Stalling after high RPM's

[veedublover12]

I own a 69 Bus but my brother owns a 71 Super Beetle with a 1600 Dual Port Single Carb stock engine with a Bosch 009 with Electro-Magnetic ignition. Engine was recently (less then 9 months ago) rebuilt by reputable VW mechanic in our area. The Bug runs great except when run to high RPM's (such as freeway speed in 4th gear) and then when put in Neutral to downshift or slow down the engine stalls. I have never experienced this problem in my Bus, only when the engine is cold, but this is after the engine has had significant time to warm up. I thought maybe a manifold leak or carb tuning issue. Does anyone have any suggestions?

[spiffy]

Sounds like a rich mixture problem to me.

[hambone]

Check the timing too. Make sure the auto choke and cutoff solenoid are working.

[Amskeptic]

The most common cause of stalling-while-braking, is insufficient airflow through the carburetor. You need to distinguish this symptom from others in the following manner: if it stalls-while-braking only when cold, go directly to the lower option here. If it stalls-while-braking when warm, cold, moderate, and any other time, then work here. If you have an air bypass carburetor (big brass air flow screw on the side), crank the big brass screw out and raise your idle speed by 100 rpm (even it is too fast). Adjust the mixture screw underneath IN until the rpms just drop. Bring it back out for best idle and go another 1/4 turn past that. If your idle is still too fast, try retarding the timing a couple of degrees. Your bearings will love you for it, your highway temps will drop a tad, and your power output will too. We are trying to get as much airflow through the carb as you can stand, so we are skirting at the edge of too fast an idle at too retarded a timing. Last resort is to turn the brass screw back in to yield an idle of 1,000 rpm.
If you have the earlier Pict 2 carb ('69 bus), you are thwarted by the fact that all you get is an idle speed screw that also dictates fast idle cam choke rpm, and a mixture screw with a spring to hold it in place. You can still do the timing retard bump the idle speed up trick, but results are trickier. The electromagnetic cutoff is a critical component for idle mixture behavior on the Pict 2. If you unscrew it just a bit with an idling engine, and the idle improves dramatically, things are lean in the idle passages/float level.

Stalling while mostly cold, check choke adjustment, make sure choke plate moves easily, make sure fast idle cam is actively contributing to fast idle. Spec calls for .020" clearance between fast idle cam lowest step and screw on end of throttle lever with choke off with the Pict3 ('71 beetle), it is dependent on the idle speed adjustment on the Pict 2 ('69 bus)
Heat riser warming up? Cool humid mornings in Portland? Air preheater hooked up? Thermostat working? Cable from flaps to preheater valve functional and adjusted (1969), thermostatic preheater working on the Superbeetle?

The 009 distributor is an oxcart among Ferraris. Get thee the correct vaccum units.
Colin