Bad Gas - Stuck valves?

[laserbrn]

I went down yesterday to take a look at a 25' skipjack with a 454/Penta 280 setup. The previous owner was a bit dubious as he was selling a family members boat. He ran the boat last week to shoot a youtube video and he ran it on the gas in that was in the tank for a year and a half. According to him, the video, and the neighboring slips, the boat ran fantastically last week and sounded great. He ran it for about 3 hours idling and then took it out for a spin.

Predictably it wouldn't start when I went to take a look at it. I did a compression test and got CRAZY results. Sometimes no compression, sometimes full compression, hopping from cylinder to cylinder I got the same strange results. I went and grabbed a new gauge and same results.

Seems like the valves are all gummed up and made the guy an offer on his boat with a motor not running...needless to say, I got it cheap.

Well, now I want to see if I can get this motor running again and I'm hoping for a little guidance from my friends here!

I know I need to have the carb cleaned/rebuilt and it's a holley 4 barrel so I'll just take it to a carb shop and have them do that work. I've done carbs before and my results have always been better when I have the carb shop do it.

Is there any magic trick to unsticking valves and getting all that gummed up garbage out of there (I've seen it before in smaller engines and just took them all apart)? Can I pull the valve covers off and clean it out is this going to be a waste of time and just repower?

 

[Augie56]

Re: Bad Gas - Stuck valves?

Try a solvent-based additive in the oil. Add what the bottle recommends for unsticking valves and run the engine. I've read that Marvel Mystery Oil is a good choice for this. The oil will be thin, so I probably wouldn't race the engine or go on a long power cruise, either. Of course, change oil once you're done testing/running with the additive. For a couple of bucks and the effort of doing an oil change, you might get lucky and free it up / de-sludge it without having to repower.

 

[picklenjim]

Re: Bad Gas - Stuck valves?

Try a solvent-based additive in the oil. Add what the bottle recommends for unsticking valves and run the engine. I've read that Marvel Mystery Oil is a good choice for this. The oil will be thin, so I probably wouldn't race the engine or go on a long power cruise, either. Of course, change oil once you're done testing/running with the additive. For a couple of bucks and the effort of doing an oil change, you might get lucky and free it up / de-sludge it without having to repower.

Problem is he can't get it started to do that. Pull the valve covers and try to spray something like the Marvel Mystery oil (spray can)to where it will run down the valve stems. Pull out all the spark plugs and shoot some in there. Then crank the engine with the plugs out so it will spin faster with less effort. Watch the valves while cranking and see it any are permanently stuck. Try checking compression again. If this don't work then pull the heads. With those inconsistant compression results the problem is most likely in the heads.

If you start getting some good compression readings siphon all the old gas out and put in fresh. By the way did you ask see the youtube video?

 

[Don S]

Re: Bad Gas - Stuck valves?

Before I did anything, I would check for spark, and if you have spark squirt some gas into the carb to prime it and see if it fires off.
1.5 year old gas will not be holding valves open. A little rust yes, just from sitting.

 

[laserbrn]

Re: Bad Gas - Stuck valves?

I saw the youtube video, it seems to be running just fine. When I pulled all of the plugs they all looked good except for one. It was wet and my first suspicion of the day that there might be a problem. I'll go ahead and buy all new plugs and the carb is definitely jacked up so it won't fire up. I can't tell for sure, but I think the float has disinegrated. It just spits gas out of the little overflow vent hole.

I'm going to run down there today and pull that carb off to see if I can get it serviced before the weekend.

Thanks for the help guys, I'll let you know how it works out.