50s 7.5 hp, problem staying running

[zig]

I have a 50s era Johnson 7.5 hp AD-11 motor. It starts fairly easy when cold. It will run at half throttle for a while, then seems like the throttle goes up and it dies. It usually starts up again, runs for a bit then dies. Once it is hot it doesn't like to start. I have a copy of the parts catalog and can order parts from a local store, but I don't want to start buying parts I don't really need... So any help with this would be greatly appreciated... I sprayed some carb cleaner down the carb before start up. The plugs look decent also.

 

[lindy46]

Re: 50s 7.5 hp, problem staying running

Sounds like a bad coil which is cutting out once it warms up. Probably only running on one cylinder at idle. Coils/spark is the first thing I would check.

 

[zig]

Re: 50s 7.5 hp, problem staying running

Thanks for the input. I was kind of wondering about that. It makes sense, because it starts to sound real bad and just kind of spurters to a halt...

 

[F_R]

Re: 50s 7.5 hp, problem staying running

Thanks for the input. I was kind of wondering about that. It makes sense, because it starts to sound real bad and just kind of spurters to a halt...

They are notorious for cracked coils.

 

[zig]

Re: 50s 7.5 hp, problem staying running

I could see through the hole in the flywheel they were discolored. I found a website that was selling them for a little under $30 a piece. Now the fun part of removing the flywheel... Need to go get a puller...