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Idle adjust on 34 PICT-3 FAQ
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wcfvw69 Premium Member
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PostPosted: Wed May 02, 2018 7:44 pm    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

Who.Me? wrote:
busdaddy wrote:
Everything you describe now says you need to close the choke a little more.
The choke breaker should crack the plate open by itself as soon as the engine starts, it's that small spring loaded diaphragm with 3 screws that faces the rear. If it's ruptured or the top of the carb is warped so the gasket doesn't seal it's vacuum passage all sorts of odd things can happen.


I tried closing the choke completely again and it made the cold idle worse. It basically just died.

I cracked it open and started it back up. I left the housing loose and swung the choke closed while it was idling. It died again. It definitely needs the choke open a little to start and stay running.

It wouldn't run fast enough or long enough to tell whether the choke diaphragm was having any effect, so while I was messing with it, I took the top off the carb and checked the diaphragm. There was petrol on the vacuum side and the shaft was 'sticky', so I took it out, cleaned up the housing and replaced it with the diaphragm from the rebuild kit to be on the safe side.

Will give it another try tomorrow to see if that fixes it.

Thanks for your patience.


Remind us if you're running-

*Thermostat and flaps-
*Stock muffler or aftermarket header
*Working warm air flap in the oil bath via the stove pipe to the oil bath air cleaner.
* SVDA distributor? Which one and how is it timed?
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PostPosted: Sat May 12, 2018 12:08 pm    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

wcfvw69 wrote:


Remind us if you're running-

*Thermostat and flaps-
*Stock muffler or aftermarket header
*Working warm air flap in the oil bath via the stove pipe to the oil bath air cleaner.
* SVDA distributor? Which one and how is it timed?


Sorry, I missed this post.

Thermostat and flaps -yes, fitted and opening and closing correctly
Muffler - stock
Oil bath - warm flap works (can be seen operating in the video below)
Distributor = 043905205 L (SVDA), timed with a light at 30º advance at 3500 rpm

I replaced the idle jet with the 57.5 as VolkzBitz suggested and it was easier to tune. It idled better when warm, but the change hasn't fixed the cold start issue.

I took some video earlier today. Not sure if it will help with suggestions...

This was with the engine stone cold. Idle cut out working correctly. Choke flap set to just closed.

On the first turn of the key after pumping the gas pedal the engine caught and started, but struggled and died after three or four seconds. I tried restarting but it wouldn't catch. It fired up when I gave it gas and revved it up, but it died as soon as I let off. This is the problem I've been having. I've seen other VWs catch and idle fine from cold without being revved, so I can't see why this one shouldn't.


Link
[youtube][/youtube]
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Tcash
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PostPosted: Sat May 12, 2018 2:13 pm    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

I don't know where you are at in diagnosis. But you should always start with a
Tune up

Good luck
Tcash
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PostPosted: Sat May 12, 2018 3:46 pm    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

You say the engine is a tired 1600, maybe oil is seeping past the rings overnight and when you try to start it cold, the oil is fouling the plugs until it gets burnt off? Looking at the video, I would say you need to pump the accelerator a little more as your cranking the engine, and let it rev for a few seconds after it starts by holding the accelerator open.
You also need the correct size hole in the throttle plate, if you just put a rivet in, this would throw all the settings of the carburetor off.
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PostPosted: Sat May 12, 2018 4:06 pm    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

What's interesting to me about your video is when it started and you feathered the gas then let off, it sounded like the choke was not working. Usually the engine idle is up with the choke on as it's running richer due to lack of air with the choke flap blocking the air.
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PostPosted: Sun May 13, 2018 3:25 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

wcfvw69 wrote:
What's interesting to me about your video is when it started and you feathered the gas then let off, it sounded like the choke was not working. Usually the engine idle is up with the choke on as it's running richer due to lack of air with the choke flap blocking the air.


Yes, that's what's confusing me. It only starts to fast idle after it's been revved for 20 seconds or so. It's like the closed choke is starving the engine. It never sounds 'lively' as it idles on choke.

This isn't a new issue; it's been like this since I got the truck, but has been a low priority while I worked through steering, brakes, transmission etc. It does make me doubt the reliability though, so I've not been using it as much as I could.

I tried cracking the choke open a little when I had the old 55 idle jet in and it would catch and run by itself (but slowly) until it got a little heat in to the engine. If I blipped the throttle during that early idle though, it would rev then kill the engine.

VolkzBitz - I hadn't thought of that but I'd expect it to blow smoke of smell like it was burning oil if that were the case? It smells rich at idle, but not of oil. It sometimes gives an initial white puff as it first starts, but doesn't smoke at idle or under load. By tired, I mean compression was 100-110 across all four cylinders when hot when I checked it last.

