Engine problem - '85 Mercruiser 170

[scook]

Pertronix electronic ignition last year - starts and runs great (for a while).

Early June ran at approx. 3000 RPM for around 15-20 minutes, ran near idle for a few more minutes before anchoring up to fish - no problems. Maybe a half hour later tried to start up to move a little, idled very rough, wouldn't run up above idle (not in gear - no load). Tried a few times to start again over next hour or two, best it would do is very rough idle, wouldn't run up at all and died.

Yesterday, started with a little gas poured in carb (hadn't been run since Early June), idled and ran great, ran at approx. 3100 RPM for around 20 minutes and noticed RPM's very slowly decreasing, took it down to idle, it got rough and died almost immediately. At idle the oil pressure dropped to near zero - checked oil and it is good. Didn't try to restart - another long trip back on the outboard trolling motor.

Water temp in the river is around 70 degrees if that helps any.

It's got me stumped. Anyone have any ideas?

[smokeonthewater]

Sounds like it may be a fuel problem

[bradford]

Agree with Smoke. Sounds like fuel and possibly water in the fuel.

[spareparts]

does your oil smell like gas? Could be a bad fuel pump leaking gas into the engine, that will make your oil pressure very low and at teh same time cause a fuel delivery issue.

[THEFERMANATOR]

Originally Posted by spareparts

does your oil smell like gas? Could be a bad fuel pump leaking gas into the engine, that will make your oil pressure very low and at teh same time cause a fuel delivery issue.

This is what I was thinking as well. Neighbor went through this on his 4.3L. They didn't put but a small filter after the pump, and it quickly plugged up with rubber from the pump. His carb plugged up, engine would barely idle, and his oil pressure dropped like a rock after a gallon of gas went into the crankcase.

[scook]

I'll do some oil sniffing. Probably should change the fuel water separator filter to be sure it's not water (the tank is full so shouldn't be condensing moisture). I wouldn't think it would start and run great for 20 minutes if the carb was clogged up - this is the second time it's done this. Was leaning toward ignition since it's the only thing that's changed but will work the fuel issues first.

Thanks

[steplift20]

Keeping it simple
A engine needs three things to run
Air
Oil
Gas
I would start there check to make sure all those things are good
Just my 2 cents
I could get lucky sometimes, but definitely check your water separator The gas they sell today is not hood e 10

[scook]

Don't forget spark.

Yeah, I agree - need to check for gas in the oil and address all fuel issues. At the beginning of the season, I emptied the tank thoroughly, drove a few extra miles and filled up with non-ethanol gas and thought this was going to be a trouble free season. 30 year old boat, I guess I've got to expect an occasional problem, but I'd rather it wasn't during fishing season.

[spareparts]

also, if they haven't been replaced recently, replace all your fuel lines, I've been doing that on boats only 5 years old to fix issues. This new fuel whether E or non-E is tough on rubber lines.

[scook]

Hah - Spare, I think you nailed it. I got the boat in '05 because it was doing exactly what it's doing now - ran 20 minutes and died. We changed the fuel line ant it ran OK.

The guy who owned it before me was a complete non-mechanic (knew how to change the oil and that was it). He had lots of money and when he got frustrated with the V-20, he went out and spent $65k on a new 23' Striper WA and told me later that the V was a better boat in the ocean.

They were only going to give him $1700 trade-in for the boat and trailer and he said "no, I love my old boat and I'm not giving it away to a dealer". My daughter did some work for him and got the boat for me for my birthday with the assurance it was going to a good home. I've done a lot of work on it, but I see why he loved his old boat.