I am experimenting with the Briggs LO206 engine at our local club track. I mounted the engine and scaled the kart to get a baseline. I am at 42.7/57.3 + 50/50 with a total weight of 345lb. On the maiden voyage, I had to narrow the whole kart (1x10mm spacer on fronts with aluminum DSM wheels and 46 1/2 inches in rear) to even get it in the ballpark. The kart turned in great, but at apex-off it was VERY free. Our club tire spec is Burris 44A, and our track is old, somewhat abrasive, and tight. I raised the seat so that the bottom of the seat is even with the bottom of the rails, I did install braces on both sides which seemed to help the handling slightly. I am running a med axle with short hubs. I tried long hubs, and it seemed to make the free-off condition worse. The question that cannot seem to be answered by Comet or Beasley is, ‘What kind of weight distribution does the 4-s like?’ The only answer I have gotten is “that sounds about right.” Intuitively, I feel that I need to move weight to the rear, but am afraid that this will only aggravate the condition I am describing. Any thoughts?
Try moving some weight forward. Bolt some lead to the steering support in the front and see if it helps your condition. With the seat in the stock position I’ve always found my 4S needs 5 lbs on the nose to handle well. Otherwise I’m running a similar setup to yours, but with a world formula. On new Burris 55s I’d have been around 54″ on the rear and narrow on the front, 5mm to 10mm of spacer.