Hey guys quick question. We had a race on Saturday and my son was running fine all day, top 3. Come the finals we went through the same procedures as always warming up the kart, at the start his kart was completely dead, got destroyed and was dead last, would go past 11,000 rpms for the entire lap so he pulled off. Got the kart on the stand, started right up, sounded fine, pulled the carb and checked the reeds, they were perfect. Any suggustions? Just seems strange.
I tried a VLR at DKC and Mike had to drive it around in angry circles, whilst fiddling with the dials on the carb to get it to stop “4 stroking”. (It wasn’t revving out).
So frustrating, especially for my son. We didn’t touch anything all day, then bang runs like crap! Kind of hard to tell a 14 year to play with the carb on track.
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Being all of the sudden like that I’d suspect something like a stuck pop off in the carburetor. When it get’s stuck the carb goes super rich and runs like crap.
Reeds not seating, bad plug, loose reed cage to motor, loose carb, carb diaphragm, all of the above can cause what you describe…
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Could be electrical if it revs out on stand with zero load on it but starts stumbling under load.
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what’s the plug look like? Were you making carb adjustments throughout the day to keep up with weather? Sounds like it may have just loaded up on the out lap and he never got the thing fully cleaned out.
Not fun but part of the learning process and part of what he’s going to have to learn to successfully race 2-strokes is understanding carb behaviors and making adjustments on the fly to correct them.
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I wouldn’t think it would hit 11k if it was loaded up. That seems like an oddly high RPM. Typically it loads up on bottom end and then you just can’t get rolling from a stand still.
Part of racing an engine with adjustable carb needles is being able to adjust them on the fly if an issue like this arises. Then you could at least rule out fueling being one of the problems. At the risk of being the old man yelling at the clouds, when we were juniors (12 years old) in Komet, we all knew how to adjust the carb to lean it down for starts or make adjustments to hit correct EGTs during the race. It does take some learning and practice, but in my opinion is a vital skill to have in your back pocket these days when most kids can’t be bothered to learn it. Could save your race or net you a win someday if your driver can eek out a bit more performance by tweaking the needles. Could also save you an engine rebuild someday if he can prevent an engine seizure if for some reason the carb goes too lean on top.
As an exercise, sit on the grid, have him reach down and ask him to adjust the needle 1/4 of a turn. Then see where he ends up moving the needle and keep doing that until he gets a feel for what his fingers should be feeling for and how far he’s moving it.
Again though, having it run unloaded but not under load shouts electrical to me. Failing kill switch, bad stator, bad key switch, ignition issue… All things that can go bad on “premium Italian electronics”.
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agreed but I’ve had the same issue twice this year where I had the thing right on the limit of being too rich and it actually started to 4 cycle in the higher rev range but was OK where it initially came off of the corners. Both were weird pocket cases of me messing up the carb tuning but it could happen.
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