33EL69 1 cylinder has spark

[33el69]

I have a 33hp 1969, that is having an issue with the spark on one of the cylinders. There is a black wire that is hanging by the vacuum switch, and when it is left alone there is yellow/weak sporadic spark. When I connect it to the vacuum switch, it stops all spark on the bottom cylinder. The top cylinder has spark 24/7 and its strong. I cant find a wiring diagram anywhere, Replaced the coil thinking it could be that, but no change. Thank you for any help!

 

[timguy]

Could be a couple problems here. Sorry you didnt get a sooner response. That vacuum operated switch is there to protect against over revving, say in case of a broken shear pin. Vacuum shoots up and spark to that cylinder is immediately shorted to ground. So when you install that wire to the vacuum module and you completely lose spark on lower cylinder, then you have a problem with the vacuum module. If you keep that wire disconnected it should allow normal spark for the lower cylinder. So if you've changed the ignition coil and no improvement then I would look at the points for pitting, or possibly but not very likely a bad condenser, lastly a plug wire shorting to ground. Occasionally they can have abrasion or simply start arcing through one of the clamps that hold the wires tight under the starter plate. Also check the spark plug boot and make sure there is no rust or deterioration where it attaches to the end of the wire. And of course coil is set to the innermost edge of the bevel at the top of the mounting posts.