I just chased a tune all day. I put a new carb on a good running OS v-spec, old one's slide was sticking. It ran great on the starter box, started right up, idled good, good power etc. until it was put on the track. At best it would run great on the straight, i'd coast through the sweeper, then when I got back on it, it gurgled like it was loading up. Re-tuned and it would bog and try to die at half throttle, a couple times it backfired (again it was perfect on the bench). Tried numerous time, same results.

It seemed like it only acted up under load. Other suggested an air leak, it didn't seem like an air leak to me but I was willing to try anything, so I changed fuel lines, tightened carb, pipe etc.

I thought maybe a clutch problem but just pulled it apart and it seems good. Is this maybe a mechanical problem seeing it only happens with the cars wheels on the track?
Any ideas???