This is really annoying the hell out of me.
This is a run down. 34/3 German carb, New single vac distributor.
Idols great, couldn't be better. Points set and reset, checked and replaced, .4mm gaped. Dwell reads 50. Valves set to .6mm . Checked for carb and manifold leaks. Checked fuel pump and throttle tube and tried all setting between + and - on the pump. Carb cleaned out and rebuilt three times. Tried 130 and 135 main jets. Carb set as per manual guidelines. Air cleaner checked for obstructions. New condenser,plugs,leads rotor and cap.Then rechecked with old ones. Coil checks out ok. Choke checked and works fine. Timed to 30 BTDC at 3000 rpm. Timing falls to about 10 BTDC at idol. Fuel lines checked.

It runs great(no flat spot) for the first couple of minutes when the choke is closed but then it has a really bad flat spot as soon as you push the accelerator after the choke opens. Have to rev the balls out of it to take off. Same problem happens when under no load. If you leave the accelerator in that position the motor will stall. The flat spot can be adjusted out a little bit buy screwing the bypass screw all the way out but it revs high between gear changes and fouls the plugs and blows black smoke. Way to rich.

Don't know what to do next except buy a new carb. Is there somthing I am missing? I am all out of ideas. This is really frustrating!

Only thing that ops up is the valve adjustment of .6mm...which I am assuming is a typo and actually .006" (six thou).

Running well ON the choke, indicates that the engine is lean, when it flat spots OFF the choke.

Provided you have not mixed up the main jet and air corrector,
I would be more inclined to look at the idle jet and passage...(idle cut-off solenoid not restricting oening?)
and also the accellerator pump nozzle and pump stroke.

Most carbs run on the idle jet for some time before the main even operates.
And the accell pump can fill in lean spots at the crack of the throttle.

Before checking all that, it may be worth checking the float level.
This controls a lot of other functions with in the carb, like emulsion tube action.

Yep typo .006 on the valves. Cheers mate that gives me somthing more to think about. I have checked the idol solinoid and clickety click. I am off to tinker again. I was thinking last night maybe a problem with the pilot jet? Might try backing it out a little and holding it there. But I will check the carb float again and the idol circuit.

sounds like a leak to me

How white are your plugs ??

Try spraying fluid around carb, manifold boots and gaskets

I had flat spot problem and i just put a bigger main jet in the carby and fixed it all, Some say the vw bug was set up a bit lean from the factory.

and some say you are compensating the air leak with extra fuel

Hi

There are 2 basic 34Pict 3s. One is single vac advance, other is dual.

The dual can be picked by vac port pointing out the back of the car.

From memory and it was 20 odd years ago, the early dual vac carb had a huge main and air jet, the air was something like a 140Z, the main about 140, don't quote me on these sizes, I may be out a little.

It was a economy mod to fit the early carb with the late single vac jetting, this was a 60Z air and a 125 main, again my memory is getting faded.

So check these jet sizes along with other suggestions above, also your manifold preheat after everything else has warmed up should sizzle both sides if you lick your finger and touch it.

Steve

I was pretty sure it wasn't a leak. It idols really strong and smooth. But checked it again anyway. Rechecked the carb AGAIN. Its a single vac German Solex. Seemed to all be in order. Checked the coil again nice blue spark and the two resistance measurements where within specs.

The coil is kinda old so I thought I would go get a new one anyway. I mean its only $50 more and it couldn't hurt. After all that it couldn't just be the coil, right?

Problem gone, damn coil! Runs great now.

Thanks all.

Wow, good to know it is solved!