Ok i'll try and help. Firstly if you are still running a dumpvalve then take it off because the system will run better without it.

Poor revs and stalling could be:

1. Leaking oil filler cap and dipstick. Breather going to metering head at bottom.

2. Crankshaft oil seal (in bell housing)

3. Auxillary air valve, the little gizmo under the inlet manifold clamp the pipe going to the throttle body and if the revs drop the valve is stuck open and shouldn't. (do this when warm).

4. Any air leaks before combustion

5.Or too lean or rich a mixture


Hop this helps you.

Jonathan