Stumped! Need Advice. '75 Mercury 650 3 Cyl

[gholmesjr]

Here are the symptoms. Having a hard time timing the motor. It doesn't want to keep the timing it seems, it also seems like it is missing when idling. When it idles it surges. IF I can get the RPMs under 1000, it feels like it has a miss but often it will rise the RPMs on its own. Sometimes the motor will run away on its own and I have to shut it off. This doesn't matter if it is running in the barrel or on muffs. I am leaning towards a faulty trigger. I have a manual and the only test for the trigger is to test the black wire to the body of trigger for continuity. I get continuity on both the blue and the black wires coming from the trigger. When I run an Ohms test on the trigger I get 28.8 ohms from the black wire to the blue wire and the same when I run from the black wire to the body (ground). My manual doesn't have specific ohm numbers for the year of my motor, just that it needs to continuity I believe.

My next steps are to replace the spark plug wires as these are original wires. Anythings else I should be looking at or testing at this point? I hate to give up on this motor as I've put a lot of time and money into it, but at the same rate I've eliminated the easy items. I am hoping that someone here has an idea of where to look now.

So, here is what I have done so far:

Rebuilt the engine.
New power head seals all around, new top and bottom seals,
New thermostat, poppet valve,
Replaced water pump.
Replaced exhaust seal.
Changed plugs,
Carb kits, carbs rebuilt,
New main wiring,
Replaced distributor cap and plug wires (not new)
Replaced broken reeds,
Compression tested at 120 per cyl.,
Replaced all fuel lines,
Fuel filter replaced, fuel pump rebuilt,
Ohm tested stator vs. another stator, numbers are the same, continuity tested stator, tested good, no continuity between wires and body = good.
Took the switch box out and jumpered to check for spark through the switch box, got over a 1/2" jump with bright blue spark.
Getting spark to all three cylinders as tested with a timing light, but am not sure it is a good spark.

Thanks,

J.T.

 

[roscoe]

Surging tends to suggest fuel system.

Double check fuel pump diaphragm, and gaskets.
Double check carb settings and float height.
Check for air leak between carb and manifold.
Check all fuel lines for fit and tightness of clamps.

""It doesn't want to keep the timing it seems,""

So, is the timing not staying where you set it?

Check key and torque of flywheel.

Check all ground wires on coils.

 

[gholmesjr]

Last night I took the distributor off and manually lined up the rotor and the point and fired from the switch box through the distributor to the plug and got really good spark. It worked on all three spark plugs. I then hooked the trigger back up to the switch box, hooked power to the switch box and spun the rotor to see if the trigger would in fact trigger the shot of volts, it did not. Not sure if I grounded it correctly or if the trigger isn't working properly.

 

[gm280]

Last night I took the distributor off and manually lined up the rotor and the point and fired from the switch box through the distributor to the plug and got really good spark. It worked on all three spark plugs. I then hooked the trigger back up to the switch box, hooked power to the switch box and spun the rotor to see if the trigger would in fact trigger the shot of volts, it did not. Not sure if I grounded it correctly or if the trigger isn't working properly.

Sounds like you've figured out the problem. Check to verify you did ground it properly and if it still doesn't fire, time to replace... JMHO!

 

[gholmesjr]

Gm thanks for the reply. I ended up hooking everything back to the motor last night and trying with a key. No spark. So it was definitely grounded properly this way. I purchased another trigger assembly. Another $225.00 sucked into this boat that I haven't been able to use once since I got it in Feb.