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stevedubya
Samba Member
Joined: May 05, 2022
Posts: 20
Location: CA
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 Posted: Wed Jul 02, 2025 5:46 pm Post subject: Help!!! I can't get my carb tuned |
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Hi All - I have a 1600dp with a 34 pict-3. Been trying to tune the carb using all the good advice out there and have hit a wall.
*I can't get it to idle once the engine is warm
*It runs incredibly rich, or at least it used to.
Note: I have an Alternator and the correct fuel pump with the shorter (100mm) pushrod. Before I added gaskets, it was running crazy rich. I added gaskets so that the fuel pressure is down to 3 psi. I'm not yet sure if that solved the running rich problem yet.
But I still can't get it to idle with the choke open.
I followed Ron and Dave's procedure -
*valves set
*timing set (SDVA, so 7.5 BTDC)
*turn the Volume Control screw out 2.5x
*turn the Bypass screw 2/5x
I start it up with the choke closed. Once it's warm and the choke opens, it dies. Also, I noticed something strange - when I turn the Volume Control screw all the way back in to the stop, the engine not only continues to run, RPM actually increase a bit. In other words, the Volume control seems to have no impact.
Shouldn't the engine shut off with the Volume Control screw all the way in?
Question: What am I doing wrong and/or what else could be causing this? |
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VW_Jimbo 
Samba Member
Joined: May 22, 2016
Posts: 11162
Location: Huntington Beach, CA
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| Posted: Wed Jul 02, 2025 7:07 pm Post subject: Re: Help!!! I can't get my carb tuned |
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It sounds like you have false air entering the intake manifold. Time to run a smoke test and find out what is allowing air into the manifold, without the carburetor’s permission.
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modok
Samba Member
Joined: October 30, 2009
Posts: 27667
Location: Colorado Springs
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| Posted: Wed Jul 02, 2025 7:29 pm Post subject: Re: Help!!! I can't get my carb tuned |
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So it's "rich"
BUT
stalls when choke opens.
Do you realize that makes no sense? |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16573
Location: North Florida, USA
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| Posted: Thu Jul 03, 2025 8:49 am Post subject: Re: Help!!! I can't get my carb tuned |
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How have you adjusted the throttle arm screw that rests on the fast idle cam?
It is very common to mistakenly think this screw is adjusted to control the fast idle speed/rpm. This screw on the 34Pict carb is to adjust the warmed up throttle position which needs to be fully closed but not resting on the walls of the carb throat. Basically, loosen the screw so it doesn't touch the lowest level on the fast idle cam; screw it in until it just touches the cam; then screw it in another 1/4-turn to keep it off the throat walls but still closed. When the choke is fully warmed up and the throttle fully closes... ALL air-fuel should be flowing thru the bypass circuit around the closed throttle plate. See below pic.
The volume and bypass screws control flow thru the bypass circuit. If you adjust the throtte plate open any amount so air flows past it at idle when warmed up your bypass circuit becomes less effective. This sounds like what you have?
| VW_Jimbo wrote: |
| It sounds like you have false air entering the intake manifold. |
I agree. Here is a quick test...
Once your engine is sufficiently warmed up and no longer running on the steps of the fast idle cam (or maybe on the last step of the cam to keep the engine idling), remove the air cleaner and cover 50% the opening of the carb with your flat hand to restrict the air flow down the carb. Slowly slide your hand to cover more and more of the opening. You are "choking" off the air flow down the carb. At some point you will start to choke off the air needed to keep the engine idling at the same rpms. This is the same effect as closing off the throttle... the engine rpms should audibly go down.
If on the other hand, the engine rpms improve or smooth out... this means you likely have an air leak which is leaning out your air-fuel mixture. By choking off the air going into the engine you are enriching the already lean air-fuel mixture (bringing it closer to the ideal air-fuel ratio) and the engine runs better. If this is what happens... you need to go on the hunt for an air leak (aka. vacuum leak).
My favorite method for this is to take a can of spray carb cleaner with its thin red straw connected to the nozzle and (at idle) spray leak points between the carb openeing and the intake port on the heads. Anywhere that air could leak into the intake flow. This means every hose and vacuum cap; every screw, gasket or o-ring... any place air could seep past and lean out the air-fuel mixture. A common place on old Solex carbs is the throttle shaft bore on each side of the carb. These wear over time and air leaks along the shaft into the intake. It is hard to reach as the throttle shaft flanges get in the way. You need to focus your spray (using the red straw) in the narrow gap between the carb body and the flange of the throttle shaft. The fix for a leak here is to press new bushings into the carb body.
If spraying somewhere causes a change in the engine rpms... you have found a leak!
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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heimlich
VWNOS.com
Joined: November 20, 2016
Posts: 7502
Location: Houston, Texas
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| Posted: Thu Jul 03, 2025 1:00 pm Post subject: Re: Help!!! I can't get my carb tuned |
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What size idle jet do you have? How much ethanol is in your gas where you live?
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