Johnson 40hp Outboard

[datsunsrule]

Hi, I have a 1975 Johnson 40hp outboard that I can't get to idle correctly. I recently rebuilt the carburetor and did not see any improvement. I tried several main jet adjustments, and it idles fine for about 10 seconds, then you can hear the rpm slowly drop until the motor stops running. I did notice that there is a spot on the engine block below the carburetor which is supposed to have a vacuum line attached to it but doesn't. Can that affect the idle?

Also, I was thinking about throwing new coils and condensers on it, and replacing the fuel pump diaphragm. Does anyone have any other recommendations???

Thank you!

 

[Daviet]

Re: Johnson 40hp Outboard

Well, you need to start with some basic checks, compression and spark. The spark should jump a 7/16" gap and be bright blue. If the above checks out then you move on to the fuel delivery system.
I think the hose you are talking about is a oil return hose that goes to the upper part of the manifold.

 

[tashasdaddy]

Re: Johnson 40hp Outboard

the line is a recirculating hose that should connect to the back of the air silencer.

have the fuel lines been replace from carbs to tank, with alcohol resistant fuel line?

here are the PROPER adjustments.

http://forums.iboats.com/showthread.php?t=167352

 

[Rick.]

Re: Johnson 40hp Outboard

If it is missing a vacuum line that will certainly affect the idle. Have a look here and see if you can figure out what your missing. I wouldn't replace all those other parts just yet. Best of luck. Rick.

http://epc.brp.com/SiteMods/BRP_Public/BRP_Public_Login.aspx?ReturnUrl=/Index.aspx

 

[datsunsrule]

Re: Johnson 40hp Outboard

Thanks guys, I'll give it a try. The fuel lines are actually very old, and I need to check the spark.

 

[datsunsrule]

Re: Johnson 40hp Outboard

Also, I removed the electric choke mechanism. Could that affect the idle?

 

[Rick.]

Re: Johnson 40hp Outboard

Also, I removed the electric choke mechanism. Could that affect the idle?

Not sure why you would do that. Is it cold starting when your having the problem? Rick.

 

[datsunsrule]

Re: Johnson 40hp Outboard

Not sure why you would do that. Is it cold starting when your having the problem? Rick.

well, I'm not sure the electric choke is working properly because the choke has a tendency to rest in the closed position. I don't have an issue with cold starting, so I removed it to troubleshoot the rough idle.