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Sat Jun 10, 2017 6:51 pm

I put a carb on my 1972 bug after the old one was taken off and found to be not rebuildable. It seemed to run better, but extremely rich, I followed the directions provided with the carb and tuned it, it ran fine and sounded great, i did this while warm like it said. I started it today, and it wouldn't idle. So I turned it back to the factory specs and tried again (with it warm) and I just can't get it to run right, it'll idle for 10 minutes and die, it will pop like hell (lean) when I rev it, but if I richen it it will have black smoke coming out of it. The idle speed does not remain the same, itll vary from fast to almost dying to dying. And the bypass screw (small one) and idle screw (big one) have almost no bearing on how the carb runs until they are adjusted well over 5 turns from stock placement (The directions say it should only be about a half a turn).

It has "performance headers" on it with an empi stinger exhaust, and it has the stock jets in it, although it came with bigger jets that I can put in. Would "performance headers" require me to put in the bigger jets?

It is an empi carb. I am just fed up with throwing parts at it, and each time it hits me with three more problems! I have owned the bug for a month, worked on it nearly every night, and it still isnt on the road!

Sat Jun 10, 2017 11:12 pm

Speedbird73 wrote: …the bypass screw (small one) and idle screw (big one) have almost no bearing on how the carb runs until they are adjusted well over 5 turns from stock placement (The directions say it should only be about a half a turn).

It has "performance headers" on it with an empi stinger exhaust…

Right there, I think you might have answered your own questions. You only get to use the stock settings if every part on the car is stock. Make sense?

Have you gotten it to run on a long highway drive yet? If you do that, then pull over and let it cool off, can you pull the plugs and get us a picture? That will help narrow down the mixture discrepancies, if there are any.

BUT if the carb screws have no effect on the idle speed and mixture, you need to find out where your car is getting its air and fuel. Could you post a picture of your engine for us, so we can start recommending places for you to look? A large vacuum leak coupled with high fuel pressure or high fuel level settings can mask the adjusting screws, but a vacuum leak can also screw with your adjustments and drivability.

So to recap:
Other engine modifications?
Plug reading?
Engine pic?

Help us help you by answering those, and we'll go from there to get your bug running right.
Robbie

Sun Jun 11, 2017 3:21 pm

It helped me to understand the function of the carb when struggling with idle issues.

The principle for the 34 PICT-3 is that the throttle flap closes entirely when you let the pedal go. The fuel/air mix bypasses the flap and is sucked into the intake manifold from under it:

In other words, the fuel passes through the Pilot Jet (#6) and is controlled by the Volume Control Screw. The amount of air is controlled by the Air Bypass Crew.

You mention that it ".. pop like hell when I rev it...". That indicates that it is not just your idle that is not working well! Once the thottle flap is opened (rev'ing the engine), the idle function has very little influence on the fuel/air mixture, if any.

Mon Jun 12, 2017 5:49 pm

34-3 start at 3:14 but watch the whole thing. There's another video from the same channel which provides more info into the previous models.

Mon Jun 12, 2017 7:13 pm

Did you clean the carb before installing it? I know it sounds stupid, but all new carbs must be thoroughly cleaned before you install them. There's tons of junk from manufacturing that never gets cleaned out before final assembly. You may have a blocked circuit that is causing your idle problem.

Good Luck.

Tue Jun 13, 2017 5:23 am

Speedbird73 wrote: .... the bypass screw (small one) and idle screw (big one) have almost no bearing on how the carb runs until they are adjusted well over 5 turns from stock placement (The directions say it should only be about a half a turn).
Boble wrote: In other words, the fuel passes through the Pilot Jet (#6) and is controlled by the Volume Control Screw. The amount of air is controlled by the Air Bypass Crew.
As Boble pointed out it seems your understanding of what the screws are used for is incorrect. The small adjustment screw (volume) is for controlling the ratio of fuel to air at idle. The large screw (bypass) controls the amount of air (and indirectly the amount of fuel) that "bypasses" the throttle plate. This replaces the need to open the throttle to raise the idle. This larger screw is used for adjusting the idle rpms once the volume screw has been adjusted.

Also, make sure the screw at the end of the throttle arm is adjusted correctly as this will have a big impact on idle. This screw should be adjusted such that when the carb is warmed up (choke is OFF and the screw is resting on the lowest level of the fast idle cam) the screw is turned in 1/4~1/2 turn from just touching the cam. This means when the throttle plate slams shut the pressure is on the cam and NOT the throttle bore. This keeps the throttle plate from wearing a groove into the inside of the carb throat.
Don't go nuts here... you do NOT want the throttle plate opened too much. From the pic above, you can see there are a series of holes just above the throttle plate where fuel (red) flows out from. This is the progression circuit. This starts flowing as soon as the throttle is opened. You do NOT want it flowing fuel at idle as this will defeat any adjustments from the two adjustment screws.

I'd agree with the above comment about cleaning your carb. If you threw your carb in straight "out of the box" it likely has dust in some of the internal passages. The carb needs to be disassembled, soaked over-night, washed and all passages blown clear with an air hose.

Tue Jun 13, 2017 6:22 am

Up until recently I had a relatively new Empi carb on my car as well, and experienced what sounds like a similar issue with running rich, plus inconsistent idle and run-on/diseling after shutoff. This was an Empi 34 pict 3 clone (installed by PO), on a 1971 standard Beetle w/ basically stock 1600 DP engine.

I played with it quite a bit (using proper tuning, timing, choke adjust, etc. procedures, per Bentley manual, et al.), and was able to get somewhat acceptable performance out of it, but not really ideal. The idle would always "wander" over time -- inconsistent, plus definitely ran / idled on the too rich side, despite having proper jet sizes (or Empi jets w/ proper numbers stamped on them, anyway -- who knows if actually correct diameter/spec.?).

The diseling / run-on after shutoff problem I wasn't able to resolve either, despite swapping two different (and verified working) shutoff solenoid valves on it. Final conclusion was to throw out that Empi repro carb, and get a rebuilt stock Solex 24 pict 3 from Volkzbitz.

And man, what a difference! Car runs great now -- good idle, properly lean, and no run-on after shutdown. I am impressed, and glad I made the switch. :-) Just my $0.02 worth...