done any damage to the engine.

What happens with old fuel is the littler elements evaporate off, leaving the heavy vanish, and a fuel with a lot lower octane rating. This lower octane fuel burns a lot quicker (but yields less energy) than the higher octane (yes I know that sounds wrong, but it isn't). That faster burn is the prime cause of detonation, and detonation kills engines.

New plugs and wires would also be a good idea, but will probably not solve your current problem.

Spec for WOT on your engine is 4400-4800RPM. So 4500 is in spec.

Chris........

 

[beanz2166]

Re: miss/backfire

Just to clarify are you saying that by running old fuel I possibly damaged the engine? Man I hope thats not the case so the fix is drain all fuel clean everything and refuel.

 

[achris]

Re: miss/backfire

Just to clarify are you saying that by running old fuel I possibly damaged the engine? Man I hope that's not the case so the fix is drain all fuel clean everything and refuel.

It's possible, yes.

 

[Bondo]

Re: miss/backfire

Just to clarify are you saying that by running old fuel I possibly damaged the engine? Man I hope thats not the case so the fix is drain all fuel clean everything and refuel.

Ayuh,... It's Possible, in that old fuel don't burn like new fuel, 'n the lean condition is causin' the backfirin', 'n can also cause Detonation...

Fix the Lean condition, 'n the backfirin' oughta go away...