Advance runs on

[John S.]

I've been fighting several things but just about have this down.
Bone stock 1600 DP in a '71 bus.
Idles fine, timing dead on.
Newly-redone 34PICT-3 from Tim and a German distributor with a NOS vacuum can.
Problem: warmed up and idling at 850 RPM if you rev it up the advance goes to around 15 degrees and does not come back.
If I pull off the retard line and plug the carb port same thing. It goes beyond the 7.5 degrees, where it should be. The only way to get it back on the correct timing is to put it in gear and drag it down by letting the clutch out. Or you can shut it off; start it right back up and it is back on the timing mark, idling fine.
I have just totally torn down the distributor and cleaned and lubed it because this was happening. Did I miss something in the distributor or is it something else?
Everything in the advance system is very loose, not binding.
What is going on here?

I greatly appreciate any help.

[busdaddy]

So when you say "bone stock" that means you have the altitude compensator/decel valve installed too?, have you tried adjusting it at all?
Is it a 205Q distributor?, was the number on the can the correct match for it?
Did Tim supply a carb with the correct base number for a 71 bus?, or just rebuild whatever you sent him?
Ever oiled the felt down in the shaft under the rotor?, any electronic conversion units in there that may be too tall for the cap?
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[mikedjames]

Your idle speed is set too fast. This is most likely the throttle plate not closing.

It has to be 850 rpm , as above about 1000 rpm the distributor is providing centrifugal advance.

You will also get some vacuum advance at idle if the throttle plate is not fully closed, as the throttle plate does not properly block the vacuum port.

This can make the idle speed climb up to the point where the centrifugal advance cuts in as well.


The sign of this is that the vacuum advance hose hisses at idle and sucks your finger when you put it over the end. It should not do this.

Then when you fix this you have to do the timing again... at 850 RPM with the hoses off...
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1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[John S.]

Sorry, no decel valve. Long gone from previous owner hacks.
I'm trying to bring this back to good stock drivability.

The distributor is a 205Q with a 853 vacuum can.
The carb from Tim is a 325-3 which I believe is for a 72 "California" manual.

The idle is a steady 850.
I just ran out and checked; no suction on the advance line unless the throttle is open. When it is closed there is no vacuum.

It's not happening now.
Maybe only when it's warmed up?
Could that be a clue?

[John S.]

Sorry, didn't answer all the questions.
I just tore down the distributor this morning in hope of alleviating this problem. Cleaned and lubed everything.

What would electronic units not fitting under the cap cause?

[FreeBug]

If the electronic set-up is bolted to the plate which rotates with vacuum advance, then the wires' stiffness can interfere with the plate moving freely as it should.

[John S.]

OK, this had point and condenser before I tore it down and it was doing the same thing. It may have been the weights sticking as it had some weird crap underneath the weights. That has all be taken care of BUT as a move into the 21st century I installed my first Pertronix set up. It works wonderfully and I knew to trim the grommet and checked for clearance of wires but did not think of the wire stiffness. It did move back and forth when I checked it on the installation earlier today. I can double check that though.

[John S.]

It wasn't doing it when warming up.
I got under the cap and loosened the wires some (don't think it was binding), still OK.
Took her out for a few miles and it is back.
Not hanging up at 15 degrees, now only about 5 degrees BTDC.
The retard is working as when it was warming up, idling at 5 ATDC I pulled the vacuum line and blocked the carb port and she went to 7.5 BTDC.

Is the Pertronix wiring that stiff? Doesn't seem so.
I can keep fiddling with it. This is the only problem at this point.
She runs well with good pick up and engine braking.

[busdaddy]

I've seen some modules a little too fat so they rub on the inside of the distributor body as well.
Also check that you don't have to sand off some material from the base of the rotor, the added thickness from the reluctor wheel can make the rotor push up tight against the carbon tit in the cap, that could theoretically jam up the mechanical advance.

