Sounds to me like the classic GO tuning error of too rich on the bottom and too lean on the top - normally tied in with an idle gap that is too wide (even though you checked it). It really causes problems because of the longer LSN needle in these carbs. When you change the idle gap you effectivly change the LSN setting, because the LSN sits in the spray bar, which moves in and out with the throttle slide. With the long LSN sitting so far into the spray bar on these carbs, an incorrect idle gap can cause all sorts of problems. Once you set it right these carbs are awesome.

The setting I think you have gives a false idle even though the bottom end is way rich. It will result in "sort of OK" performance, but the engine will run leaner and leaner as the tank level drops, quite often finishing a race too lean and too hot. 150C is pretty warm. 120 - 130C is more like it.
Idle gap should be around .7 - 1mm. Good way to set the gap right is to warm engine up thouroughly (run a tank). Go for a short burst and bring the buggy in. If the idle starts off high, then drops after a few seconds this is a sign that the bottom end is too rich (and possibly the idle gap too wide). Lean the bottom end 1/8 and try again. The more you lean the bottom, the longer it should idle high before dropping off. Keep leaning the bottom end until you bring the buggy in and the idle stays high (the bottom setting is not loading up the crankcase anymore with excess fuel). Once you reach this point you can now decrease the idle to a satisfactory level.
You should now have the correct idle gap and the correct (or pretty close) LSN setting. IMPORTANT - because you were running rich on the bottom before, this was probably masking a lean top end, so now reset (richen) the top end (probably around 1/4 - 1/2 turn), whatever it takes to get full revs with good smoke. As a guide, if it's a long LSN carb you don't want to be any leaner than 1/2 a turn in from flush on the HSN. Now you should be racing.
If this does not fix your problem take the tank out and pressure test it. Many a weird tuning problem can be put down to a small split in the seam of the tank or faulty O ring seal in the lid.