engine stumble at 3100 rpm's

[chris and heidi]

May be you can help me with this? When I'm accelerating, and the engine hits aboutat 3100 rpm's it seems to flutter or cut out, similar to what a rev limiter would react like but not so consistent. the motor did this before and after rebuild. with the exception of said problem the motor runs great.
the motor is a stock type 4, 2.0L, F.I., 1978 VW transp. while rebuilding the long
block, to stock specs, I replaced, with new, the : plugs(bosch super), wires (bosch), coil("flame thrower"), points>(pertronix ignitor), cap, rotor, fuel injecters, cold start injecter, cyl head temp sensor. I am using the stock vacuum/ centrifugal advance distributer, set @ 7.5 deg. BTDC. @ 950 RPM's. I did not check the ignition timing at any other rpm, although in doing the timing for the 950rpm, I noticed when i brought up rpms the timing was advancing. how can i check if both the vacuum + centrifugal advance are both working properly? does this sound like a distributer problem, or something more like air flow /computer stuff.
thank you to all
sincerley, chris

[Dave_Darling]

Have you checked the fuel pressure? Does this happen only under load, or can you make it occur with the car out of gear? Fuel filter? Kinked fuel lines?

Those are the first ideas off the top of my head.

--DD

[JeffH]

As well as the filter, junk can lodge at the entry neck of the filter so the filter still looks clean. also on a bus the outlet line at the fuel tank is vulnerable to clogging.
I had this sort of problem even after pulling the tank and finding the interior looked pristine.
I ended up bridging the inlet and outlet lines with two T fittings and a hose between and it has'nt stumbled since.