look on here for the "clear tube method" where you align your floats to get the most gas in the bowl you can. 660 is sort of known for this. Low gas in the bowl, when you tilt back, jets come out of the gas if it sloshes around. (don't miss those carbs)
I had an almost really bad wreck because of this happening. I let off 3/4 of the way up a huge hill, got back on it...nothing. SLid all the way back down and rolled. Very Lucky guy!