PLEASE HELP! Going Outta My Gourd!

[WhalerSailor]

Cheers... I have a 1979 70hp 3cylinder Merc with stator, trigger, rectifier, 3coils - no points. The plugs fire hot and blue and in time when out of the motor, but when replaced in the motor - no fire (checked with a timing light). The battery is hot and spins the starter fast. Someone suggested disconnect the rectifier and see if it fires. Did that - same scenario. All wires are good with no spark jumping. I don't know how to check the stator or trigger - only have a volt/ohm meter. Can someone help? I'm completely baffled.

UPDATE:
I just put on a new trigger to no avail. I did do a new test... Left all plugs in (none firing), pulled the wire off of the top plug and attached it to a grounded 4th plug. THE OUT PLUG FIRES! Still no plugs fire when installed (Checked with timing light). What the #*!@## is going on?

 

[Bifflefan]

Re: PLEASE HELP! Going Outta My Gourd!

Thats a real head scratcher...If all you say is true. (not to say its not)
Have you tried a different set of plugs??
I have never heard of a plug that will fire when not installed and grounded. and then not fire when installed.
I would consider taking that one in to a certified mechanic.

 

[WhalerSailor]

Re: PLEASE HELP! Going Outta My Gourd!

Thanks for the response bifflefan. I've never seen anything like this. It HAS to be a grounding problem I agree. I'm going to try some left hand experimentation today even if I have to strap a separate ground to each plug.

 

[RaScLeS]

Re: PLEASE HELP! Going Outta My Gourd!

how long have you had the 70 for ? i havent even been able to get on the water with mine damn thing wont rip it cause of a weak power pack im thinking

 

[hank55]

Re: PLEASE HELP! Going Outta My Gourd!

just a way out guess

I think plugs come with a short threaded area and a long threaded area, if your motor needs the long type, but your using the short type, maybe the spark is jumping over to the head.

I dont even know if thats possible

 

[j_martin]

Re: PLEASE HELP! Going Outta My Gourd!

Get a spark gap tester. A spark plug can fire when in free air, and fail to fire under compression if the voltage is not high enough. If it fires across a wide gap, it'll have enough voltage to fire a plug under compression, Also weak wiring can work in free air, and fail when put under the stress of higher voltage under compression.


The stator can be roughly checked out with a good ohmmeter.

hope it helps
John

 

[WhalerSailor]

Re: PLEASE HELP! Going Outta My Gourd!

Thanks again everybody. Just found something new.... I found that if I cross the plug wires (ex: put the #1 plug wire on the #2 plug) everything fires. Which means it just isn't firing under compression. Stator maybe? How can I check the stator?