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

[Don]

It just doesn’t make sense that a carb problem would affect just one cylinder on a single carburetor engine….
I know the plugs “look bad”, or at least one of them does, but is it running on two cylinders in gear at high speeds? Sounds like you are running it in a test tank only, do you have a test wheel, or are you running it with the prop? Trying to run that big engine in a tank with the prop while in gear is near impossible, it will just throw the water out of the tank and ventilate…So, if this is what you are doing, seems unlikely you are getting the high speed mixture correctly set. I think the best bet is to take it to the water this weekend….
Just for grins though, check how many turns the high speed needle is set out from gently seated now. If the needle is set a couple of turns out, then I am confident the test tank is confusing things and you will get the needles set properly once on the boat. Now, back to the nozzle gasket…Is this carburetor the exact replacement for the 1955 RD? Or is it from a newer engine that had two needle valves instead of a fixed high speed jet? The reason I ask is that many of the older carbs with an adjustable high speed needle did not use a nozzle gasket. The bowl nozzle tube fits pretty tight against the carb body boss, I guess there is so much fuel going through there, the little that might leak by is negligible. So, my concern is that adding a nozzle gasket where none is called for might either damage the nozzle gasket and have it fall apart….Or, perhaps the nozzle gasket might prevent the bowl for positioning properly on the body….I guess the only way to know is to pull the carb bowl and see how the nozzle gasket looks.
The vacuum cut out switch is wired into one set of points to kill spark to that cylinder if the engine “runs away” in neutral, which these engines had a tendency to do if over revved in neutral…The vacuum switch closes, kills spark to one cylinder, allowing the engine to settle down, the vacuum switch to open, then spark returns to that cylinder.
At this point, I think it is best to take the boat to the water to determine if it is running on two cylinders are high speed….This could just be a case of attempting to run and adjust this big engine in a tank, which is near impossible without a test wheel…