Very rough running/cuts out when hot

1800 32-34 DMTL Weber-carbed auto cabbie was running fine before I dry-stored it for four years.

In May I changed the oil and re-started it, and now once fully warmed (six or so miles) it starts coughing if taken above about 2,000 revs, unless very gently, and also cuts out at lower revs sometimes. Giving it more throttle just speeds the cut out, and it can sometimes stay running at idle/low throttle, though not always. Once it starts cutting out it will do so every 800 yards or so. It will eventually re-start after cutting out, bit it takes a lot of turning of the starter and will will often start on just one or two cylinders before cutting out and/or backfiring. Eventually it will start on two or three and a bit of throttle and it will rev up, fire on all four and we can get going again, for a bit.

Before it went into store I drove it 30 miles at a time with no issues.

To date I have:

Checked the fuel tank - no dirt.
Changed the fuel filter.
Re-built the carb using a Weber kit. This may have helped slightly, but I'm not sure. The inlet filter on the carb fuel banjo was clear.
Changed the condenser and points.
Swapped the coil for another coil (not a new one).

It starts and runs fine for the first five to six miles. A decent increase in throttle causes it to cough, but backing off will leave it running OK. Going uphill it therefore a problem.

This has been going on all summer, but I've had little time to deal with it. The fuel is fresh.

Any thoughts? I'm going mad 

What's the rubber flange that the carb sits on like? Any splits, does the car cut out if you wobble the carb or idle change if you spray carb cleaner/easy start etc near it?
Have you checked the mixture, co2?
How old is the ignition side of things, HT leads, dissy cap, rotor arm?

mark1gls said

What's the rubber flange that the carb sits on like? Any splits, does the car cut out if you wobble the carb or idle change if you spray carb cleaner/easy start etc near it?
Have you checked the mixture, co2?
How old is the ignition side of things, HT leads, dissy cap, rotor arm?

Flange seemed OK when we had the carb off. Good check  again though.

It passed the MoT on the old carb set-up.

I had wondered about HT leads and cap.

 

may be carb icing issues
http://www.clubgti.com/showthread.php?144497

also if you have lost the restrictor for the fuel return the webers dont like it. try removign the swirl pot and put the pump feed direct to the carb, block the return. if car runs great after pop an 8mm weldign tip in the fuel return and put the swirl pot back on (make sure its all nice and clean first!)

Update:

Bypassed the swirl pot - same issues.

Blanked off the cold air port on the air intake - only hot air now reaches the carb - same issues.

Pulled off fuel pipe at carb as soon as it died. Fuel in the pipe, and fuel dropped out of the inlet. Turned the engine over with the pipe detached and fuel gushed out, so we now we have pressure in the fuel line when the engine is running.

Most confusing ..