How to Adjust VW Idle Speed with a 34 PICT3 Carburetor

Download Article

Get your vintage Beetle engine idling correctly and stably

Co-authored by Hovig Manouchekian and Eric McClure

Last Updated: June 5, 2024 Fact Checked

Download Article

• Idle Screw Adjustment
|
• Volume and Bypass Screw Adjustment
|
• Video
|
• Q&A
|
• Tips

|Show more |Show less

When it comes to the old school air-cooled Beetles, the Solex carburetors are notorious for requiring idle adjustments. An appropriate idle speed is essential, since it must remain high enough to prevent engine stalls, but low enough to avoid wasting fuel or putting wear and tear on your engine. In this article, we’ll breakdown how to adjust the 34 PICT3 carburetor to change your idle speed.

Things You Should Know

• Warm the engine up and keep the choke butterfly valve upright before adjusting your carburetor.
• Adjust the fast idle adjuster screw so that the end of the screw is 0.004 inch (0.10 mm) away from the edge of the stepped cam.
• Use the volume and bypass screws to fine-tune the idle engine speed, and aim to get your engine to idle at 850-900 rpm.

Steps

Get Car Support Solve Any Problem

Hi there! Do you have a question about how to diagnose or fix a problem with your car? I’ve read the manual so you don’t have to. Select your make, model, and year, then ask away!

Select Make Audi BMW Cadillac Chevrolet Chrysler Dodge Fiat Ford GMC Hyundai Jeep KIA Lexus Mazda Nissan Ram Toyota Wagoneer Other *

Select Model Other *

Select Year (optional) I don't know Other

Ask

Method 1

Method 1 of 2:

Idle Screw Adjustment

Download Article

1. 1
   Set the choke butterfly valve upright. Pop the trunk and locate the choke in the middle of the carburetor. Move the butterfly valve to the upright position. This way, air will flow into the engine as it runs and you can get a more accurate reading of your engine’s idle speed as you make adjustments.

   • Ensure the air cleaner is on when adjusting the carburetor.
2. 2
   Warm the engine up by letting it run for 3-5 minutes. Turn the engine on and let it run for a few minutes. Then, shut the engine off. This will give your carburetor time to smooth out any kinks before you make adjustments.
   Advertisement
3. 3
   Adjust the fast idle adjuster screw to barely not touch the cam. Locate the throttle spring on the left side of the carburetor. Look on the top of the throttle arm (facing to the rear of the car) to find the fast idle adjuster screw. Make sure that the choke is fully open and the fast idle adjuster screw is resting on the very bottom of the stepped cam, which is the stair-shaped component behind the screw.

   • Unscrew the fast idle adjuster screw until it is clear of the stepped cam.
   • Screw it back in until it just touches the very bottom of the stepped cam—not on any of the steps themselves.
   • Now, screw it in another 1/4 turn. This sets the throttle butterfly open the required 0.004 inch (0.10 mm).
   • This screw works with the choke to give a smooth idle on a cold engine.
   • As the choke warms in concert with the warming engine, the butterfly valve in the throat of the carburetor opens and the fast idle adjuster moves down the stepped cam, reducing the engine idle speed.
Advertisement

Method 2

Method 2 of 2:

Volume and Bypass Screw Adjustment

Download Article

1. 1
   Set the volume control and the bypass screws on the left. Look just behind the throttle spring on the left to find the screws. Turn the bypass screw (the larger one) out a couple of turns. You’re going to adjust this screw several times, but you need to reach a baseline before you make additional changes.

   • The volume control screw is the smaller of the two adjusting screws. Turn it in very gently until it bottoms. Then, unscrew it exactly 2.5 turns.
   • Then, start the engine and adjust the bypass screw again until the idle runs at its highest speed.
2. 2
   Reduce the volume screw to reach the highest idle minus 25 rpm. Go back to the volume screw and adjust it (usually out/counter-clockwise) slowly until you reach the fastest idle. Monitor the tachometer on the dash to make sure you’ve reached the maximum rpm. Then, turn the screw back in very slowly until the revs drop by about 25-30 rpm.

   • A tachometer is an instrument that measures the working speed of your engine in revolutions per minute (rpm). It's typically on the dashboard next to the speedometer.
   

   Follow step-by-step to optimize performance. "I've been working on VWs for years and have a whole library of repair books. But the step-by-step instructions here for adjusting the 34 PICT carburetor are clearer than anything I've seen. I'm not usually one to follow directions to a T, but this time I did. And you know what? My Beetle is really purring now. I couldn't be happier with how it's running." - Tracy G.

