Stumble Coming to a Stop

[Thehate916]

I've been chasing an issue and am at my wits end so I figured I'd make a post and see if the experts here on TheSamba have any ideas!

1600sp, Chinese 34 pict3 carb, SVDA distributor. The car runs great other than an occasional stumble I cannot seem to figure out. When coasting in gear coming to a stop, the car will sometimes feel like it wants to die. The idle drops and the engine bogs, which I resolve by blipping the throttle. Today I took it out for a test drive after messing with the carb settings for the 10000x time, and decided to see if the car would completely die if I let it. The car never shuts off, but the idle feels rough and slow until I blip the throttle, which solves the issue and the car runs per usual. The issue makes me hesitant to drive it in traffic because I worry about being stuck at a light with fast moving, much larger cars zipping by. The issue is intermittent but occurs enough to be a problem.

Initially I figured it must be how I have the carb setup. I've been through a couple different methodologies of adjusting the carb with no difference. I know it's not the distributor because I was previously running an 009 with the same issue (among others). After the change to the SVDA, the off idle stumble is gone but the "wanting to die coming to a stop" still happens. Then I thought it might be the clutch dragging the engine down, but triple checked all adjustments with no change. Today I removed the idle jet and cleaned it with brake cleaner/my air compressor with no difference.

Any ideas are greatly appreciated!!
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'68 Beetle project

[OldSchoolVW's]

[Thehate916]

[KTPhil]

I have found that even on a well-done rebuilt carb, the stock carb's choke unloader is sometimes fooled by sudden throttle closings.

Before the engine is fully warmed up, but warm enough to not need full choke, it runs really well (no stumbling or lag). But sometimes, on quick throttle closing, I think the vacuum present unloads the choke a little too much, and it will idle low enough to sometimes die. This happens most often after about one minute of driving.

I adjust the choke slightly more closed, but not enough that it isn't fully open after about 5 minutes.

This seems to eliminate most (though not all) of the issue.
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[busdaddy]

Let's discuss how warm the bottom of the manifold and the heat riser tubes get, and also just exactly how you are setting your idle mixture.
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[Thehate916]

[busdaddy]

The heat risers should get too hot to touch after a couple minutes of running.

The smaller mixture screw should be played with when fully warmed up in and out to reach peak RPM, then turn it in slowly until the RPM drops by 50. If you have it set too rich sudden throttle closing can cause a buildup of fuel, even worse if the manifold is cold, and even worse if that China carb lacks a dashpot to dampen the closing of the throttle.

Most of that "Smog crap" everyone removes from thier cars to "improve performance" actually plays a big part in making it run nice and drive smoothly, cheap or missing parts come with a price.
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[Mikedrevguy]

Has this same/similar issue in my son’s 1974 ,1600, 34 pict, 009.
Discovered the idle solenoid was loose.
Tightened it up- issue went away.
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76 914 with 2260
69 Bwajaja
"The wise speak because they have something to say; while the foolish speak because they have to say something." Plato

Illigitimi non-Carborundum!!

[wcfvw69]

My old dual port bay bus had a brand new EMPI 34-3 carb on it when I bought it matched to an aftermarket mechanical advance only 009. Yes, it ran terrible. It also had a craptastic aftermarket fuel pump putting out 5 PSI. I installed one of my rebuilt German Pierburg fuel pumps.

I restored a correct 211905205Q DVDA distributor for it. It ran a bit better but the carb was just not working right. Curious, I disassembled the Chinese carb. I pretty shocked at how bad the tolerances and slop were in the linkages and other parts. I cleaned it spotless and blew out all the passages. I reinstalled it. Shockingly, it still idled like crap and accelerated poorly.

I had a worn out German Solex 34-3 carb. I sent it to Tim to have him install new throttle shaft bushings. I then rebuilt the rest of it when I got it back from Tim who did a great job.

I installed the rebuilt German Solex 34-3 carb. The engine fired right off. I dialed in the mixture and idle adjustments and the engine just purred. Took it for a test drive and it was liking driving a new bus.

