Author Topic: 74 auto stick - eratic idle, control valve leaks?  (Read 30 times)

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Offline andk5591

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74 auto stick - eratic idle, control valve leaks?
« on: 11 January 2019, 22:14 »
Been tearing my hair out and got this car drivable and sent home, BUT I need to resolve what is going on when i comes back

74 Super.  1600 DP, correct carb 34 PICT3 with extra port and distributor (kind of - I forget the model, but SVDA ending in 205P I think).  New points, cap, plugs, valve adjustements, etc.  Carb cleaned, adjusted etc, also swapped

Initial problems were linked to leak in intake center section - stalling at idle.  Replaced that and started making progress.  All through this there has never been a shifting problem or is there ever. 

So here is where I am now.  Idle mix adjustment not even close to where it should be.  Probably 6 or more turns out (also dropped idle jet from 60 to 55 with very little change).  When you rev it - the idle stays around 1200 or more for about 10 seconds then drops to 900.  Plus it stumbles when pulling out and almost feels like a slight surging at lower speeds.   You have to almost baby it when pulling out and it then drives OK. 

I have looked for vac leaks everywhere - nothing on the carb, intakes, hoses.  Have also replaced the small and large vac hoses. I even swapped the carb with a rebuilt by Volzbitz a couple times.  Acts a little different, but not much. 

It still acts like a vac leak to me and if I understand the operation of the control valve properly, a problem in the vac can or the servo would only happen when shifting.  So, I think I have a prob with the control valve. Something that we have seen is when revving with the control valve electrical connection disconnected, the idle comes back down much faster (couple seconds)  Any insight would be greatly appreciated.

Offline bhartwell59

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Re: 74 auto stick - eratic idle, control valve leaks?
« Reply #1 on: 14 January 2019, 04:20 »
Have you cleaned/unclogged the heat risers of the intake manifold?

I had a stalling out issue that seemed to defy logic... monkeyed w/the idle and bypass, timing, etc. Wasn't until I cleaned out the intake manifold that the idle stabilized and I could properly get my 34pict mixed right.
1974 zambezi green Ghia vert

Offline 68autobug

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Re: 74 auto stick - eratic idle, control valve leaks?
« Reply #2 on: 15 January 2019, 10:12 »
YIKES..... very odd problem when disconnecting the control valve....
I would try this - put a new wire from the battery via a relay connected to the ignition... to see if that fixes the problem...  or just connect the control valve to the battery while You do this test.  and check Your ignition , points & distributor rotor button....  which can all cause problems...  check to see if You have 12-14 volts...
I would also adjust the carburetor choke so it doesn't work... wide open.-----  for this test. [also take the wire off]
until You get everything running correctly ---
You can seal all the exhaust ports using silastic... silicon... which will take the very high exhaust temperatures.
replace the carburetor inlet gasket & inlet gaskets etc...

A leaking inlet anywhere on a VW engine really makes a huge difference...
A good investment is an electronic ignition like pertronix....  so You set and forget... and never have to replace points again...
or the condensor which can also cause problems...

with the engine turned off, and the key turned on, can You change gears about 10+ times... by moving the gear shifter slightly forwards or backwards....??   there should be enough vacuum in the tank to do this at any time....

Now the gear shifter works by grounding out, when You move the shifter knob... so, the gearbox needs to be grounded with a ground strap which originally was at the nose of the gearbox - front gearbox mount... Make sure that is still there and still grounded... clean both ends etc.... or replace it.... otherwise the ground is the shaft from the gearshifter base to the gearbox.

oil everything that moves on the carburetor to stop any wear and to stop leaks...
have you checked the timing with a timing light or meter to see if it is correct...??? and not moving about...


Lee in Australia
40C degrees today  42C tomorrow... YIKES that is hot.... Lee   68Autobug



-- Helping keep Autostick beetles on the road --
   -1968 Silver metallic 1600 single port Beetle - with BOSCH  SVDA and new BROSOL H30/31 carburetor with GENIE Extractor exhaust system with a quiet thunderbird muffler

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