KA troubles

It was a frustrating weekend…my sons KA would not start, plug check showed no spark. New plug was no help, turned out to be a bad coil.

Question 1 - do coils just fail?

During the feature we had to do a restart after a turn 1 incident. On the restart his kart would not go, with the wheels off the ground it would run but as soon as it was back on the ground nothing just bogs and stalls. After the race we again ran it on the stand and it runs fine but under any load nothing. Double checked carb settings and they are both at 1 turn out (it was freshly rebuilt the week before). What is strange to me is on the stand it doesn’t act loaded up at all. Any ideas?

I’m not an expert on coils and electrical systems, but short answer is Yes, coils do fail from time to time.

You might check the ignition wire connection to the coil and to the plug boot. Couldn’t hurt to completely disassemble and clean the carb just in case.

We had a similar issues which were carb based. Leaking welch plugs if I recall correctly.

Coils do just fail sometimes, yes. Spark plug boot and wire also can go bad. Stators too, but you would probably notice as it’ll start to run rough when that happens usually.

Check to make sure you don’t have a carb needle stuck open or something. Sometimes the spring gets weak over time and the needle will vibrate itself open and dump fuel into the engine. Might need to put new needles in. Is there fuel in the air box? Sounds like it’s just dumping fuel and loading up. I assume the plug looks wet.

The carb was completely disassembled, ultrasonically cleaned and rebuilt last week.

I also tried a new boot assembly but still no spark.

Todd how did you determine this? Was the welsh plug visably disturbed?

Robert, after having the same issues you had, we sent the carb off to a karting / carb guru. His feedback was it was the welch plugs and it was not an uncommon problem.
It fixed the issue.
Note: We’d previously tried most of the other suggestions.

I don’t have my KA motor handy. Where is the welch plug located on a Tilllotson HW-33A carb?

KA coils have a tendency of just failing, one session they work fine the next they don’t, not super common but certainly not unheard of.

I personally have been running KA sense it first come out in Australia and have only had 1 fail in 6 years now

Double check that you didn’t mixup/swap the high and low jets when you rebuilt the carb as they’re different.

The kill switch buttons on the wiring harness have been known to go bad at times too causing electrical or running issues when things start vibrating on track. My builder recommended disabling mine to avoid those gremlins.

Chris I have etched an H and L in the needles just to avoid that and currently, all the wiring is removed just to eliminate variables.

I removed the carb and reeds and there was excess gas trapped by the reeds. I turned the motor on its side to allow any fuel in the case and there were a few drops. Reassembled and ran it with the same issue, under load it chokes and either stalls or just won’t rev. I believe it is getting too much fuel, why I don’t know. Going to try swapping carbs next.

The behavior of running on the stand, but not under load in my experience is a lean condition. If you run a fuel filter check/replace it, and check the screen under the white top of the carb. Also make sure that white top is tight and making a good seal as you don’t want it leaking any air.