Stock dual carb setup, '78 auto Bay. All in the timing!

[mcdonaldneal]

I'm starting a thread to run through this carb setup partly as a record and mostly because I had great trouble last year, which turned out to be related to vacuum leaks, and after an engine rebuild this year they were set up 'ok' but with some problems.
I expect to run into some issues, (I'm still very much a novice, but learning all the time! ) I've always found Samba comments great at pointing out the obvious things I've missed, and stopping me giving up!

The stock setup is slightly unusual, in that it is a 1978, 2000cc bay window camper, with twin Solex 34 PDSIT carbs (stock Euro/Aus) with 010 Automatic transmission.

I'm following the factory dual carb setup procedure, beautifully described by Colin (Amskeptic) here: http://www.itinerant-air-cooled.com/viewtopic.php?t=7767 as well as Bentley and Haynes.

Specs on the carb are: Venturis 26mm, main jet x135, air correction 160. The carbs also have the (? Auto only) thermostatic plug to reduce the accelerator pump squirt above 70F (brass thing next to float bowl drain plug) and hot idle valves.
The jet sizes are different from the Bentley specs for '74 (x130, 175) and once I get through the standard setup I could change those if needed, based on wideband readings (I have a standalone innovate meter).

So, what do I want?
Easy starting, smooth choke operation without the engine racing away, steady idle, acceptable acceleration, 70mph on the motorway and 25mpg! (Dream on!)

I'll leave the first post there, to set the scene! Comments and suggestions on the way through are very welcome, although liable to be ignored!

'Till later,
_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

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[mcdonaldneal]

So, what problems have I got?
On startup, with the chokes open just a crack when cold, she catches fine but the engine does race very hard and so I need to knock it down with a blip on the throttle. (The automatic doesn't really like going into gear at 3000 rpm!)
Settles down to a nice idle when warm, with good driveability. However, the large air bypass screw is all the way in to achieve this.
When hot, the idle is too fast.
Fuel economy is poor. 17-19mpg imperial (14-16 US). I realise I'm not going to get 30mpg out of a 35yr old camper, but I've had better than this!
I don't know how tuning for economy would work as there is no idle jet, but it's running with an AFR of 14-14.5 at light cruise and 13.5-14 at WOT. Maybe smaller main jets and if needed, smaller air correction jets to keep the mixture rich at WOT? That's all for later on.

What have I done so far?
Basics are almost right, but I'll fine tune them today. (Valve gaps, dwell, timing)
Potential vacuum leaks? The central idle circuit hoses have been renewed, the connection to the left carb now has hose clips on, the brake booster elbow on the right is original and uncracked, but on the left has been replaced with a length of hose. I've ordered a 90deg elbow though! It's visible bang in the centre of this pic.

The carbs were sent away for a service 2yrs ago, but I've taken them both off, partly disassembled and cleaned and blown everything out. Main issues were a dirty thermostatic accelerator pump valve and hot idle valve. I also punched bigger holes in the hot idle valve gasket to make sure it could work freely.

Carbs at least look clean now! I've set the mixture and bypass screws all out 2.5 turns, and set the throttle plate gap to 0.1mm (0.004").
The throttle plate actually has a hole drilled in it. Does that mean the gap should just be set to zero, does anyone know?

Today I'll refit them and start the setup procedure.

_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

So...
Checked the throttle gap with the choke closed as per Bentley. Should be 0.7mm. It was about .65 so I've left it for now.
You can see the hole in the throttle plate. Does anyone know if that is specific to the Automatic, and whether I should still have the 0.004" throttle plate gap that I set with the carbs off (choke open)?

I fitted the carbs and reconnected the electrics and vacuum lines and went for a test drive...
Appalling! Raced at idle, ran like shit, shaking and low on power. Feeling despondent I looked in the engine bay and saw this...

