Does idle speed affect shift interrupt?

[cheburashka]

Finally got my '72 140hp to run well--Pertronix with power coming straight back from the ignition switch--so I was playing around with settings while out on the lake. I was able to drop the idle down to 750. Tooled around on the lake for awhile and when it came time to dock, I realized that I couldn't find neutral unless I shut down the motor. Sounds to me like the shift interrupt isn't working. I pulled the boat out of the lake and I'll check things out next time it's in the water, but I'm wondering if having too low an idle setting (or having a straight electrical connection back to the coil) can interfere with the shift interrupt.

 

[Bondo]

Re: Does idle speed affect shift interrupt?

but I'm wondering if having too low an idle setting (or having a straight electrical connection back to the coil) can interfere with the shift interrupt.

Ayuh,... You've got it at the High side of acceptable Idle now....
650/ 750 at idle In the water is what's called for...

I'd suspect the Wiring at the coil is the Problem....
The switch Grounds out the coil, causing the stumble...

 

[cheburashka]

Re: Does idle speed affect shift interrupt?

It's a Mercruiser 140 4-cylinder. The funny thing is, it always worked fine with a higher idle--back when it wouldn't idle lower than 1000-- and what seemed to cause the problem was dropping the idle down. I guess it could be the wiring, but I assumed that the shift interrupt switch only affected the negative side of the coil.

 

[Don S]

Re: Does idle speed affect shift interrupt?

Your shift interrupt switch should be hooked up to the negative terminal on the coil.
You can test the switch by starting the engine and manually engaging the switch and see if the engine dies.