Jh06231987

compedgemarine

for one stop using premium. it is an 8.2 comp motor. it will run cleaner and make more power on 87 octane like it was designed for.

mike tkach

the 500 efi is designed to run on 87 octane fuel,i would think non ethanol would be an improvement.i suspect the non ethanol fuel is not the problem.maybe you got fuel that had water in it.

Crude Intentions

ICDEDPPL

ethanol and non ethanol don`t mix well at all.

VoodooRob

Also have you had your fuel injectors cleaned and flowed professionally? 500 EFI is known for injector issues. BUP has posted on the service and has replacement injectors in the works for the no longer made stock injectors.

mike tkach

merc claims 8.75.ratio.

compedgemarine

all I know is back when we raced a bunch of them, when torn down for refresh none of them worked out to better than 8.2 to 8.4 when the numbers were crunched. of course they also rate them at 500 hp and most of ours were between 520 and 530 hp. depending on how much time was on them. fresh ones were less than ones with a 30 or 40 hours on them. back then at 100-110 hours we would change out the valve springs and lifters as that seemed to be the only real weak spot for them racing. keep in mind that they spent that 100 hours at 4500 rpm and up almost the whole time.

BUP

VR thanks for the plug. I have talked to him as he has reached out to me. the jist is --- fuel samples and all filters need to changed and checked, Fuel pressure testing and ecm scanning and so forth need to be done. also a tune up in the mix. -- check spark plugs very closely and compression testing is also a good start to keep tabs on internal conditions. . and lets not forget the MULTEC fuel injectors here. they are paper weights.. THEY the MULTECS and even injectors in general have a self life just like we do.

WHAT AMAZES me is people will think about carburetors being cleaned and rebuilt with new kits all the time actually everyday plus I get those calls --- I need my carb cleaned and rebuilt --- but people never think about the injectors for that same end... I find that amazing. Keep in mind the injectors are the metering fuel source for any engine just like a carb. The next bit of advice is ALL the marine OEMs even in class bring up that since all products of theirs is EFI --- the INJECTORS and fuel systems are part maintenance and stay on top of it. Fuel samples are a really good indication of what is needed and where to start. quality fuel filters are a must as well.

For the OP I would --- start with the basics --- fuel - air -- spark all of that has to be good and correct - and of course a know marine person to scan the engine.

E 10 in my area has been here fully 100 percent almost 16 years and I do not have issues with it. and is used here by all the locals since day one 16 years ago. Of course for usage in stock and very mild bumped compression ratio marine engines anything above that I would stay away from the average pump gas .

Next I am only a road trip away and have everything to find and fix all and any issues in hand. Just saying. good luck.