78 Tower of Power mercury 900 keeps diying

Joined
May 19, 2017
Messages
11
I got a 1978 Mercury 900 Tower of power a while back and had no spark issues. I fond out that the Switch was bad. I got a new switch and it ran like a charm for about 2 weeks. then one afternoon on plane the engine died. and would not start and stay running. it will start and it idles way ruff. and if I can get it to rev up with out putting it in gear it will smooth out and stay running. but soon as I drop the RPM's or try to up it in gear it dies instantly.

​ I took the distributor cap off and check to rotor it had a very little green build up of copper on one side and the connections in the cap were slightly white. I used a fine grit sand paper and shined them up. I check the trigger and it got 145.5 ohms. the Stator wires are kind of in poor shape plastic coating is falling off and the out side of the wires is a dull brown. I cleaned them up and put new leads in the best I could. and still no change. I checked the spark with a test light. cylinder 2 and 6 are bight a consistent. and all the rest of the cylinders have a weak or a inconsistent spark. also took the fuel pump apart and there is a very very very small hole in the diaphragm. could It be a fuel problem?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Sounds like you have multiple issues. Rebuild the fuel pump. Those fuel pumps are marginal, so they need to be in good shape.

Check the spark plug wires with your ohmmeter. Ohms should be zero, as wires are stranded stainless steel conductor. You maybe able to replace the boot and spring connector, cut them a bit shorter to get rid of the corroded parts.

Check the rest of the wiring harness. You need good voltage to the switchbox on both the red and adjacent white wires.
 
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