No spark when plug is installed - Yamaha G1

[jimw]

Hello,

I have a 1982 Yamaha G1 golf cart that was working, but not running now. After some extensive trouble shooting I've narrowed down the problem (I think).

I doesn't make sense to me, but I get spark when the spark plug is not installed. Its good spark that arcs at least 3/4". When the spark plug is installed, I don't get any spark. As a test, I left the spark plug out, depressed the gas pedal and got good spark. While the engine was trying to start, I placed my thumb over the spark plug hole and the spark disappears -- remove my thumb, and the spark comes back.

It's the strangest thing! Anyway, all I can think is somehow the engine recognizes when there is compression present or not, and creates a spark when appropriate???

Any help would be greatly appreciated.

Thanks!

[Flintrock]

That doesn't make any sense......

[BigBlockMan]

try running a wire from neg battery to engine block or ground.

[oxfordlawn]

possible grounding plug wire when routed to "installed" plug?? When moving wire to test with plug out and resting on something..bad part of wire is not being grounded anymore??? just a thought..dunno. I dont get the no spark with finger over hole thing. Did you try another plug in cylinder while watching spark on another plug not installed but hooked to wire?? check that plug wire carefully

[jimw]

Originally Posted by Flintrock

That doesn't make any sense......

That's exactly what I said, over and over...


I originally thought we were bending the plug wire in a different way when the plug was installed or out. But, I was surprised when I covered the opening with my thumb, and could turn the spark on and off.

[oxfordlawn]

cant wait to see the results of this one

[Flintrock]

Listen to Tom, try running another ground from neg post to engine or frame, only thing that makes sense. Hopefully the the thumb trick is coincidence?

[tonyton]

I've seen plugs that don't fire under compression but not with your thumb being under compression. Seriously, plugs will sometimes fire at atmospheric pressure and fail under compression, that is not the problem here. I would try a new plug...
The only thing I can relate to fire with compression, no fire without, is a bad crank bearing throwing the magneto out of it's normal path. That doesn't seem likely but that's the only component that would be affected by compression or crankshaft movement..Let's see if someone else has had a similar problem.

Welcome to the forum...You picked a good one to start with!

[jimw]

Originally Posted by oxfordlawn

possible grounding plug wire when routed to "installed" plug?? When moving wire to test with plug out and resting on something..bad part of wire is not being grounded anymore??? just a thought..dunno. I dont get the no spark with finger over hole thing. Did you try another plug in cylinder while watching spark on another plug not installed but hooked to wire?? check that plug wire carefully

We used multiple grounding methods -- wire from battery, plug laying near engine block, wire from block, spark plug socket wrench (with and without plug underneath). Also, tried a new plug. But with the "thumb test" the plug and wire was stationary, and I could turn the spark on and off.

Only thing I could think of...

Does the engine have some sort of switch mechanism to turn off spark (and gas) to use the engine compression for braking purposes (with gas pedal slightly depressed)? (kinda far-fetched of an idea)

Does the engine crank/spin better with no compression. So, I get spark at higher revs, but not at lower revs?

[krimepays]

Check your coil pack it might be shorting to the head when I take my plug out I can see the spark coming off the coil pack and as soon as I put the plug in and start it it goes away.but there is also a a rubber grommet keeping it from grounding straight to the head...just my 2 cents!