First off...a pump WOULD alleviate inconsistencies in the fuel delivery...provided the plumbing can
supply enough fuel in the first place.

The 2.1 is a beastie of a motor...it has an appetite for fuel that is going to require a large ID fuel tubing
be used all the way from the carb inlet to the clunk in the tank. LOTS of big STs fell prey to this overlooked
element.

The motor might run just fine in normal flight attitudes, but once the nose is brought up straight and held
there for a period of time...gravity adds further to the reduction in fuel flow, and you run into problems.

Many r/c carbs do not meter linearily throughout the rpm range. If it was set slightly rich at WOT, and gets a little
leaner in the mids...it'll die.

Set your needles, Have a helper hold the model upright...like a hover. Run the throttle smoothly through the rpm
range and observe what happens. See if you can duplicate the problem safely on the ground.

Adequate fuel flow capacity first...Pump/Regulator second.

'Race