Slow Power Loss a Mystery

[RayB]

I have a 50’s era K engine in a 17’ CC Runabout. The engine starts, idles, and runs well. However, after 20 minutes of cruising at 3000 rpms, the engine speed slowly starts to decline. It will drop smoothly from 3000 to zero, over the course of 10-15 seconds, (not a hiccup or misfire) then stop and won’t restart. I have a virtually new ignition system, all new: coil (Flamethrower 3.0 amps), Petronix igniter, distributor cap, rotor, spark plug cables, and plugs. The coil is not overheating and reads about 94 degrees when the power loss starts. The distributor has no knock or vibration. The ammeter reading is normal, the oil pressure is normal as is the oil level, with no dipstick loss or hot oil fumes when running. The fuel pump is fairly new and squirts gas into a bottle when the output line is diverted. The sediment bowl is full and clear. I disconnected the water-cooling bypass a while ago, as the thermostat was unreliable, with no consequences. The engine now runs about 110 degrees while at 3000 rpms and remains at that temperature during the power loss. There is water coming out the exhaust pipe, and the block is cool enough to put your hand on it while it is running, and after it has stopped.

After 20 minutes of running, (you can set your watch by it) I am thinking that something is overheating, but with a cool block and no smoke or fumes, I am stumped. If this issue is covered in another post, please redirect me, thanks.

[Captain Nemo]

Hi Ray, Seems like you have been pretty thorough with your diagnostics. One thing that might be suspect is the pertronics unit, you might want to swap that out with traditional points. Might be worth a try?

[drrot]

Hi Ray, Seems like you have been pretty thorough with your diagnostics. One thing that might be suspect is the pertronics unit, you might want to swap that out with traditional points. Might be worth a try?

Sounds like a good place to start. Points and the original coil.