I've been having this backfiring and bogging issue, It only happens under heavy throtle, like from a stand still if i go full throttle it will accelerate to about mid speed and then backfire and bog, if i ease into the throttle everythings fine, I've tried leaning and richening the HSN but to no avail, the engine is a .21 vertex with about a gallon through it, kinda stumped any help would be great thanks guys

The lsn is to rich, when ya gun it, it floods the engine momentarily, and as it transitions to hsn, you end up with a gob of fuel in it and then a heavy optimum air/fuel charge on top of it. When it is cool (before warmup)I would guess it does it worse, or even dies on you? Not a big deal, just lean the lsn 1/8 and see how it goes.

If re-tuning doesn't solve the problem try switching to a cooler plug or adding a head shim.

Thanks guys i'll try it out