Tcash - yes I've been through the tuneup process.
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PostPosted: Sun May 13, 2018 3:49 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

I'd circle back to the pop-rivet like Tim is suggesting. How big is the hole now with the Pop Rivet in place? I know the holes has to be pretty close to original size.

If you're choke is closed at start up, it may be struggling to get enough air through the throttle plate to idle due to the rivet hole size. Did you verify that the vacuum diaphragm is working on the choke plate?
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PostPosted: Sun May 13, 2018 4:32 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

wcfvw69 wrote:
I'd circle back to the pop-rivet like Tim is suggesting. How big is the hole now with the Pop Rivet in place? I know the holes has to be pretty close to original size.

If you're choke is closed at start up, it may be struggling to get enough air through the throttle plate to idle due to the rivet hole size. Did you verify that the vacuum diaphragm is working on the choke plate?


The pop rivet hole is the size of the rivet stem, so roughly 1.5 - 2mm (0.06 - 0.08 inch).

I can try taking it back out. The hole in the throttle plate is bigger than the SVDA-distributor hole size though. The plate looks like it was newly installed when the carb was refurbished, so isn't original to the carb.

I tested the choke diaphragm with the carb off. Not sure how to test it with the carb installed though. Should it pull the choke plate open at idle speed, or just when revved?
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PostPosted: Sun May 13, 2018 4:59 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

The size of the hole in the throttle plate for the SVDA is 3.2 mm, I wouldn't go smaller than 2.7 mm. Where did you see that the hole for the SVDA should be smaller than 1.5 mm?
To test the choke pull off diaphragm. Remove the carburetor top, the choke unit and rear cover. You will see a small hole near the throttle return spring arm in the top part of the carburetor that mates up to the lower section. After you push in the end of the choke diaphragm arm that was under the choke, put your finger tightly over this hole and let go of the diaphragm arm. the arm should not move, or move slowly back out. If it returns straight away, there could be a vacuum leak, most likely the mating surfaces of the choke pull off diaphragm cover that has 3 screws. Both surfaces should be re-surfaced flat.
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PostPosted: Sun May 13, 2018 5:12 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

VolkzBitz wrote:
Where did you see that the hole for the SVDA should be smaller than 1.5 mm?


I didn't, I just read that the hole should be smaller than it is on my throttle plate and that others said they've successfully used a pop rivet with the stem removed to reduce the diameter, so I gave that a go.

VolkzBitz wrote:
To test the choke pull off diaphragm. Remove the carburetor top, the choke unit and rear cover. You will see a small hole near the throttle return spring arm in the top part of the carburetor that mates up to the lower section. After you push in the end of the choke diaphragm arm that was under the choke, put your finger tightly over this hole and let go of the diaphragm arm. the arm should not move, or move slowly back out. If it returns straight away, there could be a vacuum leak, most likely the mating surfaces of the choke pull off diaphragm cover that has 3 screws. Both surfaces should be re-surfaced flat.


Thanks, I'll have another look at that too. I'd tested it by sucking on the hole with the carb top off and it caused the choke butterfly to open, but that must be way more vacuum than the air rushing through the carb venturi would generate. I'll try your method.

As before, I appreciate your patience, particularly with the time difference between the UK and US.
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PostPosted: Sun May 13, 2018 8:17 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

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PostPosted: Mon May 14, 2018 9:18 am    Post subject: Re: Idle adjust on 34-PICT-3 FAQ Reply with quote

VolkzBitz wrote:
To test the choke pull off diaphragm...


Just checked it. It holds a vacuum. I gave it 20 seconds or so and it held the arm in until I released the seal over the hole.

I've taken the pop rivet back out for now.

Any other checks that I should do before I put the carb back on and tune it again with the rivet out?
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PostPosted: Mon May 14, 2018 9:20 am    Post subject: Re: Idle adjust on 34 PICT-3 FAQ Reply with quote

I hate this carb with a passion I reserve only for Xevin...
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PostPosted: Fri May 18, 2018 11:04 am    Post subject: Re: Idle adjust on 34 PICT-3 FAQ Reply with quote

Finally...


Link


I cut the pop rivet out.

Unfortunately, after I checked the choke diaphragm on Monday, I realised that the accelerator jet had gone AWOL. I couldn't remember seeing it when I took the top off, but I searched the garage just in case. I couldn't find it so I checked the intake and cylinders with an inspection camera but still couldn't see it. I ended up stripping the manifold off to check it wasn't stuck in behind a valve. Not a sign of it. Either it never went in the intake or it went straight through and out the other end.

Anyhow, after putting it all back together it starts and fast idles from cold and idles warm. It's not the smoothest, but this is the first time it's idled by itself from cold since I bought the truck.

I guess it just needed that bigger idle jet. The pop rivet must have been a step too far.

Thank you all who offered advice.
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PostPosted: Fri Jan 21, 2022 3:23 pm    Post subject: Re: Idle adjust on 34 PICT-3 FAQ Reply with quote

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