I'm happy to share my schoolboy errors with you, and you will see the right throttle linkage hasn't been connected back up!
Runs much better with both connected!
Then looked at the points gap. Dwell was 56deg. Adjusting the points gap I find super awkward. At least I have an access hatch! After much fiddling, ended up with dwell of 44deg, perfect! Came in for breakfast.

_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

Ok. Making a little progress and posting as I go, before I forget what's happened!
I have a Distributor with vacuum advance, no retard, so I checked timing at max mechanical advance and it was 32deg or so (Prob after altering the points gap?) Set it so that it was 28deg max advance, which meant 2deg at idle. Ok according to Amskeptic.
Then the high speed airflow. The flow is right at the top of the range of my cheapo 'snail', but they seemed similar and I just made a small adjustment to the right hand control rod. Idle airflow identical (once I warmed up the engine properly!)
Synchronised.

Now,
I've moved on to the mixture. Using the reference hose method, and with both throttle mixture screws out 2.5 turns there was 'no change ' on taking a finger off the hose. Good.
When I disconnect the left cut off, there is no change in idle speed. Disconnect the right and it drops to 600rpm. Both cut off solenoids are clicking with power, so I don't understand why disconnecting the left makes no difference? I weakened the mixture on the right (screwed in) about half a turn, but there is still the same situation.
Does it mean that the CIS is still providing fuel?

I'm not sure how to proceed, so I'll have a think and see if any of you have any ideas?
_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[Slow 1200]

do the throttle shafts have play? in this day an age every PDSIT does and they are a major vacuum leak!
I got my carbs (auto type 3) rebushed and it's a night and day difference

[FreeBug]

First, set the timing perfect, with the idle stabilizer shunted. Without timing correctly first, you could go around in circles

.Take the engine's compressions, too, to save wasted time. If they're ok, proceed with carbs

Then, rebuild the carbs. Even if they were rebuilt two years ago, they still apparently needed a good cleaning... This is the perfect opportunity to check float level washers and level, whether check-balls are where they should be, if all the membranes and gaskets are intact, etc... Check for leaks around the pressed-in aluminium plugs around the shared idle circuit, last ones I saw had the venturi screws missing, with the vents free to flop up and down... Go over them with a fine tooth comb, they might also need rebushing, as Slow 1200 says.

Make all your idle adjustments with the linkage disconnected.

For the throttle opening, make sure your throttle plates don't engage the progression circuit, on both, then install, the set idle with reference to RPM and snail gauge, knowing you should not open either one any more, just lower one or both to match.

For fuel, I won't even try to do anything without access to a gas analyser. It becomes a circular process, reducing fuel on both carbs equal amounts, and compensating with the central idle circuit, and going around again several times. All of this is lost time if you haven't set timing properly first.

In the end, with the gas analyser, you should see equal reactions to equal adjustments on both sides, and be able to do all the fine tuning with the common idle circuit, to get within smog values.

All in all, it can take up to an hour or more, just to find proper idle settings. Then, just check that there's no change in values, rpm, when you connect the linkage back, then check again with the snail, with the throttle blocked at 1500 rpm or so, then check with the snail that they are still balanced when you let the idle rest again.

When they're cold again, you must adjust the fast idle setting equally on both sides, and you can also watch the chokes open and balance the thermostatic thingys so they open equally. There's a 2.3mm on type 3 and 2.6 mm gap on type 4 IIRC (foggy-check that!) base setting for the throttle-stop gap with full choke.

Leave any of that out, and you WILL get overtaken by mopeds...

Hope this helps.

[mcdonaldneal]

Thanks both. That's given me a few things to think about/ rule out.
Slow 1200, there's no real play in the throttle shafts.
FreeBug, timing was set with vac advance disconnected. When you say 'idle stabiliser shunted' do you mean disconnect power from the Central idle circuit? I didn't think that would make a difference, but I can try.
I did pretty much take the carbs right apart. Float level is fine, accel pump is delivering correct volume and choke diaphragm is working. Everything else is in place.
I DID forget to disconnect the linkage when doing the idle adjustments, so I'll check that again tomorrow.
I do have a wideband meter for AFR, but I wanted to adjust without first,then fine tune. But... I got myself tied in knots today, so see if you can make any sense of this.