   Demystify challenging carburetor adjustments. "Tuning this 34 PICT carburetor was pretty intimidating since I'd never done one before. But the diagrams matching each step really helped me picture what was going on in there. I could actually see the parts you were talking about! Following along carefully, I was able to get through the whole tuning process. And the best part? My Beetle's idling totally smoothly now. Not bad for my first go." - Chask H.

   Transfer heavy equipment expertise to light auto repairs. "After years of working on big machinery, I don't know much about small engines. But I was determined to get my VW carburetor adjusted properly. This article gave me the perfect starting point. Following the steps carefully let me put my technical skills to work, even though this was all new to me. I couldn't be more thankful to have these instructions handy." - Allen H.

   Achieve smooth and stable idle. "I've had my Beetle for ages but could never get the idle right. It was always sputtering and stalling. But going through the steps here to set the screws properly really made a difference. I took it slow and double-checked everything. Now it's idling smooth as butter at 900 rpm. What a relief to have that fixed up finally!" - Michael K.

   We want to hear from you! Advice from our readers makes our articles better. If you have a story you’d like to share, tell us here.
3. 3
   Turn the bypass screw again to reach an idle speed of 850-900 rpm. Leave the engine running and go back to your bypass screw. Continue making adjustments and checking your tachometer until you’ve got an idle speed between 850 and 900 rpm, which is the manufacturer recommendation for the 34 Pict-3 carburetors.

   • This is actually the recommended setting for most of the Solex 30-34 PICT-3 models.
   • If you can’t achieve these rpm settings, it’s possible that the threads on one of the adjuster screws is stripped. You may also have a damaged hole for the tapered screw, or a damaged needle valve or O-ring.
   • If the screws work just fine but the rpm isn’t staying stable, you probably have a vacuum leak and air is leaking the intake manifold.
Advertisement

Community Q&A

Search

Add New Question

• Question

  My 1972 VW Bug will idle when cold, but not when warm. How do I fix this?

  

  Community Answer

  I had the same issue. First, make sure you adjust carb after the engine is warmed up per the directions above. The "Volume Control" jet is usually the issue when it does not idle correctly. Make sure it is not more than 2.5-3 turns out, but less is better. If you hear any backfiring, even the slightest, the volume control jet is out too far and dumping too much fuel. Check the "O" ring on both "by-pass" and "Volume Control" jets. As you adjust out, the tightness should be consistent, otherwise the "O" ring is bad.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

  Yes No

  Not Helpful 16 Helpful 35
• Question

  I have a 1971 VW Beetle. I have had it for 10 years and am starting to have issues with it. It struggles to pick up speed, and going up a hill is a no-go. I have changed the battery and air filter. What else should I do?

  

  Ginger Benson

  Community Answer

  You may want to check your hoses and connections for a vacuum leak. You'll lose power. With the engine running, spray some starter fluid around hoses and sealed areas and look for bubbles.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

  Yes No

  Not Helpful 20 Helpful 14
• Question

  What do I do if I overhauled my carburetor and now my VW Beetle won't start?

  

  alejandro

  Community Answer

  Make sure your accelerator pump is working, if there's an adjustment adjust it so you get a good strong stream coming out. Make sure you have power to your air bypass valve, and look for leaks at the intake gasket. You might even have your float set too low, make sure it is at the top of the bowl, usually one thin copper washer under float valve. Yes, you will probably have to take it off and apart, it's easier on a bench. Check volume screw (small one) is out about 2 1/2 turns and the big screw bypass screw about 1 1/2 turns. Put it back on. It could be a lot of things, as I didn't even mention the choke or vacuum leak. But make sure she squirts first and foremost. If you still can't find the problem, take it to a mechanic.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

  Yes No

  Not Helpful 10 Helpful 11

See more answers

Ask a Question

200 characters left

Include your email address to get a message when this question is answered.

Submit

Advertisement

Video

Tips

• The Haynes VW Beetle & Karmann Ghia Repair Manual is an excellent resource if you work on old Beetles, but the book does have the diagram for the adjustment screws on the left of the carburetor backwards. The larger screw on the top is the bypass screw, and the smaller screw on bottom is the volume control screw.
  Thanks

  Helpful 0 Not Helpful 0

Submit a Tip

All tip submissions are carefully reviewed before being published

Name

Please provide your name and last initial

Submit

Thanks for submitting a tip for review!

Advertisement