8 hp Johnson isn't getting much power

[Beek14]

I've got a 1990 8 hp Johnson that I've been playing with, and I can't seem to get much power out of it at full throttle. It will idle great with no problems. It will also rev up really high when in neutral too, but when in gear, it isn't seeming to go like it should, almost like a bog, but it's not like a typical bog. It just doesn't seem to want to go too hard. If I play with it, it gets a little power and seems like it's going where it should be, but then it gets under load and loses its power. I'm puzzled because it will rev up in neutral and stay high revving with no problems, but not in gear. Any ideas?

 

[iwombat]

Re: 8 hp Johnson isn't getting much power

Sounds like a dirty carb to me. Time for a kit and a rebuild.

But, compression and spark check first before ordering parts.

 

[Rick.]

Re: 8 hp Johnson isn't getting much power

Agee with above. You could well be running on one cylinder. It will idle fine and rev. fine but won't be able to deliver the horsepower your used to getting. When it is running poorly, pull a plug wire. If it stalls, that is the plug getting spark. If it makes no difference, that plug may well be dead. Do the same to the other plug and you will know which, if any, is bad. Best of luck. Rick.

 

[Beek14]

Re: 8 hp Johnson isn't getting much power

Hmm.. Good point. I hadn't thought of that. I'll get back to you guys after a few tests.

 

[Bugman1]

Re: 8 hp Johnson isn't getting much power

Agee with above. You could well be running on one cylinder. It will idle fine and rev. fine but won't be able to deliver the horsepower your used to getting. When it is running poorly, pull a plug wire. If it stalls, that is the plug getting spark. If it makes no difference, that plug may well be dead. Do the same to the other plug and you will know which, if any, is bad. Best of luck. Rick.

Rick, it's an 8(eight) horspower motor, how many cylinders and plugwires do you think it has? I am pretty sure it is only running on one cylinder. ,

Bug.

 

[Rick.]

Re: 8 hp Johnson isn't getting much power

Bugman1: Not sure what your getting at but a 1990, eight horse has two cylinders. Sorry if my post was confusing. Rick.

 

[crxess]

Re: 8 hp Johnson isn't getting much power

Compression test
Plug test under load
Pinch test fuel line under load

Has this motor always run this way on this boat? Wrong prop for application?

I have undergone this problem on my 6hp and done all the typical test. All passed so far, with the exception of unknown prop vs. application. Awaiting arrival of a new lower pitch prop to reduce load on motor before proceeding with further testing.

 

[Beek14]

Re: 8 hp Johnson isn't getting much power

Compression test
Plug test under load
Pinch test fuel line under load

Has this motor always run this way on this boat? Wrong prop for application?

I have undergone this problem on my 6hp and done all the typical test. All passed so far, with the exception of unknown prop vs. application. Awaiting arrival of a new lower pitch prop to reduce load on motor before proceeding with further testing.

Also a good point. It definately is a two cylinder by the way.. haha.. I am working on it for a buddy of mine so I don't know much about it. He also got it from a friend so he hasn't used it much yet either. So don't know much about the previous information, but I suppose that could be a possibility.