I have the same issue with mine on a stock TM34SS carb (220 main, 30 pilot, 2nd clip on needle 1.5 turns on air screw) but it only lasts a few seconds. I have it bored to 68mm, uni filter with lid on the airbox, boysen power reeds, FMF Fatty, running 32:1. I am at 55' elevation and the temp today was ~80 degrees. During my break in riding I had the stock 240 main and 3rd clip on the needle at about 70-75 degrees and didn't have the issue but it ran rich. I think I am going to get a leaner needle and try one size smaller on the pilot.

If you or someone else figures it out let us know. I will take any advice to help me figure out the jet settings.

PS: I see you guys talk about squish...can someone enlighten me on what this is please...thanks..