Idle adjust on 34 PICT-3 FAQ

[busdaddy]

[Who.Me?]

Thanks both. I'll try some more tinkering this weekend.

If I need to enrich the mixture at higher revs do I change out the main jet, or does the idle adjustment also sort the mixture at higher RPMs?
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Andy


Looking for info on my truck's history. Are you from Campbell California or nearby. Do you recognise it? ... http://www.thesamba.com/vw/forum/viewtopic.php?t=636786

[kreemoweet]

[wcfvw69]

Visualize the idle circuit in a 34-3 as its own separate carb. Fuel level is critical on these German Solex 34-3's, especially at idle. Also important is fuel pressure. I think I saw your thread where you rebuilt your German square top pump? What fuel pressure is it putting out?

What kind of bus is this? Bay window or split?
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[Who.Me?]

[Who.Me?]

[kreemoweet]

[Who.Me?]

OK, so tried tuning the carb again yesterday to make sure it wasn't just me. I also re-checked the timing. There was a fair bit of scatter around 7.5º at idle, but at >3000 RPM, the timing is pretty steady at 30º (assuming my timing light is correct).

Once again, it seemed to idle OK when I'd finished, but the moment I started driving it, the idle dropped right off again. It wasn't consistently bad though. a couple of times it seemed to idle correctly (I don't have a tach in the cab), but most of the time, the idle sounded very slow and twice it just cut out when stopped at lights.

I pulled and gapped all the plugs this morning. They all look like my earlier photo, so no change from the last time I tuned it.

I pulled the carb and cleaned all the jets (none appeared blocked). They all matched the builder's note.

But - the fuel level was 25mm below the rim. I triple checked this including before and after disassembly and cleaning of the jets. The VW resource notes say the level should be 19mm. That doesn't make sense to me. I thought the level needed to be pretty much spot on for the inrushing air to draw fuel through the orifices. How could the engine even run with the level 6mm below spec? Does the fuel level need to be matched to the holes in the emulsion tube and are there different tubes?

I checked the float and float valve and they're both fine. The washer under the valve is 0.88mm. Could changing the washer to a thinner one fix a 6mm discrepancy? (I recognise that the valve is closer to the fulcrum than the centre of bouyancy of the float, but I don't know how fine or coarse the adjustment is.)

I have a float from an old BOCAR 34 PICT 3 carb that I took off the engine years ago. Should I try fitting that?

I also had a look at the end of the idle jet. It looks OK, as does the seat, but I noticed that the shape of the jet body and size of the holes are very different from the jets that I've bought here. I ordered 2060 jets in 57.5, 60 and 65 sizes to try, but haven't fitted them because they're so different to the g55 jet that is in the carb now. The hole sizes around the sides are much larger, they have a 'shoulder' in a different position and the ball bearing inside each jet is much further down. The jet that I took out is labelled SOLEX. The new ones are labelled RCA.

I've attached photos below - the jet from my carb is on the left in both pictures.

Have I bought or been sent the wrong jets, or are these interchangeable?


Thanks

Andy

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Andy


Looking for info on my truck's history. Are you from Campbell California or nearby. Do you recognise it? ... http://www.thesamba.com/vw/forum/viewtopic.php?t=636786

[kreemoweet]

[Who.Me?]

[wcfvw69]

[kreemoweet]

[Who.Me?]

[SGKent]

normally a saturated float will cause a higher bowl fuel level. It could be that someone used an aftermarket float which has more surface area and sits higher causing a low fuel level.
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[SGKent]

[Who.Me?]

Touch wood I seem to have solved the warm idle issue. It also starts more easily now and will idle from cold without giving it gas, but cold idle is lumpy.

So far I've cleaned the carb jets and sorted the fuel level issue.

I also added a pop rivet to restrict flow through the hole in the throttle plate. (When this carb was rebuilt a new throttle plate was fitted. I used the shanks of some drill bits to check the hole size and it was more than 3.5mm, so it looks like the rebuild kit that was used included a throttle plate for a DVDA distributor. I have a SVDA distributor.)

After re-tuning; the above cured the struggling warm idle issue but it still wouldn't start 'on the button' from cold. Cold idle speed remained very low and it would stall almost immediatley without gas.

On a hunch I changed the distributor cap and rotor arm. Both looked OK, but I noticed that corrosion products built up quickly on the cap terminals.

The engine then 'caught' more quickly, but would stall almost immediately.

I adjusted the automatic choke to crack it open slightly as it's about 12ºC here at the moment (low 50s Fahrenheit)

It now starts strongly and idles at a good speed (better than I can remember this engine idling at cold), but is slightly lumpy.

If I blip the gas during the initial idle, the speed drops right down and the idle becomes quite rough. It's like it's running on three cylinders. I then have to give it gas to keep it running until it warms up a little. If I *don't* blip the gas during that initial stage it seems to warm up OK on its own though.

It's almost as if it needs the choke open slightly to start, but the choke opens too quickly thereafter. I think blipping the gas is allowing the fast idle cam to move and open the choke plate as the choke coil warms, but it feels like the engine needs longer to warm up before it gets that open.

It's not practical to leave it idling with the throttle arm trapping the fast idle cam as the truck is in a garage and I need to get it outside before it fills the garage with fumes.

Any ideas? I can't see how to balance the apparent need for the choke to be slightly open when it cranks over, but to open more slowly than it does thereafter?

I haven't tried any of the larger idle jets yet (it currently has a 55 in it).
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Andy


Looking for info on my truck's history. Are you from Campbell California or nearby. Do you recognise it? ... http://www.thesamba.com/vw/forum/viewtopic.php?t=636786

[busdaddy]

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.
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[VolkzBitz]

Did you try the new idle jets you purchased? Even though they look different to your original they are the same. Your original .55 may have been reamed out too big, try the 57.5 that should work.
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