1963 40 hp Johnson, won't start, just cranks over and backfires

[Taunce]

I just purchased a boat that came with a 1963 Johnson 40hp seahorse motor. I tried to start it the other day and here's what happened: I have the motor on a stand and the lower end unit submerged in a large container of water. I connected the gas tank and primed the bulb until tight. I hooked up the electrical to a car battery for temporary use. I turned the key and the engine cranked over but would not start. After trying again it cranked over and started and sounded good, the exhaust was stirring up the water and it sounded smooth, but I did not see any water come out from the spout. It stayed on about 10 seconds and stopped. Upon trying to restart it, the engine will crank a bit then a big bang out of the exhaust with a huge water splash is what happens now, along with a cloud of what seems to be clear/white smoke or steam rising out of the water in the container. The water had quite a bit of black oil in there also which did not appear to be leaking from the prop case but from the exhaust. I checked the spark which seems ok and the fuel seems to be getting to the engine also, but I am not 100% sure of that. This motor probably had been sitting for a long time before I got it but I find it strange that it would run smooth for a bit and then that happens, instead of it not starting at all to begin with.<br /><br />Any Ideas of what it may be or where to start looking would be greatly appreciated. I did just buy the manual for it and it does not seem to have a general troubleshoting section where I can get any ideas for this problem. <br /><br />Thank You

 

[Paul Moir]

Re: 1963 40 hp Johnson, won't start, just cranks over and backfires

That is very strange. Usually a big ol backfire like that is a good sign you've got the plugs wires on the wrong plugs. I take it you didn't play with that between when it stalled and when you restarted?<br /><br />Is the armature plate (just beneath the flywheel) turning with the throttle smoothly? Is the spring on the linkage there/working right?

 

[JB]

Re: 1963 40 hp Johnson, won't start, just cranks over and backfires

You also might have a sheared flywheel key, Taunce. If the flywheel slips close to 180 degrees you end up firing the wrong plug, just as though you had switched the wires.<br /><br />Good luck, and welcome aboard.

 

[Taunce]

Re: 1963 40 hp Johnson, won't start, just cranks over and backfires

I did take the wires off the plugs and took the plugs out, but I put the wires back on the same way they came off. The front wire to the top plug, is that right? The throttle seems to be smooth along with all the connected parts.<br /><br />The flywheel key I am not sure of but I will check it. Is it possible for that to just be, or to just shear like that for no reason or is there a specific reason that it shears? And if so then why? And where is it located specifically? In other words where can I begin my search, in my manual, is it covered under the ignition or something else?<br /><br />I am new to outboards, but I have a moderate knowlegde of small engines and auto mechanics and I have owned an outboard motor once before for my 12' aluminum, 6 hp evinrude, but that motor was brand new and did not need any work, even though it was over 40 years old, amazing. The person I purchased it from did not use it more than once and stored it wrapped in plastic and on a stand indoors. Needless to say that the motor did not need any work at all and did not even have a scratch on it and it still had the factory grease on all the moving parts, which was still clean and white too, after all those years! Oh, And most importantly it started! And stayed on too!...LOL<br /><br />I Thank You very much for your help and your welcome that you extended to me. I greatly appreciate it. I will check this out and get back to you to let you know what happened.<br /><br />Thank Again.

 

[BoatBuoy]

Re: 1963 40 hp Johnson, won't start, just cranks over and backfires

The flywheel key is in a keyway groove in the top part of the crankshaft and mates with a keyway groove in the center hole in the flywheel - no different than the small engines you're used to. If the flywheel nut is not properly torqued, it will shear the key.

 

[Paul Moir]

Re: 1963 40 hp Johnson, won't start, just cranks over and backfires

But in either case, it won't affect timing. Since the timing is ultimately derrived from a cam on the crank rather than magnets on the flywheel, a sheared key will only result in lost spark rather than bad timing. Unlike more modern outboards.<br /><br />The front coil's wire runs the top plug, that is correct. Lemmi sleep on it.