Edit: I know you went through the distributor, but have a look at this in case there's something you may have missed: http://www.thesamba.com/vw/forum/viewtopic.php?t=558307
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[John S.]

Another thought, when I tore down the distributor this morning I had to reattach the little "thingie" that holds the ball on the points plate.
Can that be set too tight? The slot for the screw was slotted vertically, as if it the "thingie" that holds down the ball could be set higher (looser) or lower (tighter).

[John S.]

Thanks, Bus Daddy.
I will let things cool down and take another look at this new-fangled electronic widget. IF this turns out to be the culprit I will curse myself for going away from points (which I have been running in ACVWs since the early 80s).

[John S.]

I looked under the cap and yes, I could see where it is being ground up by the rotor which must be jammed up against the cap with zero gap. Damn, it was brand new too. Checked the cap I had taken off previously and there was no evidence of damage so it appears Sir Busdaddy may be on to something.
If this is not allowing the advance mechanism to return, once advanced, that would be it.
I will dig into this issue in the future. If I need to take some of the bottom of the rotor to heal this problem, that would be a blessedly easy fix.

[FreeBug]

Yes, the attaching tab for that ball bearing can be set too tight, it is just to take out slop, but should be able to turn freely, like a bearing.

loosen it to let the plate turn freely. From your post

[John S.]

It is a DVDA; it is timed at 5° ATDC with both advance and retard attached.
The vacuum retard is about 13° so when I pull off the vacuum line and plug that port on the carburetor at idle it should (and does) jump to 7.5° BTDC.

I think the tight rotor/cap interface is the issue.
I will address that by trimming the rotor.
If that does it, I'm one happy guy.
If not, I'll look again at the ball and socket.

[FreeBug]

Then which is getting stuck with extra advance? is it the centrifical advance or the vacuum?

It sounds like it's the mechanical advance, so nothing to do with a sticking plate or over-tight ball-bearing, or stiff wires, but rather something to do with what you have looked at on the shaft. With the cap off, does it snap back into place, or can you still turn the rotor counter-clockwise after it has come to rest?

[mark tucker]

so is it the rong rotor? bent shaft? loose fitting rotor? cocked cap? rotor not pushed down far enough? always look for interfearance in everything and free movement. Ive never seen wires so stiff it would affect this in any way.but I havent seen it all...yet. I have had rotors that were loose fitting and also addvance plate that was loose from the shaft portion letting them move about 3-5 degrees independently.but usualy not loose but can be moved with slight force,very slight force. also wore pivot holes in the weights or flopy weights can throw another bone in the works. souloution??? a new cb billet dist with the oh so eazy tunable addvance up top or get another dist and go from there and compare and build 1 good one if you are capable of it.(not saying you are or are not, thats not my call, but how many times are you going to eff with it....) there usualy pretty simple when they were built right in the first place.

[John S.]

I believe it is an excellent distributor as I just "went through it" but the addition of the Pertronix points replacement system has added the variable of the magnetic wheel which doesn't allow the rotor to sit low enough to not contact (and drag) on the cap.
Simple solution I'm aiming at is trimming the rotor (mentioned numerous times in thesamba posts). If that fixes the problem I still have original German parts save for the new-fangled Pertronix.

[John S.]

And yes, to answer the earlier question, the rotor snaps back as the weight springs return the whole affair. I checked that after I reassembled the unit.
I will be filing off some of the bottom of the rotor so that it can sit as low as it is designed to sit. I'm believing the theory that that will relieve the rotor/cap interference and allow the centrifugal advance to return via the springs, as God intended. Too hot to do it today but probably tomorrow.

[Danwvw]

The Vac advance on those sets on a plate that has a ball bearing under a little retainer right! It may be the Vac adv that is not returning could be the plate sticking or canister doing it as well.

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[busdaddy]

It's easy enough to rule out stiff wires or tight balls (wooo...sounds dirty), disconnect and plug the vacuum lines to the distributor, make sure the plate is at neutral and rev it up, if the advance hangs it's not the vacuum advances fault.
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Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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