Hi all, I need some help.

I am putting a new MVVS 91 on my Vector Flight Extra.

I broke the engine in on a stand, it ran flawlessly. I have it on the plane now and it runs well, but from time to time when I advange the throttle to full, the engine will quit suddenly just after it hits max rpm. It doesn't sag and die like it was leaning out, it just quits immediatley. I assume this has to do with my tank plumbing, but I've been through it several times to no avail. I am running a three line system in a Dubro tank. I have used a piece of fuel line, notched at the top, to extend the vent inside the tank to so that it reaches the top. Using the old Mark I Suction Device (mouth), I can detect no leakage in the tank/stopper/lines. I am running a BCM Pitts muffler. I have tried blocking one of the outlets to get a little extra muffler pressure and it still quits. The tank is completley encased in latex foam so vibration is not the issue either. Any ideas? I was hoping to fly this bird tomorrow, but I'm not going to if I can't get things sorted out.

Thanks!