Engine Problem

[huntingwiley]

Today I was out and boat was running great for about 20 minutes. Then I noticed it started to knock. Then it stoped running. I could get it to start if I gave it gas in netural but it would turn off as soon as I returned to idle. When it was running it was knocking pretty bad. Just before going out I got Gas. Could it be bad gas?

The engine is a Merc 350 Mag MPI.

Thank for any help.

[dogbert]

yeah, probably bad gas. Where did you buy gas?

[chpthril]

Sounds like water in the gas. The number 1 cause of spark knock is high combustion temps. This can be a result of high engine temp or a lean mixture. Water in the gas can cause this by ways: 1) the water takes the displaces fuel, thus resulting in a leaner mixture - less gas. 2) water contains O2, this extra oxygen adds to the lean mixture. So, make sure the distributor did not loosen up and advance the timing, could be low fuel pressure - lean condition, engine water temp - high engine temp, water in fuel - pull filter and try catch it's contents and place in glass jar.

Like Dog said, spoiled gas tends to have a lower volatility, and will pre-ignite

[dogbert]

chpthril...you make sound smarter than I am

[chpthril]

chpthril...you make sound smarter than I am

Tough job, but someone has to do it

[huntingwiley]

I bought gas on the lake at one of the marinas just before I started having problems. I am going to change the fule filter this evening and see what the gas look like. Is there something I can add to the gas to burn trough it or should I just drain the talk. I ask because it is full and it will be a real pain to drain 40 gal.

Thanks

[Tanner]

I've noticed the marinas aren't running 100% gas. Instead they are running the ethanol blend. The ethanol blend only has a 20 day shelf life b4 it begins to seperate.... they say 30, but I've seen it start seperating in 20. If your filling up at a smaller marina, they won't go through their tanks fast enough.

Go out of your way to get fuel that is 100% gas.

[ajholt7]

Or use Sta-Bil Marine.

[huntingwiley]

Removed the water Sep today and the gas in it looked like Choclate milk. I have never seen gas like that. Definitely had some water in it..but what chould have given it that shcu a brown color?