Reply To: RD-17 bottom plug fouling – no high speed power

[Don]

Well, I guess you need to verify that loss of spark is the actual issue here. Using those neon inline testers or a timing light while the engine is attempting to run at a higher throttle setting to see if either of the cylinders is losing spark.. This test on the water is best done at dusk when the sun is going down so you can see the tester or light. .Have you changed the plugs? Just cuz they might be new doesn’t mean they are any good.
Let’s just say that one of the cylinders is losing spark, and it is the cylinder connected to the vacuum switch. I would simply remove the lead from the vacuum switch and tape it up so it doesn’t ground, then retest…If the engine runs on two cylinders now, then we need to check the entire vacuum switch circuit before condemning the vacuum switch itself. This system uses some delicate mercury switches in the throttle to keep the system from activating when the throttle is set up high…