Hi all! I have a friend with a tournament ski boat who is having trouble. Here's his story:

"It’s an 88 Sanger Comp Ski Boat 21’ with a 351 PCM engine.

The tach is reading double while idling nicely and runs smooth up to around 4000 (2000) when the engine starts to sputter and cut-out. We put in new points, cap, plugs, coil, fuel filter, fuel, oil filter and oil.  I checked the voltage on the shunt resistor and it was 4v, so the coil’s running about 9.  I just ripped the carb out to give it a good cleaning.  It’s a Holly 4bbl single pump with vacuum actuated secondaries.  The actuator had a split diaphragm, so it wasn’t working, but it’s rare that we get to that point, and gagging way before that.  I gave the carb to a repair shop. I’ll have the carb back in this weekend to see if that clears things up, but it still seems electrical to me."

Do any of you have opinions on what the tach reading 2X might indicate? This is not a situation where he changed the tach settings or bought a new tach - it just up and started reading 2 times higher. Thanks for any suggestions!

Sounds like you may have forgotten to put the proper spring in the points, sometimes the points have a removeable spring and I have seen this spring either installed incorrectly or not at all, it causes the points to bounce at anything above about 1600-1700 rpm but will idle and sound OK, that would be where I would start....

You can try disconnecting the grey tach wire from the coil on the engine to see if that is where your issue is, but I doubt it seriously, I think they are related.

Good luck!

GT

Nice work GT!
I will bow out to an excellent answer. 

Thank you!

Once and a while I can pull one out of my ass, curious to see what he finds now...

GT

Hey Steve,

Updates? 

GT

Nothing yet. He'll let me know once he solves it.

As usual, GT gets the prize! 
Here is what he wrote:

"Well that worked!   The spring for the points was with the parts we didn’t install!   After rebuilding the carb on Saturday, I put the spring in, set the gap, and fired it up.   No more doubled tach reading, and it ran up to  4K just as smooth as ever.
Today is the wet test.  We are heading to the lake as I type…
Thanks!"

GT, which bank account do you want the gold bullion deposited in?

Steve

Thanks for the update Steve, you are very welcome!

Proof positive, even a stopped clock is right twice a day 

GT