7 1/2 HP Johnson out board problem running

[JIM4475]

I have a 7 1/2 Hp Johnson not sure about the year but, it crank's within 4 or 5 pulls, but when I am running down the lake it will not run at WOT unless I hold the choke out just a little?? What do you guys think could be the most likely problem??
Thanks
Jim

 

[F_R]

Re: 7 1/2 HP Johnson out board problem running

How old is this 7.5? If it is an old one with adjustable high speed knob, give it a tweak toward "rich". If it is a newer one with no knob, the carburetor needs cleaning. The high speed fixed jet orfice plug is partially clogged.

 

[samo_ott]

Re: 7 1/2 HP Johnson out board problem running

Bang on. And if your carb has not been cleaned recently, it would be a good time to do it anyway!

And I tend to think it's a newer one as if it was from the 50's most folks preface it with "antique... or classic.... or old..."!

 

[JIM4475]

Re: 7 1/2 HP Johnson out board problem running

This one has the knob and I tried adjusting that also, it also gives a little trouble starting after it has been running for a while. It is most likely the carb it hasn't been cleaned in a few years. Should I buy a carb kit or just pull it and soak it with carb cleaner?
Thanks

 

[samo_ott]

Re: 7 1/2 HP Johnson out board problem running

If you're going to the trouble of pulling the carb off and taking it apart to clean it, buy a carb kit for under $20. It will make it nicer and easier to fix up. I find that usually it takes longer to re and re the carb then it does to actually clean it. I personally I would never do that much work if I didn't put a new kit in it as it's cheap insurance.

Post the model # if you can though so we know what you have. It's on a small plate on the transom mount.

 

[JIM4475]

Re: 7 1/2 HP Johnson out board problem running

The model # is J8RCSS.

 

[F_R]

Re: 7 1/2 HP Johnson out board problem running

That's a 1980. Clean the high speed orfice. It has to be absolutely positively clean. Nothing else will do.