I would say 10 - 15% Nitro is better.

Is this a Surpass II? (If it is, it will have a hose running from the intake manifold to just in front of the cylinder - and if it has a nipple in those two places with no hose, that could be the problem right there)

I would also check valve clearence - When there is no pressure on the valves, they should have the slightest amount of play in them - Almost undetectably slight.

But one of the things that raises a red falg with me is that you say it won't change if you open the needle valve. You might have an obstruction in the valve housing. Try removing it and giving it a thorough cleaning.