KA SR/JR on same motor

Has anyone used the same KA to run both SR and JR races? In addition to changing the header, is it just High/Low needle adjustments on the carb?

Are some motors better JR vs SR?

My son is 13, won’t turn 14 until next May. He’s currently 135lbs and already 5 lbs over in KAjr. I assume by next spring he’s going to be 145-150.

We have 2 tracks close to home. One might allow him to run KA Senior, the other might not.

I would assume but don’t know for sure that the carb settings are the same for jr or sr. The manual doesn’t suggest different settings based on the header being used.

The bigger struggle is the weight. If your son actually gains weight and is up to 150 you will likely have to add close to 50 lbs of lead to the kart for sr. Why the push to move him up, is he ready to run with sr drivers?

No rush, but at what point are you too overweight to be competitive? We were already 5 lbs over at the end of the year. If he gains 15lbs, we’re 20 lbs overweight. He’s tall as well, 5’10” as a 13yo

Our senior weight is 360, so we would only need about 20/25 lbs of lead.

Pretty sure carb settings are the same. Swap the header and move him up if you can. No point in spending the year being discouraged and questioning the weight penalty all year. 20 lbs is tough to deal with.

150 means he needs probably 30 pounds on the kart. Easy peasy and about the ideal weight anyway.

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I’ve ran our motors in both Jr and Sr and it is as easy as switching the header. The needles will depend on the track, but I don’t remember having to adjust them too far from the same setting. If he’s 150 lbs, you may need to add about 15-20 lbs to the kart, depending on the kart and what else you have on it. My daughter is just little heavier than that and we run 8-10 lbs to make 360.

That’s about what I figured. Now we just sit and wait, see how much he grows between now and April.