Will not run correctly until warm

[WVFisher]

I have a 1989 model Johnson 150hp. The motor just started this behavior this fall. The motor starts fine and idles. But when you try to get it on plane it dies or sputters like it is running on only a few cyls. This will happen for about 10 minutes at which time it will plane out and run as good as new. For the rest of the day no matter how long you fish on trolling motor and dont start it it will start and run perfect. Next morning, same thing. Have had it to a dealer and they checked it out and found nothing wrong except they say that some of the cylinders are losing compression. Strange that it will run 60mph after it warms up. This is as fast as it ever ran. Any ideas?

 

[oldcatamount]

Re: Will not run correctly until warm

Sound like a fuel delivery issue. You may have a small air leak in the fuel line which would lose the fuel prime over night and re-suck the prime the next morning. While it re-sucks, the motor will not run well until it's re-primed. Check for a loose clamp or a bad o-ring, cracked fuel line etc.

 

[WVFisher]

Re: Will not run correctly until warm

I forgot an important thing. If when it doesnt run well you remove the plugs they are covered in gas. If you then change the plugs the motor will run good.

 

[oldcatamount]

Re: Will not run correctly until warm

Are all of the plugs in the same condition when you remove them, or are there one or two that are dryer than the others?

 

[WVFisher]

Re: Will not run correctly until warm

I am pretty sure they are all wet with gas.

 

[James R]

Re: Will not run correctly until warm

Interesting.
Are you sure that it is gas and not water. Are you using a water trap filter in the fuel line?
With the crap ethanol mix fuel we have to buy a water trap filter is a must on the bigger engines.

 

[boobie]

Re: Will not run correctly until warm

Just for the heck of it, have you ever ran an open air gap spark test on
it before you start it? Spark should jump 7/16" gap. If that's okay I'd go along with possible water in the fuel.

 

[200GT]

Re: Will not run correctly until warm

I gave a 1990 200 GT with the same issue. Run rough adn wont get on plane but idle for a few minutes, then it will get up and go like nothing was wrong for the rest of the day. Next day, same thing. Did anyone ever find out what the exact problem was here?

 

[kenmyfam]

Re: Will not run correctly until warm

I gave a 1990 200 GT with the same issue. Run rough adn wont get on plane but idle for a few minutes, then it will get up and go like nothing was wrong for the rest of the day. Next day, same thing. Did anyone ever find out what the exact problem was here?

Calls for a basic health check of the motor to begin with in my opinion.
Compression
Spark
Fuel delivery
Spark plug condition.

Hard to begin any accurate diagnosis without the above.
Just my 2 cents though.

 

[Johndhii]

Re: Will not run correctly until warm

I have the same motor except in evinrude format, have you tried replacing the fuel water seperator?