Hrmm..
The only problems I have with my Vmax7 is that it really really doesnt like it idle.. I generally have to set the heli down with a little 'extra' stick, just before hovering.. or it dies as soon as I stand back up. But it's always done that..

What percentage nitro are you using, etc?

I havent noticed my carb/venturi being loose, but then I've never taken off the screen that's on it.. guess I could check it for ya...

About the only the I can suggest, and I realize this is a DUH answer, but play with your needle valve a bit, and see if your running just a click or two too rich perhaps?

Also, change the glowplug.. seems to me like the vmax-7 plugs dont last very long.. I've had my 7 for about 4 months, and gone through 2 plugs allready.