With the idle circuit power disconnected the mixture hose test suggested it was still a bit rich, and it would still idle with both mixture screws all the way in!
I connected the wideband and the AFR was rich (12.5-13) even with the mixture screws only 1/2 turn out. I wondered if the throttle plate gap was the problem, so I closed them both one full turn- no difference, so set them back.
Finally, with the left mixture screw 1/4 turn out the AFR dropped! I ended up with both mixture screws about 1/8 turn out which gave an AFR of 15. The rpm didn't change much if I disconnected either cutoff solenoid.
Then I reconnected the central idle circuit and blipped the throttle. There was no change in rpm or mixture even with both CIS screws all the way in. Odd.
Then, as it was idling, there was loads of smoky exhaust and some backfiring. (The AFR jumped up to 20 at that point)
I then undid the idle circuit screw by two turns each and went for a drive. Fine on the road, but when I pulled over at idle the AFR was 20 in Drive and 18 in Neutral.
After screwing the idle speed screw in half a turn and the idle mixture screw out half a turn and driving some more the idle AFR was 16, so I did it again and ended up at home with the idle AFR of 14.5 (with everything connected up).

I know that's a long rambling description, but can anyone make any sense of it?
Questions:
Could my mixture control screws be buggered? Surely the idle mixture shouldn't be rich with them so far in? Or is there fuel coming in from somewhere else?
Why don't the idle circuit screws seem to have any effect on idle rpm?
Should I just redo the idle adjustments with the linkage disconnected?
Does smoky exhaust mean rich mixture, like I had at some point today?

Should I just be happy if the idle AFR is 14.5 and she drives well on the road?

Exasperated, and a bit depressed.
_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

Also!
Probably totally irrelevant, but I noticed that the throttle plate on the left carb had beads of ?fuel on it when viewed from above, and the right one didn't.
No idea what that might mean!

_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[FreeBug]

You get no change in idle with adjustment of idle fuel on the carbs? There's two places the fuel can be coming from: the common idle circuit (but you say, if i understand correctly, that that circuit is disconnected?

More likely: take off the carbs and make sure the progression circuits aren't being solicited.

Not likely, but possible: lack of check-ball, really bad installed height of the accelerator pump jet.

I would take off the carb tops, check fuel level , then empty the carbs and flip them over, check the throttle setting. Forget the 0.7 mm setting, make sure those ports are covered! The engine should not idle well without the air and fuel from the common idle circuit.

Timing: there should be a little black plastic square box with wires coming in and out from underneath, placed on the left-hand side. Sorry, my bad, I see on baywindows it is only the very last model that had it although it is on the vanagons.

[FreeBug]

With the common idle circuit disconnected, and with the carb idle fuel turned out 2 and a 1/2 turns, idle should be around 500-700 rpm, and between 3% and 5% CO, and there should be an equal drop in rpm when you disconnect the right and left side idle cut-offs. This is from the Bentley.

[W1K1]

what is your fuel pressure?
if the carbs were rebuilt you may have new needle valves that don't seal worth a damn. My stock fuel pump will put out 7.5 PSI with one stock gasket under it.


My buddy had to dial back his fuel pressure to 2.5 psi or the one carb would be pissing fuel. when it's running at idle the fuel may only be a drip, but when you get on the gas it could be a shower. which may be why adjusting the screws makes no difference on that side and your fuel mileage is poor.
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http://www.thesamba.com/vw/archives/manuals/jim_martin_engine_build.php

1973 super
1965 squareback 1500E
1971 bay window westy- subi swap

[FreeBug]

You'll know if there's an issue with fuel pressure when you check the fuel levels...

