Hi revs and won't shut off

[Fifty]

Hello, everyone. Well I got my '67 Johnson 40 running yesterday and it started right up. The only problem was that it started revving pretty high immediately (I'd guess aroung 3,000 rpm). Then it wouldn't shut off and I had to dissconnect the fuel line. Maybe the throttle linkage is way off and the ignition switch is bad? Or could there be a single problem that would cause both of these symptoms? Also, the motor was throwing a lot of white smoke from the power head. Is this normal? I had put Marvel Mystery Oil in the cylinders a few weeks ago and maybe it was excessively smoking because of that? Thanks for your help, all.

 

[91cajun]

Re: Hi revs and won't shut off

When I have run marvel mystery oil through the fuel system it does cause the exhaust to put out white smoke. I've never put it directly in the cylinders. Where is the smoke coming out?

 

[jtexas]

Re: Hi revs and won't shut off

Sounds like "runaway" - happens when you give it too much throttle without the backpressure of being in the water. Tiny bits of carbon in the cylinders heat up and provide the ignition, so shutting off spark won't cut it off.

See if the throttle plates are closed off all the way. They should just open a little when you raise the high-idle lever. If that looks normal then start the engine but keep the revs down to just what you need to keep it running. Then if the key won't turn it off, the choke should stop it, and you can troubleshoot the ignition switch. Turning it to "off" should connect the black wire to the black/yellow.

 

[Fifty]

Re: Hi revs and won't shut off

I had the motor in a large garbage can but the propeller was probably only about 8 or 10 inches into the water. Is this to shallow. I kept the motor in neutral. Should it be put in gear to give it more back-pressure? I'm not supposed to start the motor in gear, right?