Pdsit 32/34 fine tune...

[Davy_B.]

Just installed a set that was overhauled by a company nearby. (Belgium) Concerns a 2l GD (injection) from 76' replacement for the 1.7l from 72' Supposedly everything was transferred to this engine from the top! (Po) Currently I can drive but have some reservations. I adjusted the pdsit's the colin, ratwell, Bentley way! thank you all in advance.... i just read too much i guess!

distributor is DVDA:
bosch 021 905 205 E

currently at:
870 rpm idle 5°ATC
3200 rpm 28°BTC

valves are set to 0.15 intake and 0.20 exhaust. probably should be 0.15 too??? big difference?

fix:

a) At low rpm a hesitation. especially after standing still for a while....

b) The exhaust pops slightly but i still need to plug a leak in the flange of the exhaust. Or they are a little too rich? Currently 3 and 3.5 off on the mix screw?? To see no difference on the test mix hose.(colin way) Valves?

c) I am still missing the burst at cold start on fast idle. I had them tuned to 0.6mm according to Bentley. can i set it more? Bentley said no more...

Both throttle plates don't open equally now but isn't that normal if you adjust the 10mm nut (72') AFTER synchronizing the crossbar to synchronize the airflow at 2500 rpm?
Then you change the position of the throttle valves, right? At idle rpm right does have much higher airflow than left??? cis??? Do you have to fix this with the throttle stop screws??? right is only tuned to 0.10mm as Bentley suggested, so i can't turn much in there. And left i will then presumably plug a hole as airflow increases.... Got me a STE BK sync now so I'm doing it all over.
still have some learning to do but hopefully we will get there!

[67rustavenger]

A slight language barrier.

Sync the carbs with the engine warmed up. They should flow the same amount side to side.
Then sync the linkage so both carb throttle plates open evenly and at the same time.

Since you like to read, read the first 20 pages of this thread. While it concerns wideband results. It does offer very good tuning idea's for dual carbed engines.
https://www.thesamba.com/vw/forum/viewtopic.php?t=293837
Even if you don't have a wideband, it will help you understand getting dual carbs setup and running well.
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[SGKent]

once you get them synced, you can cup your two hands together like you were going to strangle a carb, then bring your hands in to cover up the top. If the RPM goes up as you get your hands closer then the mixture is too lean. If the RPM falls as you bring your hands in, the mixture is too rich. Your hands are acting as a choke. you should be right on top of the carb almost before the RPM starts to fall from your hands cutting down the airflow and richening the mixture. The sync them again.
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[busdaddy]

Idle synch is different than cruising synch, that 10mm nut sets the cruising synch, the individual stop screws adjust the idle. The book settings are really just a starting point, rebuilt or not they are 50+ years old and worn in places, if the high idle isn't high enough add a turn to the choke links, but try the rich/lean test SGK suggested first, if it's super rich (or lean) the high idle cam may not be able to compensate.
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[Davy_B.]

Ok I will definitely try this method!
How would it be that the sync at high speed is the same but then when I look at low rpm there is a big difference in airflow between left and right. Surely you would think that this should not give a big difference anymore? Bad uni-syn??

I'm going to plug the exhaust leak first. Then the valves in/out 0,15... it's not 74' so why I did 0,20 God knows... Hopefully the "popcorn" of the exhaust is already a lot less! Then I'll just redo the procedure with the STE-bk instead of the uni -syn. Hoping for the right result!
I will keep you informed.

[mikedjames]

I once was asked to look at a dual carb setup like this and found the linkage one side had two badly worn heim joints, so there was about 1/8" of slop.

This bus was set for balanced air flow at idle, using the end stop screws, but one carburettor would open well before the other - if I put my head half way between them with the engine idling and blipped the throttle with the air cleaner removed, you could hear the "cough" as one side opened up well before the other as an interesting stereo effect..

I confirmed it by turning the throttle spindles one at a time and discovering that one side was properly connected to the linkage, and the other side was not .
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[Starbucket]

Step one is to sinc. the linkage, hold two plastic drinking straws lightly (one on each butterfly) and have a helper SLOWLY start to press on the gas pedal Don't open the throttle all the way you are just feeling that each carb. is starting to open at the exact same time, if not adjust the linkage (loosen the linkage to the one that opened first) until both open at the same time.
step two is to look down the carb. throats as your helper SLOWLY starts to press on the gas pedal, the accelerator pumps should start to squirt a stream of gas down the carb. throat AS SOON as the throttle starts to open or adjust the pump linkage until they do.
Take a drive and if all is not fine work on your mixture/timing.

[wagen19]

[Davy_B.]

Exhaust leak is bigger than thought. Of both front exhaust pipes, all 4 gaskets are leaking and the flanges are deformed.

[airschooled]

3.5 turns out on the carburetor mixture screws sounds like a lot. When I get these dialed in with Colin's instructions, I find them about 1.5-2 turns out at the carburetor and four turns out (or more) at the central idle mixture.

870 RPM isn't helping you. The closer you get to 950-1,000 with the CIS adjustment, the smoother you'll be driving.

Cold start speed is set with the hex nut linkages off the choke. The closer to the end of the threads your assembly goes, the faster your cold start will be. Cold start enrichment is set by twisting the choke elements. The amount of enrichment affects the speed setting, so set the choke flaps to open in sync and close enough for your climate, THEN move on to cold engine speed.

Of course, you will never get perfect cold idle without working distributor vacuum. It looks like your tests are good, but you also need to test maximum vacuum advance when revved (up to 42°btdc is fine.) Without working vacuum advance, cold idle and throttle response will suffer. Also, test vacuum retard by pulling off that hose at warm idle. Speed should jump up.

Good luck,
Robbie
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[Davy_B.]

[airschooled]

[Davy_B.]

Checklist...

Today exhaust leak repaired.

And gave fast idle links a turn up! 1st test better... Tomorrow more testing!

[busdaddy]

Excellent!, stuff like this is a marathon, not a sprint, keep dealing with a little at a time.
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[Davy_B.]

When should my vacuum advance take effect? And how can I check that. Retard seems ok.

Set my idle at 950rpm and my fast idle links 1 turn up. Much better at thé moment.

[germansupplyscott]

The advance should overtake the retard just off idle. So your timing should be able to get to 8°BTDC and then keep going up, as soon as you open the throttle. Retard should only be in with the throttles closed. So it's a pretty big swing in timing right off idle.
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[airschooled]

You can check it by watching the timing scale with a strobe light while revving the engine. Like Scott said, timing should jump up 10-20° right when you open the throttle.

Another way is to hold the engine at 1,500-2,000RPM and connect/disconnect the vacuum advance hose while watching the timing light. The timing (and probably engine speed) will jump up when connecting the hose, and down when disconnecting.

When EVERYTHING is perfect with your choke and fast idle adjustment, the vacuum advance will be activated at cold start by the fast idle linkage holding the throttle open until the chokes warm up and open fully.

Robbie
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[Davy_B.]

Ok so if I remove retard when i'm at 2000rpm it should not change on the Strobe.

But when i remove vac advance I should go down at 2000rpm.

[airschooled]

[lil-jinx]

at 2000 rpm most of the advance is from the centrifugal advance,you may not see a big drop in timing removing the vacuume,it depends on how open the throttle is,wide open there is very little to no vacuum advance,as throttle closes and the rpm drops then vacumm advance come in play and the weights go to their rest position.when the throttle is fully closed the retard vacuum comes in.
thats how i understand it.
the vacuum timing will behave different under high idle (high rpm with no load) as opposed to the same rpm under heavy load,because the throttle will be more open under load resulting in less vacuum .
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