[mcdonaldneal]

Ok, thanks to everyone, all good food for thought (and action)!
Looks like I'm in for a bit of disassembly, and I'll recheck the fuel levels. Quick question: is it possible to do that with the carbs in the vehicle, or is it really lots easier just removing them?
Certainly, the throttle plate gap (0.1mm) was not exposing any holes in the throttle body when the throttle was closed
Also, Because the throttle linkage was still connected when I did the idle adjustment could that have been opening the throttle plate and making adjustment impossible? It didn't mention it in the instructions I was using, but I think that's correct?
I should have a go at adjustment with it disconnected first anyway.

Apologies for my ignorance, there's a lot to take in! Thanks to all for your patience!
_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

[mcdonaldneal]

Interesting.
Took the bus for a run and started trying to do the idle adjustments. Linkage off.
Idled at 1000rpm even with central circuit disconnected!
Took the top off the left carb. Float level 13mm.

Looked at the bottom of the carb. Despite the throttle plate opening being less than 0.1mm (you can see the 0.1mm thread caught in the plate), one of the holes above the mixture needle is exposed. So I undid the throttle plate adjustment screw, and tightened it just past contact (90deg past). There is really no gap in the throttle plate now, but the tiny hole is not exposed (last picture). I'll reinstall, check the other carb, do the same and report back.
Fingers crossed!

_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

Did the same on the right carb.
Before and after...

_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[FreeBug]

Hmmm, whodathunkit?

[mcdonaldneal]

[mcdonaldneal]

Ok. I need more help here!
I'll try to summarise where I've got to, and I be really grateful for suggestions.
Sorry for the long post!

Preliminaries done. Valve gaps, dwell, timing, potential vacuum leaks, chokes adjusted cold.
Carb float level good, needle valves working, accelerator pumps working, throttle plate closed so that the tiny ?progression holes are obscured.

Starting point, both mixture screws and both idle screws 2.5 turns out.
Bus drives like this. A little sluggish, but drives.
Idle 900rpm, AFR 12.5 (a little rich)
Disconnect central idle system (CIS). rpm drops to 500, almost stalling.
Turn in mixture screws up to 1x turn. AFR climbs to 13.5 but no more.
Reconnect CIS. Blip throttle. Won't idle. Will run with gas pedal, but as you gradually lift off to idle the AFR gradually goes super lean (18+), then engine dies.
Can only get an idle if the mixture screws are set 2.5 turns out, with AFR 12.5 (CIS disabled). With CIS back on, the idle circuit screws do nothing, and there is no sucking noise from the CIS air intake.


So, with the CIS disabled, I cannot get the mixture weaker than 13.5, but in fact the car won't run unless the mixture is richer than 12.5. Also, there is almost no drop in rpm if right or left cutoff is pulled.
At some settings I could hear the CIS sucking, and the big idle speed screw would alter the rpms, but the idle mixture screw did not alter the rpm or AFR even when screwed right in.

Mostly, if she will idle, she will drive, but always quite rich (AFR 11.5-14 but generally 12). Nothing I have done will result in lean settings at idle or on the road.
Incidentally, at wide open throttle the AFR is 13.5, but one one test run for some reason that dropped to 11.5 and the acceleration was noticeably better (as you might expect!)

Questions:
Any suggestion why it always seems to be rich at idle, even with the throttle plates virtually closed (and the linkages disconnected)?
Why can't I find a setting of the mixture screws that allows me to adjust the idle speed and mixture with the idle circuit screws?
I don't like that it's running a little rich even at my best efforts, but is AFR of 12-14 in normal driving ok, or will it foul everything up?

Any other comments or suggestions welcome. I'm feeling really frustrated that I can't get this adjusted better.
_________________
1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[busdaddy]

Sounds to me like a couple of problems, the sometimes sucking noise from the CIS is often a weak solenoid that only opens when the system voltage gets high enough, a thinner washer under it often cures that.
The lack of response from the mixture screw and extreme rich idle sounds like the air circuit (emulsion) in the CIS is blocked somewhere with more of this stuff:

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