1970 40HP Johnson: Running at 1/2 speed

[Jake12]

I bought this two week ago. Carburator was flooding out, would not idel smooth and would cut out after running for 10 or 15 minutes. I replaced the carb with a rebuild kit(float,needle and gaskets) and put in new plugs. Since then, I am able to get it to idel OK(after adjusting the the slow idel screw and putting in new packing) and dosn't miss a lick when running except that it will now only go about half speed. Runs and sounds good but it runs as though the engine is draging something. None of the linkage was messed with. Model # 40ESL 70A. Any suggesions?<br />Thanks,<br />Jake12

 

[Paul Moir]

Re: 1970 40HP Johnson: Running at 1/2 speed

A common failing for these engines is to loose spark under load. It's easy to test for the fault by doing a spark check. Start by seeing if you can draw a 1/4"-3/8" long spark off each plug wire. If it can only jump a very small gap, the problem is most likely a cracked ignition coil.<br /><br />New coils are cheap and replacing them is relatively easy with a couple 'special tools'. Nothing very expensive though.

 

[ED21]

Re: 1970 40HP Johnson: Running at 1/2 speed

Have you looked to make sure the butterfly valves are opening fully. Something could have been moved.

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

Originally posted by Ed:<br /> Have you looked to make sure the butterfly valves are opening fully. Something could have been moved.

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

Yes fully open. Thank you.

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

If I originally had a spark plug gap of.035 and now I have the gap at .030(the correct gap), do you think this could have been the problem and now it should run at full speed?<br />Thanks for any answers in advance.<br />Jake

 

[Paul Moir]

Re: 1970 40HP Johnson: Running at 1/2 speed

Not very likely, but could be. Run that spark check.

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

Thanks Paul for following me. I was going to test this evening but a storm is currently overhead. It's a kicked back evening.<br />Thanks a bunch.<br />Jake

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

Does the battery play a role in keeping the motor running? I have two battery's: one for trolling, lights,etc and the other for the starter only. The unit originally had a generator. No longer there. The battery always has enought charge to run the starter every time. With all this said and all notes from above, "If the generator is not charging the battery, would this be a cause of the motor only running at 1/2 speed or seems to be pulling a load? From what I am reading, I believe the magneto flywheel is what keeps the engine running but not sure. <br />Thanks,<br />Jake

 

[Paul Moir]

Re: 1970 40HP Johnson: Running at 1/2 speed

No it doesn't. The battery operates the starter, and draws from the generator. Other than that, it doesn't do anything for the engine.<br />The ignition system (a magneto) is totally independant from the battery system. You can disconnect the generator, wind a rope around the flywheel, and start the outboard without any battery at all.

 

[stan_deezy]

Re: 1970 40HP Johnson: Running at 1/2 speed

Jake, I'd listen to Paul for two reasons:<br /><br />1. He's pretty clever about these engines <br /><br />2. Sounds absolutely identical to the problem I had with a '73 25HP Evinrude and on checking it out the problem was a cracked coil: easy and cheap fix and a very smooth engine again.

 

[Jake12]

Re: 1970 40HP Johnson: Running at 1/2 speed

Ok. Before I pull the fly wheel, I want to check with you all about one more thing. At the begining of my project during the carb rebuild, I did not adjust the float to the horizional position(of course I found this out after the fact). The new float, seat and needle fixed the original problem: gas flooding out the front of the carb. Now...the question: Would this adjustment in the float be a cridical adjustment and the cause for running at 1/2 speed?<br />Thanks for all you help. This has been fun for me. I have a garage and all winter to get ready.<br />Jake

 

[Paul Moir]

Re: 1970 40HP Johnson: Running at 1/2 speed

The float adjustment is critical and can certainly cause bad high speed running & sever engine damage if set too low. It should be set so when the carb is held upside down, the float is level with the surface that the bowl gasket sits on.<br />The spark gap test shows cracked igniton coils almost perfectly.