TheSamba.com :: View topic - 34-Pict 3 Adjustment

Sun Jun 19, 2016 3:16 pm

First the facts: 1966 Beetle; rebuilt 1641 engine with fewer than 100 miles; new (with the rebuild) Bocar 34-Pict 3 carburetor.

Now the problem: When the engine was installed, the idle was set for around 900 RPMs and worked fine — for a while. But then the car would stall when stopped. I’ve tried adjusting the carb with no success. With the volume control screw set at 2 ½ turns open, I’ve adjusted the air bypass screw from closed to 5 turns open, and there is no perceptible change to my “does not idle” problem. What do you think? Gunk in the bypass chamber? Timing? Throttle plate leak? Ghosts?

I’ve searched the forum and there seem to be 100 ways to go to diagnose this problem.

Thanks, Terry

Sun Jun 19, 2016 3:20 pm

Here is the right way to adjust it: http://www.volkzbitz.com/34pict-3---4-and-h30-31-adjustments.html

That must be done after timing the engine. What distributor do you have? Also have you set your valves?

Sun Jun 19, 2016 8:46 pm

Could be a number of things. I've had this issue before and it turned out to be the idle shut off valve. It is screwed in on the left side of the carburetor and sometimes the wire connector is loose or has popped off or the valve itself could be broken.
http://www.jbugs.com/product/049129412C.html?Category_Code=vw-dual-port-carburetors

Wed Jun 22, 2016 1:53 pm

Thanks Brian and Zylinderkopf.
I'll do a valve adjustment check, check the timing (I have a Pertronix Flame Thrower) and check for loose connections. The link that Brian provided is interesting in that Volkzbitz recommends 4 full turns out for the volume screw while others recommend 2 1/2 turns.
Once the garage cools down to a temperature below that of a pizza oven, I'll dig into it again. Thanks for your help.
Terry

Wed Jun 22, 2016 3:56 pm

One thing that is NEVER mentioned to use a FLAT file in the intake man that supports the Carb. Over time the flange will Warp a bit allowing for a slight unnoticeable vac leak. (may or not be a cause but does happen)

All kinds of solutions to check out....some work and others Not.

First thing I always did was to disconnect the cable, back off both Idle and mixture screws about 3 turns, loosen the three screws that hold the choke, pull back on the arm and turn the choke ccw till the choke closes and then to the right till 1/4 in open and then tighten the three screws. will adjust the idle screw on the arm to the bottom step on the cam while holding the choke wide open. Releasing the arm the choke will close to the 1/4 preset point.

Engine is ready to start so I drip in a couple drops of gas or use the arm to activate the Carb pump spraying a couple of times. Pull the arm back allowing the Cam to drop down with the screw on a higher step on the Cam.

Turning the key should start the engine w/o touching the gas pedal (have done that 100's of times being by myself in the shop)

Engine is now running at a fast idle with the choke being partially closed. It will open on it's own or you can wait 2-3 mins, pull on the arm and the Cam will return with the choke being wide open.

Now I would screw in the large screw until the idle is where I want it. Then the small screw until the engine falters and then back of 1-1/2 turns. Then I would redo the large idle screw again and then repeat with the small screw. Will do this 2-3 times until I am happy with the Idle after a 2-3 times of blipping.

This done will reconnect the cable at the barrel.....replace air cleaner and road test.

Just one old mechanics way of doing a 34-3.

Thu Jun 23, 2016 3:14 pm

Ask six people how to adjust the idle and you'll get seven answers. The scary part is how some of them just don't work well.

Please warm up your engine with a drive before even thinking about touching the mixture screws. The manifold needs to be at operating temperature, and the oil needs to be thin enough so pump drag isn't affecting your idle like a lethargic air conditioning compressor.

Like Brian said, check your valves and set your timing first. If there is even a smidgen of doubt in your mind as to ANY of the settings or adjustments, feel free to ask. And be prepared for seven different answers. :P

Robbie