2007 moomba mobius lsv engine backfires and runs ruff above idle around 2000 rpm

[michaelwinger]

I bought this boat after it had been sitting for a few years and its running poorly. I changed out the ecm and the rotor and the plug wires and put in a new fuel filter and spark plugs.
I've noticed the numer 6 cylinder plug is unusually dark after just a few hours, darker than the other new plugs and im wondering about a fuel injector stuck open?
Also, I had about a quarter of a tank of old gas, like over two years old. I filled the tank with premium and figured that would take care of any bad gas. perhaps there is more in the tank than i imagine.
any idea's?
the boat starts perfectly and runs pretty good. it just backfires at wide open throttle and sputters around 2000 rpm, especially when im towing a tube with my kids on board..
thanks for your help.
Michael

[sivs1]

welcome to the forum, post up some pics of your boat. Assuming you have the 325 EFI motor, sounds like you did all the key things, premium fuel, fuel filter etc... Add in some Marine Stabil and see if that helps, sounds like a bad gas issue, hopefully it clears up after your burn through a full tank. Am guessing you changed oil and filter as well.

[kaneboats]

Should have unhooked the fuel supply hose and siphoned out every drop of the 2 year old fuel. You can hope this will clear up. Check the plug and plug wire on #6 and consider replacing both. Sometimes you can switch an injector with a different cylinder and see if that is the problem. I can't recall off hand which system I have, much less what they used in 2006. You can post up pics and we will try to help. Mmandley should have some advice better than mine too.

[N2OGTO]

may have a weak fuel pump, enough pressure, not enough volume, if you have a fuel pressure tester that has a way to grab a sample try to get a fuel sample and see if it has bad gas or low volume, if it has low volume it will cause that. but then again it could be just the old fuel trying to run through.

[michaelwinger]

okay, thanks guys. let me try these things and ill let you know.