Problem Going Back To Neutral

The following question was emailed to us by Robert,

I have an old starcraft (1977) cruiser with a MerC 233. Wonderful boat, but, when I'm on the water, It stalls when I go from "in gear" to neutral. (same response if I'm in forward or reverse, but I've managed to keep it running from forward if I move fast enough, and hit neutral dead on) This makes it really hard to "dock" the boat. When I am in the driveway and running on earmuffs, I can go back and forth and have no problems with stalling.

Other boaters have told me to check my "shift interrupt switch" which I have located in the engine compartment. It doesn't make sense to me that it works fine in the driveway, but not on the water.

Furthermore, It looks like the shift interrupt switch has been made "no longer available" by mercury. Is there somewhere else I can get one? The metal strip that runs from the "switchbox" to the "roller" is not straight, and looks like it has been bent. Is this correct?

What are my options?

PS, your site is awesome, I was looking for a step by step to replace the impeller and your site was the best I found!!

Robert :

Our reply was :


The reason you can shift on your driveway is because there is no resistance against the clutch, located in the lower housing, which puts a strain on the shift cable that causes it to trip the interrupter switch. Take the prop off and at an idle, use a pair of leather gloves to put a drag on the propshaft and the problem will reappear as if you were back in the water.

Your interrupter switch is fine, the problem is either your lower shift cable is out of adjustment or needs to be replaced. 

At the engine, with your engine off, remove the end of the cable going from the engine to the outdrive and see if it slides in and out freely by hand. If it is sticky, replace the cable. If it moves easily, adjust the cable >