Stator/Wiring Harness test questions

[vupilot]

1974 Merc 402 40hp Canada motor. I suspect a problem at either the stator, switchbox or wiring harness. The last 3 times out, after 10-15 minutes the motor started stumbling like the key being turned on and off after about 15 minutes of running. Those first 10-15 minutes everything works perfectly. This started with just a once in a while hicup one day and the next couple times out it does great for 10-15 minutes then stumble sharply like crazy at anything above 1/3 throttle but would idle back to the dock no problem. Last time out I adjusted idle mixture and installed a new throttle cam which I broke while tinkering. While on that test run we didnt even make it back to the dock but after 30 minutes the motor started up and ran great and I put it on the trailer in less than 5 minutes. That was all last fall, winterized and havent been back in the water since.

Question 1.
When I test the stator with the ohm check. Do I keep the wire (red) from the stator connected where it connects to another short red wire at the screw terminals which then goes to the switchbox? Or, do I need to disconnect the red stator wire at this screw? I believe I disconnect it to ohm test shouldnt I? For a volt test while running keep hooked up and test at the screw?
Also does this red wire test both the high speed and low speed windings of the stator? Or is there another way that is a more complete test of the stator with the other wire from the stator? Seloc says just test the red wire for this motor/stator.

Question 2. Testing the main wiring harness that plugs into the side of the motor. When ohm checked with the key "on" and the battery disconneted the center plug (7 hole plug) makes my ohm needle bounce around the scale. Whats this indicating? Could this be my problem or can this motor run without the harness hooked up.
Thanks, Im electron ignorant.

Im pretty sure this problem is electrical. I have new fuel, good vents, new fuel lines, new bulb and trying pumping it doesnt change engine speed at all. Compression was tested right before my problems and was said to be at 120 on both cyl but I did not test it myself. I have not removed carb.

Thanks

 

[vupilot]

Re: Stator/Wiring Harness test questions

Update:

I ran the motor today on the trailer, in the water at the ramp. After 15 minutes at just under half throttle it started spitting and sputtering like crazy. Checked the ohms on the trigger leads. They read right at 8.5 and should be 8-10. Started back up and made sure still running like crap above 1/3rd throttle and then checked ohm's on stator red lead and read 50, right where it should 50-60. Pulled off orange wire at switchbox and that made no change in running so must not be the kill circuit. Pulled off orange rectifier leads and that didnt make a change either. With this type IV thunderbolt ignition on a 1974 402 40hp will ohm checking the red and the dark (faded blue or black) colored stator leads show anything? It says on the manual start to check it that way buy my elec start says just ohm the red lead. I tried it anyway and it read nothing using both stator leads.

By this time I had run the motor an additional 10-15 minutes between all the checks and it continued to run worse each time until it would no longer start at all. It does this everytime now and after an hour it starts and runs fine again for 15 minutes.

So do you guys think its the switchbox since my stator and trigger checkout OK? How can I be sure before I spend the big bucks for a CDI replacement?

Thanks.

 

[vupilot]

Re: Stator/Wiring Harness test questions

Turns out there was some RTV in my carb bowl and the Primer Bulb was bad. Thanks for all the help.