1975 Johnson 115 rough idle, runs great at WOT

[tjatech]

Alright, so here is the backstory to my issue.

I have a 1975 Johnson 115 on a 75 Reinell. Last summer, I was running the boat at WOT (at that point, motor ran great at all RPM's), when it suddenly conked out on me. I was towed back into shore, and diagnosed the issue as no spark. Since it was the end of boating season, I put the boat away without fixing it.

This spring, I installed a new power pack, all new coils, spark plugs, and rebuilt both carbs. Now the engine starts easily, but idles very rough (smokes like crazy too) and stalls out when I try to shift into gear. Once I do get it in gear, it coughs and coughs then suddenly cleans up. At WOT, the engine runs fantastic.

Anyone had this issue? I am thinking my carbs might be out of adjustment, but not sure.

Thanks in advance.

 

[danoutbard]

Re: 1975 Johnson 115 rough idle, runs great at WOT

Might have a cylinder not firing. If one cyl is not firing, your gonna have a lot of unburnt gaz/oil at the exhaust.

Check spark with an air gap tester. A good spark should jump a 7/16 air gap.

 

[tjatech]

Re: 1975 Johnson 115 rough idle, runs great at WOT

Yeah, I do have a lot of unburnt gas and oil in exhaust. What would cause 1 cylinder to not fire?

 

[danoutbard]

Re: 1975 Johnson 115 rough idle, runs great at WOT

Many things could cause a cylinder not fire;

-Cross pluging ex: 1432 instead of 1234 ( happend to me, does fire but at the wrong time)
-Faulty electronic

Again check for spark and reverse cables

Good luck

 

[tjatech]

Re: 1975 Johnson 115 rough idle, runs great at WOT

Well, I guess I got lucky. Did a quick link and sync on the carbs and the idle cleaned right up. I also adjusted the cam follower to the proper position which fixed the coughing on acceleration.

I think the carbs got knocked out of adjustment during the rebuild.