Re: Gravity or siphon gas line
Now that's a nice mount, and there IS a big difference between a poorly engineered piece of rubber where it doesn't belong and a nice solid chunk of urethane on a welded mount, the urethane can't really move and the seatpost mount is nice and solid, as long as there's no tension or stress on that front mount it should work as well as solid to the frame... The easiest way to know it works is by riding it full wide open... if you don't feel any vibes at the grips or seat, it's working. If it feels like you got a pair of vibrators in your hands going down the street, well... it's not working.
Personally on mine I cut a slot on each side of my frame's down tube and slid in a piece of 1" wide 1/8" thick flat stock thru the frame then welded it into the frame so the front of the engine bolts directly to the frame. The rear mount uses 2 of the aluminum mount blocks instead of that flimsy steel strap that bends as you tighten the bolts down so it's a rock solid fit on both sides, the engine will Not move no matter how hard you try to push it side to side. As for vibration... There's none at the bars or seat at 9500+ rpm.