'71 Starcraft 21'. I/0 Merc. Spark interrupter switch???

[Doboy]

Hi. The old girl has been sitting for a while. Time to pull her out, fire her up & see if the G-kids want to learn to tube & ski.
Dumped some gas down her throat 2-3 times, & she fired up & purred like brand new!
I had the lower unit in a drum of water, along the head phones on. After she warmed up I shifted into forward,, no problems. Back into neutral, then into reverse slowly,
SHE DIED!
Back into neutral & Crank crank crank. Dumped more gas in her just to see, & nothing.
NO SPARK. I think the plunger on the spark interrupter switch stuck????
Is that possible? Everything on the transom seems to be functioning properly.
Or, maybe the contacts on the inside of that switch are corroded?
Shouldn't those switches be totally water proof?

And lastly,,, would I be able to run a hot jumper wire from the battery to the positive side of the coil, & fire her up?
Where would I find that part number, & or replacement switch?

THANKS tons for any guidance!

 

[kenny nunez]

Your problem is in the upper gear housing where the shift slider travels for reverse. The switch is not the problem. There is a build up of crud in that area preventing the slider with just enough resistance to activate the switch. Jumping a wire from the battery will not help and end up burning the points up.
You might luck out by disconnecting the short cable that goes to the transom and with the engine running with a flush out try pulling and pushing the cable from forward to reverse which might clear the resistance.
If this does not work you will have to pull the drive to clean out the crud.
There are tutorials on this site to guide you through the repair.

 

[Doboy]

Your problem is in the upper gear housing where the shift slider travels for reverse. The switch is not the problem. There is a build up of crud in that area preventing the slider with just enough resistance to activate the switch. Jumping a wire from the battery will not help and end up burning the points up.
You might luck out by disconnecting the short cable that goes to the transom and with the engine running with a flush out try pulling and pushing the cable from forward to reverse which might clear the resistance.
If this does not work you will have to pull the drive to clean out the crud.
There are tutorials on this site to guide you through the repair.

Thank You, very much.
I'll try to find those tutorials,,,, & or maybe a Youtube video!?

We put an electrical tester on the coil, ran it to ground, & it read out +- 5 volt in forward & reverse, AND we were able to see the interrupter take it to zero when we were shifted into the bottom of that cam.
At that point, we knew that the interrupter was still functioning.
My younger friend decided to eliminate all of the old hard grease that was on the end of the shift cables,, around the lobes on that cam, & on the back side of the interrupter plunger. PB blaster, WD40 & small chunks of rags.
AFTER he 'cleaned' everything up, we tried the F & R shifting again. That's when we noticed that the coil was always energized. The interrupter would not cut off the juice, no matter how many times we cycled the shifter & cables.

Plunger out, roller into bottom of cam,,, Switch is running 12v juice to ground, right?
We made a phone video of the cables, cam & switch cycling,,, but I don't know how to post it here.

Next available day, we will pull her out of the barn again, supply it with water, fire her up & try to see what the hec happened. Hopefully.

Thanks again.

 

[Scott Danforth]

go to the top of the mercruiser forum, and look at the stickies.