67 Bus, Advance & Timing

I'm a total novice with engines and everything I know about this bus I've learned from google in the last 5 days. Regardless, I've taken this project on and did manage to fix my initial problem with stumbling during acceleration. However it's opened up a new can of worms that I'm trying to fix properly.

As far as I know it's a 1600 engine, with a 34 Pict-3 carb and a bosch distributor with a single vacuum (so it's not the 009). I've set the timing 3 different ways and gotten 3 different sorts of input from 3 different sources. I want to make sure I've got it right so I don't blow this beautiful bus up while hurtling down the freeway.

1) I set the MAX ADVANCE (with vacuum hose off and plugged) at around 3400 RPM to 30º with a timing light. At that setting the idle advance was ~ 1/2" ATDC(!!) My local trusty mechanic seemed to think my advance was WAY too early when he checked my work statically.

2) I set the IDLE ADVANCE (with vacuum hose off and plugged) at 7.5º BTDC with a timing light. Wouldn't that further increase my MAX ADVANCE beyond the 30º that are recommended? Scared of burning this thing up and the guys at vw-resource.com say setting it at the MAX ADVANCE is much more important. Again, it'll idle around 1/2" ATDC if I do that.

3) I set it STATICALLY (with vacuum hose on, not that it matters) to 7.5º BTDC. Same problem as above. Worried about the MAX ADVANCE being too high. The guy at the local VW salvage recommended setting the MAX ADVANCE to 30º with the vacuum hoses attached just to make sure I never exceed the recommendation and/or pre-detonate and blow it up.

I THINK it's an SVDA distributor but it could be vacuum only. How can I tell? I'm totally winging it here and my Muir (idiot guide) should show up in a few days but being a bit obcessive I want to figure it out now and want to know who I should be listening to.

Reply to
OldCoyote
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Look at the distributor and post the numbers stamped into the housing.

Do not confuse total no-load timing advance, vacuum AND centrifugal, with what total advance will be going down the road. If you have a SVDA, single vacuum and centrifugal advance, then the vacuum advance goes away when you reach half throttle DRIVING down the road under load.

Until you post the dist number you have, my guess is that max centrifugal advance will be 22 to 25 degrees. Add on the 7.5 initial timing and you are still in the correct ballpark of 29-32 total degrees. And to get max centrifugal degrees, you need engine RPM's up around 3800.

As an example, here are the specs for the SVDA dist that most parts places sell as the real Bosch one [not the Bruck]: Beetle 1974 * 1600 Federal Manual Trans

Distributor: VW 043-905-205, Bosch 0231 170 034 Can Use: VW 113-905-205AL, Bosch 0231 146 101, VW 043 905 205 ZB (Mexico) (See Note Below) Vacuum Can: 07 059 Timing Set At:: 7.5deg BTDC @ 800-950rpm w/strobe and w/single vacuum hose disconnected and plugged Advance/Retard Range: Vacuum: 8-12deg Adv; Centrifugal: 7-12deg @ 1600rpm,

20-25deg @ 3800rpm NOTE: Volkswagen (with Bosch's help) now makes this distributor in Mexico and is available brand new and ready to install. Do the math: 7.5 initial + 8 -12 vacuum + 20 -25 cent = 35.5 to 42.5! This is correct. Do not worry. VW designed the engine to run with this much advance. Just remember that vacuum advance is there with NO load. With a load on the engine above half throttle, the vacuum signal goes away.

Reply to
Karl

And you should get the Bentley manual. Muir wrote wrong things! It is good reading while you are in the crapper, just don't rely on it.

Reply to
Karl

This is WRONG, for any but mechanical advance -only distributors, such as the 009. So forget about setting it according to max.

Hose off and plugged, set at 7.5, is close enough. I believe this is correct for your carb & distributor combo. As long as there is only one hose fitting on the distributor, and you get the vacuum signal from the LEFT side of the carb. (No other parts matter). Do not take vacuum from a port you may or may not have facing towards you on the carb. If there is one, plug it. That's for dual vacuum distributors.

A vacuum advance generally allows for much MORE advance under light load (part throttle and cruising) than a mechanical -only distributor. When you open the throttle more, the vacuum drops and the ignition advance is reduced, making it safer to put heavier load on the engine. A 009 can't react like that due to lack of vacuum sensing, so it has to be adjusted to "worst case scenario" (your #1 alternative). It is not uncommon to see over 40 degrees of max advance on a vacuum assisted distributor, but it won't happen under load or with big throttle openings. Call it a safety feature and a trick that saves you tons of gas and gives you better response at small throttle openings.

When adjusting a vacuum only or vacuum+mechanical distributor, MAX advance is totally ignored. It will fall where it may, don't even think about it. The distributor will know what is safe, under any conditions, as long as the baseline is set correctly. Usually at 7.5 deg BTDC.

DUAL vacuum units are set at 5deg ATDC because the other vacuum hose generated RETARD. If you only have one hose connector on the distributor, you don't need to worry about that.

Vacuum only distributors are short. The big part of the metal body is only about 1.5 inches tall.

All stock type distributor housings that have a mechanical advance system in them, with or without vacuum, look the same. The body of the distributor housing is taller, to make room for the centrifugal weights. It's roughly 2.5 inches tall.

And lastly, you misspelled Obsessive.

Hope this helps :)

Jan

Reply to
Jan Andersson

So it sounds like both you and Karl are recommending options 2 or 3. Setting the Idle advance at 7.5º (~900RPM and assuming its an SVDA dizzy) with the vac port on the carb blocked and letting the max advance fall where it may. The vacuum and centrifugal advance systems will take care of it and prevent me from becoming a comet. More and more folks are starting to recommend this, including my trusty mechanic. Only folks using the 009 and the guys at

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are using the max advance technique.

Before I knew about timing I was blissfully unaware. I now know enough to be dangerous and scare myself.

Reply to
OldCoyote

Just for the info, what is your dist number?

That is what you set your timing to.

Reply to
Karl

Ummm What about the Type 4 (or '72+ Bus) engines? Does the timing get set like the Porsche 914-4 engines at higher than idle rpms?

Time it the way Jan says.......but I am not totally familar with the Busses, only having worked on a few of them in my younger days.

Reply to
dave AKA vwdoc1

Reply to
OldCoyote

Look around the base for stamped-in numbers, not a plate.

As an example:

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Reply to
Karl

It finally stopped pouring rain here so got a chance to pull the distributor off and have a look.

Z43

0231 168 015 043 905 205L

From what I can see it should be set for 7.5º BTDC with the vacuum hoses C> Look around the base for stamped-in numbers, not a plate.

Reply to
OldCoyote

If the carb was adjusted properly, there should be little or no vacuum advance at idle. It suddenly peaks with very small throttle openings.

The reason to adjust timing with the hose disconnected, is to eliminate the possibility of poorly adjusted carb sending vacuum signal out to the distributor when it isn't supposed to. (34pict series)

Jan

OldCoyote wrote:

Reply to
Jan Andersson

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