'76 Johnson Air Supply Problem?

[tomwassmer]

I thought the most recent thread before this one was going to answer my question for me but it didn't. I was also wondering were the engine got it's air from. I am trying to tune up my 35 hp Johnson. I have noticed a direct correlation between my engine idling well and the cover off and a bad idle leading to a stall with the cover on. It's so obvious that I can stand there while it's idling well and place the cover on and it instantly runs bad. If I take it back off before it stalls, it immediately recovers and runs well. Any ideas? It may also help to note that the engine runs great (other than maybe a slight reduction in power with the cover on) at any power setting above idle.

 

[F_R]

Re: '76 Johnson Air Supply Problem?

Exhaust is leaking in under the cover and the engine is breathing it. Exhaust is low on oxygen which the motor needs for combustion. Can't tell you offhand where the leak is.

 

[ezmobee]

Re: '76 Johnson Air Supply Problem?

I hate to hijack the thread but I have always wondered, where exactly does the fresh air come from on an outboard like mine?

 

[ezeke]

Re: '76 Johnson Air Supply Problem?

It is probable that either you have the cover latches too close to the ignition wiring or you have exhaust gases leaking into the engine housing.

 

[tomwassmer]

Re: '76 Johnson Air Supply Problem?

Thanks for the help. I'm trying to track down the exhaust leak as we speak. I know I have water coming into the engine case from somewhere below the engine block and I'm guessing there is exhaust coming through with it. I can't figure out where it coming from without taking it all apart. Any ideas? Is there some kind of seal just below the engine block that if it had gone bad water would come through?

 

[iwombat]

Re: '76 Johnson Air Supply Problem?

Your water problem may just be a leaky water tube. Probably need a new o-ring. The two problems are likely unrelated, but in the same general vicinity.

 

[Chinewalker]

Re: '76 Johnson Air Supply Problem?

A leaky water tube would not result in water entering the lower cowling. It would have to be coming from the exhaust cover plate gasket, head gasket, or base gasket. Exhaust cover plate or base gasket could also account for the running issue - so they are most likely related...
- Scott

 

[iwombat]

Re: '76 Johnson Air Supply Problem?

*slaps palm on forehead*

Duh!

A far better answer.

 

[tomwassmer]

Re: '76 Johnson Air Supply Problem?

Thanks. I took the power head off the upper cowling (I think that's what it's called) and my base gasket is definitely bad. I can see about a 1 inch area where the exhaust was leaking through. I am trying to order the new gasket through iBoats and I'm having some trouble. Where can I find the OEM # for the part? It's a 1976 35 horse Johnson. I do not have the model and serial number off hand.

 

[F_R]

Re: '76 Johnson Air Supply Problem?

Thanks for reporting back. This is how we know if we got it right.

The parts book is available on-line at http://epc.brp.com/default.aspx?brands=ej&lang=E

 

[tomwassmer]

Re: '76 Johnson Air Supply Problem?

Thank you for all the help. I got the gasket, installed it, and now it's running great!