Engine sputtering under load

I have a EFI 5.0 Mercruiser with around 350 hours. The last two times I have taken it out it has started sputtering when pulling up a skier/wakeboarder. Once he is up and the boat gets to a higher rpm/mph the engine will get going well and there is no problem. This last for about 30-50 minutes and then it seems to get better to where it is barely sputtering at all. I supected bad gas after the first time and put stable in with a fresh tank, then when it happened the second time I fugured a fuel pump but, I would not think that would improve over time. What ever it is, it is directly related to the load the skier adds since I can not notice it when there is no skier.

Please advise.

-Jordan

Re: Engine sputtering under load

check fuel water separator

when was the last full tune-up??

Re: Engine sputtering under load

I changed the water seperator last summer when it wouldnt start, it turned out to be the coil that time.. It had a tune up from the dealership when I bought it two summers ago.

Re: Engine sputtering under load

every year you need to inspect plugs and compression. the sp's are a tell-tale of the engine, compression should be nearly the same on all cylinders. i inspect sp twice a season. i know some who ck them after every outing. ive found 90 octacne to be the best for pulling skiers and tube. 93 is too high and 87 not enough ump.

Re: Engine sputtering under load

van-man said:

I changed the water seperator last summer

Click to expand...

okay, so check it now - look for water/debris

you gotta start somewhere

Re: Engine sputtering under load

I would start with plugs,if there is water in fuel usually it will "pop" at higher rpm and will not go away after 40 50 mins. if the plugs look ok then check your spark,nice blue arc,wires and coils also usually break down with heat,but sometimes they go the other way and get better,moister ? run it in the dark and look at plug wires that way you can see if spark is jumping out of wires to any ground.check timming to make sure its advancing correctly..thats my few cents wont cost you any $$ to check that stuff