I have a 75hp 1994 mercury it will not start ones it hits operating temperature

[Prem]

Ha people if you can help l have a 75 mercury that has on spark when l try to start it after it is at operating temperature it has no spark when hot

 

[fastjeff]

Best guess? Bad switch box (unless it has those CDM or whatevers).

Jeff

 

[galamb]

If you can test in a controlled environment (and I mean you don't want to need a tow back to the dock) and you have a ohm or multi-meter, the next time it won't start you can test the continuity between the two wires coming from the stator.

The exact reading is not super important at this point, but if you have "no continuity" between the two stator leads (not the yellow pair the ones feeding your switchbox) then you have a crack in the stator (one or more of the windings) that are expanding when hot and losing the ability to create power.

If the continuity is "good" (minimal resistance) then the issue is probably the switchbox but before chucking the money for a "swap and see" it would be worth having a shop run some dva tests to make sure the other components are fine.

1994 saw the ignition system change on these part way through the model year so posting a serial number will help anyone else that has ideas to know which ignition system you have - they are quite different from one another and each may have their own "quirks".

 

[Canufixit]

Check to be sure the magnets on the flywheel are good and strong when cold and hot. (Don't ask me why :')