R1: Single carburetor on a 1978 35HP - noted. Difference between a real mechanic (R1) and a shadetree mechanic (me).
Just my thoughts. Based on what you describe, I would look at electrical connections and components in the ignition system.
You've swapped out coils, so it's not likely to be a coil.
Barnacles = saltwater, so corrosion is a possibility.
My thoughts on what it could be:
Electrical:
- The ignition module
- One of the pickups under the flywheel
- A corroded connection in one of the connectors
- A break in a wire
- I haven't experienced a situation where a spark plug wire lost its connection after running the engine for a while use, but this might be easy to check by swapping them out
I think that this type of heat soak electrical issue would occur after the electronics get hot. In some circumstances, this might not happen while idling around, but might show up after or during a higher-speed run. In other circumstances, this issue might show up after the electronics operate for a period of time. The way I understand this ignition system, it's powered by the engine's operation, not by the battery like on a car, so turning on the key (assuming it has one) without the engine running won't warm up the electronics.
Mechanical:
I'm still wondering about the head gasket. Could a blown head gasket or a cracked head on a 2-stroke show up only when the engine is hot? I asked about whether it sank hot or cold because I wondered about shock-cooling and warpage. This might show up as reduced compression when the engine is down to one cylinder, but that resolves itself at cooler operating temperatures.
- DW
