More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

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vwlover77
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More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by vwlover77 » Fri Jul 21, 2017 5:15 am

L-Jetronic fuel injection I understand, but the simple 34-PICT3 carb on my ’71 Super Beetle Autostick is apparently beyond me. The problem started last summer. It ONLY happens after the engine gets good and hot from a long drive or a highway run in warm weather. When trying to accelerate from an idling stop, I have to slowly press the accelerator to get smooth acceleration. If I quickly open the throttle to pull into traffic (which is necessary with an Autostick!) the engine basically dies for around 2 seconds and then slowly recovers.

When this happened last summer, I replaced the fuel filter and disassembled and cleaned the carb. I drove the car into the Fall and a few times last winter and had no problems, but now that it’s summer again the problem is back.

I suspected the accelerator pump, so I verified that it is working. The pump adjustment was set at the mid-point. I’ve tried both the maximum setting and minimum setting and neither makes any difference.

The ignition system is in good condition, the DVDA distributor advance / retard is working properly, and I believe the engine is timed correctly.

Thoughts?
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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wcfvw69
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by wcfvw69 » Fri Jul 21, 2017 5:28 am

Tell us the Bosch number of your distributor? Is it a 113905205AH autostick distributor?
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

kreemoweet
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by kreemoweet » Fri Jul 21, 2017 9:16 pm

You actually measured the volume output of the acc. pump and found it was within spec?
Checked for lost motion in the acc. pump linkage?
Have a fully functional heat riser/intake manifold heat system?
Have your acc. pump output jet aimed so it splashes off the main jet nozzle in the venturi? (You will almost always be advised by VW myth-believers
to aim it so it misses the main jet nozzle and throttle butterfly to disappear as a solid stream into the intake. VW service literature sez to let it
splash as described).

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vwlover77
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by vwlover77 » Sat Jul 22, 2017 8:14 am

Numbers on the distributor:
JFUR4
0231167053
113 905 205 AH

So yes, it's an Autostick distributor.

I have not measured the accelerator pump volume or verified the linkage motion - yet.
The heat riser and intake manifold preheat system is fully functional, including the thermostatic flap on the air cleaner. I have installed a "restrictor" gasket on the inlet to the manifold heat tube to try to prevent carb flooding after a hot shutdown and also have installed a 1/4" phenolic spacer for the same reason.

The first easy fix I'm going to try is repositioning the aim of the acc. pump output! I definitely do NOT have it splashing off the jet nozzle.
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Amskeptic
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by Amskeptic » Sat Jul 22, 2017 9:55 am

vwlover77 wrote:
Sat Jul 22, 2017 8:14 am
Numbers on the distributor:
JFUR4
0231167053
113 905 205 AH

So yes, it's an Autostick distributor.

I have not measured the accelerator pump volume or verified the linkage motion - yet.
The heat riser and intake manifold preheat system is fully functional, including the thermostatic flap on the air cleaner. I have installed a "restrictor" gasket on the inlet to the manifold heat tube to try to prevent carb flooding after a hot shutdown and also have installed a 1/4" phenolic spacer for the same reason.

The first easy fix I'm going to try is repositioning the aim of the acc. pump output! I definitely do NOT have it splashing off the jet nozzle.

I am pretty sure, Don, that you are actually flooding it. Experiment with me.

Warm engine, set mixture to a 25 rpm drop-off lean condition (it is subtle when the tach/dwell meter is dancing all over the place, but you can hear it too)
Reduce the accelerator pump movement by one increment.
I don't have to ask you if the fuel pressure/ float level is correct and the air cleaner is clean . . . .
Anyway, see if this improves the bog a little.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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sgkent
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by sgkent » Sat Jul 22, 2017 12:03 pm

a lot of 34 pict 3 's have had their floats replaced with those hard foam ones that absorb fuel. When that happens the float sinks into the fuel and although the mechanical height is correct the fuel level is higher because the float is sinking. This causes a richer mixture which could cause what you describe because a hot engine needs less fuel. Also accelerating quickly causes the fuel to move in the bowl so it can flood the engine. But other things can do it too - a mechanical advance sticking a little if you have one, an ignition system or ignition coil breaking down with the higher compression load, tight valves causing issues when it is hot, a set of the rubber boots on the manifold cracking, the heater section of the intake manifold rotting thru, electrical wires shorting out - even a loose connection causing weird things. The normal procedure for me on my 1971 bus when I owned it was to inspect the dual port boots, do a valve adjustment, check/smell the oil for gas in it, change the oil if needed, then go thru each system starting with the ignition to be sure it is 100% tip top shape. That includes checking points, plug gap, wire tips for corrosion or failure, lookin for halos around the wires in the dark, feel how quickly the coil heats up when the engine is running, check the timing advance (both the can and mechanical) with a timing light and mighty vac, inspect hoses, wire connectors, then I move onto the carb.

One big clue you can look for - does the engine spit back when you floor it or does it just die? If it spits back and pops then it is likely to be a lean mixture. If it just dies then catches it is likely to be rich IF THE A/F mixture is involved and it is not something else. My 1973 Fiat 124 started dying one day in very similar conditions to what you describe. I pulled the choke out to see if it had an effect and it helped. When I got out to see why it might be happening I happened to just glance down at the distributor while I was headed to look at the carb - low and behold I noticed that the wire for the primary set of points ( it had two sets, one when the manual choke was pulled and one when the choke was off) was grounding against the firewall. That was killing the engine every time I accelerated hard. The choke made it better because it was running on the other set of points. I put something around the wire as a temp solution and things were fine. Recently my lawn edger did the same thing. After I finally pulled the carb to rebuild it - I realized one of the jets had come loose and fallen off. That is all that was wrong with it. We all get in a rush to find the common causes but sometimes it can be other things. My 1971 bus did what you describe and it was the rubber dual port boots. One had cracked and I couldn't see it because it was on the back side of the boot.
Thank You -

Merlin The Wrench

Machine Work/Shop Recommendations: http://kentcomputer.com/77VW/machinework.pdf

Pointers on rebuilding an engine: http://kentcomputer.com/77VW/rebuilding_a_vw_engine.pdf

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vwlover77
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by vwlover77 » Tue Aug 01, 2017 6:57 am

Amskeptic wrote:
Sat Jul 22, 2017 9:55 am
I am pretty sure, Don, that you are actually flooding it. Experiment with me.

Warm engine, set mixture to a 25 rpm drop-off lean condition (it is subtle when the tach/dwell meter is dancing all over the place, but you can hear it too)
Reduce the accelerator pump movement by one increment.
OK, true confession first: I'm running a 132.5 main jet versus the original 127.5 that was in it when I bought the car in 1990. Have been for years. It has always seems happier with this jetting.

I have not been able to thoroughly test with a hot day long drive, but I believe your suggestion fixed it. The idle mixture screw was out way past the 25rpm drop off point, and the accelerator pump linkage is now set to minimum volume. No full-throttle bog cold, no full-throttle bog hot, just some hesitation in normal acceleration for a few minutes during warmup after the choke fully opens. It goes away after the engine is fully warmed.
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Amskeptic
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Re: More Carb Woes - 34-PICT3 on '71 Super Beetle Autostick

Post by Amskeptic » Tue Aug 01, 2017 10:45 am

vwlover77 wrote:
Tue Aug 01, 2017 6:57 am
just some hesitation in normal acceleration for a few minutes during warmup after the choke fully opens.
It goes away after the engine is fully warmed.

That is known as "perfect".
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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