Mr Gadgets

Your ignition system supplies the signal to the tach. If power to the tach was a problem, the motor probably would not burp. I would look at power to the coil and ignition system. Look for lose wires, grounds, bad connectors etc. Get in the engine compartment while it is cold and familiarize your self with the wiring.. if you find something lose, tighten it, then if it happens again you know where to go while the engine is hot..

good luck.. keep us posted
Dick

garysol1

I would certinaly keep an eye around the coil area reason being you say it takes about 20 minutes for the problem to show up. The coil will heat up as you run where as the ign key/wiring really wont. Is it possible on this configuration to start the engine then run a jumper to the coil so you can run the boat and bypass everything else for troubleshooting?