Boat Problem

[theboner]

Well as some of you know I bought a 1979 Chrysler tri-hull the other day.
It has a 1978/79 mercury 90hp motor on it.

It was running fine the first 3 or 4 times I have had it out then all of a sudden it now decides to start stalling. It will idle just fine and will allow me to throttle it up for a little bit then dies.

I know I have good compression as the boat wouldn't start and idle good without it. I also know it has a good spark as it is starting as well and idles

I have my concerns with vapor lock because of the damn ethonal in gas these days..... I am currently using 89 octane the same as when I had it out the 3 or 4 past times wihtout any issues.

Could it be
1. Vapor lock
2. Need to clean carb
3. To rich of a mixture
4. Some problem I am not aware of

I am probably going to run an octane booster to see if it will fix the problem that and change the plugs but if any one else has any other ideas I would be highly grateful

[ktmrider530]

How high does it idol before it dies? When it dies, does it shake? Does the engine smoke at all? And does it use oil at all? Pull your spark plug, and look at the tip of it for problems, if you're not sure what you're looking at, feel free to post a picture, i will be glad to assist you in this.

[theboner]

I am not sure of the Rpms as it does not have a tach. The engine does not smoke any more then it should(only smoke that comes out is from the prop as it should and it stops after about a minute of running)
The sparkplug is in good condition with some black on it but that is because its burning a gas/oil mix. The motor really doesn't shake before it dies. I just bogs down to a low rpm then it can't recover.

[ktmrider530]

Oh, it's a two stroke engine? On an outboard motor. I understand now. I'll ask some people and let you know.

[theboner]

Ok thanks ahead of time

[ktmrider530]

I haven't been able to get much information on this, since two stroke engines don't use intake or exhaust valves like a four stroke does, I'm not positive what the problem could be. My guess is that there may be a problem. With the reed valves, not allowing your engine to get fuel. Before it dies, does it sound like its out of gas?

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Upon doing a little more research, are you sure its a two stroke? Merc from what I can tell usually sticks with fours. Anywho, it could be it's carb idle adjustment jets, or bad compression, caused by a head gasket problem, honestly it would be hard to tell without seeing the engine.

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Upon doing a little more research, are you sure its a two stroke? Merc from what I can tell usually sticks with fours. Anywho, it could be it's carb idle adjustment jets, or bad compression, caused by a head gasket problem, honestly it would be hard to tell without seeing the engine.

[theboner]

I am sure its a 2 stroke as in 1979 the only models for mercury motors were 2 strokes, Also mine is a 1979 90hp inline 6 with 3 carbs. I am in the process of cleaning out the carbs and will disconnect the fuel lines and hook them up to my compressor to blow out any junk that may be in there.
From what I have been reading the problem is most likely due to the fact that todays gas contains ethenol which has a lower btu per hour rating about 20 percent lower to be honest. So it stops some of the gas from being burnedfully and causes things to varnish faster.

The other problem is also due partialy to the ethenol is vapor lock


But I get a new starter put on tommorow and I will once again test it on my lake to see if all is well'

Thanks for the help if you can think of anything else I would always appreaciate it.

[ktmrider530]

I don't believe that it's the ethenol in the fuel causing it. But i dunno. I'm sorry i couldn't help more. If i think of anything. i'll let you know.

[theboner]

It would be part of the main problem I believe. But after I run the octane booster the carb cleaner I will see how it does. I also need to borrow my friends compression checker to see if its over 100.

[ktmrider530]

It would be part of the main problem I believe. But after I run the octane booster the carb cleaner I will see how it does. I also need to borrow my friends compression checker to see if its over 100.

Make sure you pull all of the spark plugs when you do your test.