Mine is the regular Webra Speed 1.20, not the pumped, but from experience with it, I concur with the previous post. be patient with your adjustments to the needles, and use SMALL adjustments especially on the low speed needle. One thing I should point out is that even after about 8 years on mine, it has NEVER had a perfectly smooth transition. That is not to say that it dies all the time like you describe, because mine certainly does not. It runs great, has awsome full power and great idle, it is just that I could never get a perfect transition from idle to full power. It just sputters a little going through mid-range, and is worse about it if I advance the throttle more slowly, than if I advance power more smartly. In all these years of flying it, I can actually only remember it quitting in flight once, so it isn't a big deal, it just sounds funny as it transitions. It kind of "clears it's throat" and then comes on up. Just FYI, I am using a regular K&B 1L plug, low nitro (5%) fuel, and also a pitts style muffler, though mine is an older "J-Tech" unit.

Good luck, Lee