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1976 Merc 850 no spark on 3 amp 4

F

fojtik

New member
"I was at the lake going about

"I was at the lake going about 30 mph when the engine just rolled back to a rough idle and then stalled. It re-started by ran VERY rough and would only run at slow speeds. I had no choice but to run it for about 10 miles in order to get back to the dock. When I got home I did the following: check compression-all about 120ish, check spark-good on 1&2 but nothing on 3&4. I tested the trigger and it passed. I tested the stator and it passed. What else could cause me to lose spark on 3&4???

Thanks for your help"
 
"That makes sense. Is there a

"That makes sense. Is there any chance the stator could be bad but test good on the ohmmeter? The wires on the stator are crap. I've taped them up but was thinking that must be the problem. Is it common for the switchbox to go bad? I hate to spend $200 - anyone got an extra one laying around?

Thanks,"
 
it is possible for the stator

it is possible for the stator to test bad with a OHMS test an output test with a DVA would show a bad stator. a switch box is a very common problem but they cost around 400 bucks you would have to test it with a DVA. check all of your grounds and battery connections. i dont have an extra switch box but ask around at scrap dealers
 
Is there any way the mercury s

Is there any way the mercury switch could cause loss of spark to only 2 of 4 cylinders? What should happen if I were to disconnect the orange wire that goes from the mercury switch to the switch box? I'm having a hard time understanding how that switch works. I've read the manual several times. Is the orange wire hot when the key is on but then when the key is turned off it provides a ground which grounds out ignition?
 
"Yes, the stators do that. I u

"Yes, the stators do that. I usually wind up replacing both at the same time. Almost always.

The mercury switch will stop the spark on all cylinders if the motor it tilted up.

THERE SHOULD NEVER BE POWER ON THAT WIRE FOR THE IGN KILL ON THIS MOTOR. THAT WILL BLOW THE BOX UP. THE IGN SWITCH MAKES CONTACT TO GROUND ONLY TO STOP THE MOTOR."
 
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