backfire??
 

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

RE: backfire??
 

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.

RE: backfire??
 

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

RE: backfire??
 

Thanks guys i'll try it out :D