1991 Club Car DS Gas - Interesting spark plug problem

[JoeBleaux]

Thought this this might save others some time, needless work and most importantly, frustration and help others having issues with a non-running or marginally-running cart. Also, if anyone has a service manual for this cart or just the engine - KF-82) they can email me, I'd greatly appreciate it.

The cart is a 1991 gas with the KF-82 engine. Very low total running hours - I'm the second owner and both the previous owner and I have only used it lightly around our properties and hunting camps. I don't think he ever had any issues with it and I haven't either. Just washing, oil changes, fuel filters and now, after a fair number of years (seriously), a new spark plug.

I'm a fair shadetree mechanic, but I've never seen this before. The cart ran fine last weekend and this weekend, it wouldn't start. I did all the typical checks - air box and filter were clean, fuel supply/pump working, it was getting spark as indicated by both a spark tester as well as the plug appeared to be producing a good blue-white spark when grounded to the engine. Did a compression test and it was around 100 PSI. Removed and cleaned the carburetor, which showed no signs of problems, and reinstalled. Still didn't start. Took off the head and everything was moving as expected and all looked surprisingly good (like I said, a "low-mileage cart," but since it was apart I cleaned what little carbon was there). Reinstalled it and no joy. WTF?

OK, I was pretty sure it wasn't fuel/carb issues - it was fresh non-eth and the pump was working with fuel in the carb bowl and a freshly-cleaned carb. I knew it wasn't compression or air flow. The only remaining thing was the plug itself. While I knew the coil was sending fire and the plug APPEARED to be producing a good, even spark...well, maybe... So I replaced the plug (an NGK 4626, which showed as a cross to the various BPM4A, BR4HS, etc.) and flock me, it started right up and ran! I even compared the sparks, at night, and I cannot tell a marked difference between them but yet with the old plug, no joy, and with the new one, get on it and go. If someone can explain this, I'd love to hear it, and hopefully, it may help others.

[Springbok]

Weird. At least it was an easy fix.

[mrgolf]

When the insulation on a plug cracks the plug will fail under compression. In aviation if you drop a plug once you must drop it again into the trash can, they cost 20.00 plus each. You can't pull over and change one at 10,000 feet.

[JoeBleaux]

Originally Posted by Springbok

Weird. At least it was an easy fix.

It was an easy fix...after I damned near rebuilt the engine I hadn't thought about the cracked insulation/compression failure theory, though...that may be the cause.

I know most of us don't like to simply throw parts at a problem until we stumble on to a fix, but I'm gonna be a little more willing to throw a new 2.00 plug at a similar situation should it ever arise again with any other small engine troubleshooting.

[JoeBleaux]

Originally Posted by mrgolf

When the insulation on a plug cracks the plug will fail under compression. In aviation if you drop a plug once you must drop it again into the trash can, they cost 20.00 plus each. You can't pull over and change one at 10,000 feet.

I think you are on to something, thanks.

[lockman1]

A hint of sarcasm maybe?

IF... by chance... it becomes intermittent again,
I've read about a few KF82 owners replaced the spark plug boot, and it solved their spark issues,
apparently, the connection between the boot and the wire breaks, and causes intermittent spark!
the boot IS a replaceable item, and it's inexpensive!

.02

[JoeBleaux]

Originally Posted by lockman1

A hint of sarcasm maybe?

IF... by chance... it becomes intermittent again,
I've read about a few KF82 owners replaced the spark plug boot, and it solved their spark issues,
apparently, the connection between the boot and the wire breaks, and causes intermittent spark!
the boot IS a replaceable item, and it's inexpensive!

.02

I guess anything is possible, but I examined the boot carefully and don't think that is related to the issue with this cart. This isn't intermittent - it follows the plugs: The old plug appears to produce a good spark yet no go, but replace with new plug with similar spark and away you go. Switch back to the old plug, and back to no go, switch yet again to the new plug, and it fires right up. There is something up with the plug and I think mrgolf is most likely correct. If he isn't, I'm not going to do a necropsy on it.

[Sergio]

The voltage required to create an arc across the gap under the air mixture compression is higher than the voltage when not under compression.

Typically You see a nice blue spark with the spark plug outside the cylinder if everything is correct, but without proper test equipment, there is no guarantee that spark will happen under compression.

I got burned once with that scenario, so now I just buy an extra spark plug anytime I get any small engine tool and use it to verify the spark plug is working.

[JoeBleaux]

UPDATE AND ANSWER - mrgolf nailed it. While I wasn't going to do much, I did look at the plug's tip under strong magnification and there it was - a hairline crack in the insulator at the tip - good call mrgolf and something I'll remember.

[mrgolf]

Glad that took care of the problem for you.