Amazing what happens when we reinstall the original, rebuilt/restored VW German parts that were matched to each other by those smart German Engineers.
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[PiperFixer]

Adding my two cents.

I had this issue as well. Just replaced my Chinese carb with a Volkzbitz. Haven't driven much but it seems like the stumble has gone.
I have a Sparxwerks SVDA and square top Pierburg, German 34 Pict 3 and it runs and idles really well now.

I still get some popping when it's cold but I have a new muffler ready to install. My old muffler is a conglomeration of rust held together by dirt and undercoating.
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Orange 72 Super
A&P IA

[jinx758]

Car runs great ... but stumbled at lights &/or stops.
That's an oxymoron.

Your setting is too rich.
Dwell actually plays a role in this too.
Fast idle cam screw also.
Drops of oil in recess on distributor shaft felt ?
Does the advance snap back quickly & all the way when you twist rotor ?

Every "new Chinesium" carb should be thoroughly cleaned & set float level before install.

Trying to help ... stay safe

jinx
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It's not unlike the same difference ...

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38mm EGAS Carburetor

[heimlich]

I wouldn't go throwing parts at this problem until you figure out where the issue is. You'll just waste money throwing it at parts.

On Autosticks you have to set the idle RPM a little higher than usual to solve this issue. Sometimes hoses can get connected backwards and cause this issue.

On the China carburetor subject I had a customer with a shop tell me yesterday that CIP1 has made some progress in this area. They have a China 34 PICT 3 carb that works well. I was surprised but he was adamant about it.
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[Thehate916]

Thank you guys for all the help I knew this would be the spot to come!

As for what I'll try before I throw parts at it, I will pull the carb and give it a good cleaning/float level setting. Following that I will double check the dwell. I'll give an update as soon as that stuff is done!

EDIT: Took more time to adjust the carb today. I gave the engine time to settle instead of trying to do everything in 1/2 turn increments. The problem seems to be better, although I think the idle is set a bit high but I will adjust next time I have some time to burn in the garage.
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'68 Beetle project

[BMFBMF]

Post photos of your engine? Where are your vacuum hoses connected to the carb?
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-----Slava Ukraini-----
1971 Stock South African Beetle 1300 : My mom's european "Thin Chick" spec. Completely stock with torsion bar front, swingaxle rear, smooth hubs, single MC, 40 mm shoes, 31PICT3 carb and 5 bolt drums all round, currently Running a 1976 SF:AS engine with the original SF:AD engine overhauled in a box, waiting to go back in one day.

[VW_Jimbo]

It sounds like the base setting for the throttle plate is incorrect. Start there.
1.) Choke open, all the way
2.) Disconnect the throttle cable
3.) screw throttle plate stop out
4.) screw it back in till it just comes into contact with the choke cam
5.) screw it in 1/2 turn more
6.) reset timing, idle speed and idle mixture
7.) go for a test drive
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[passionre]

Starting with a known proper valve adjustment, dwell adjustment (if points equipped), and timing set at 31btdc @3000rpm (vac advance disconnected)...adjust your carb as per the instructions given here>>>
>>> http://www.vw-resource.com/.
You're describing a rich idle mixture issue...but these little AC VW carbs are funky compared to the rest of the 1970's world.

If it's any consolation, my Chinese Amazon knock off carb actually works pretty well, even with the originally installed jetting.

[vamram]

The eBay Special Chinesium 34/3 carb on my '73 works great. Dialed in at just shy of 3 turns out of the volume screw, and just over 2 of the large screw. Throttle cam screw properly set. No stumble, no dropping to low idle when stopping. Follow Busdaddy and Jimbo's advice for adjustment.
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[ashman40]

[Thehate916]

Update: pulled the plug out of #1 and they’re black, the car has been running way too rich. I’ll get some new plugs and update after messing with the carb yet again
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'68 Beetle project

[KTPhil]

BOLD are my additions: