I've got a 70 145S with B20B engine, and also have '71 volvo FSM which should be pretty good for the '70.

I was sucking on the dizzy vacuum dashpot with a Mightyvac and got no response. Upon reading up in the FSM I was most suprised to read that B20B dizzy has VACUUM RETARD, not vacuum advance which is what I've seen on dozens of other cars I have worked on. Vaccum advance is generally considered to improve driveability and economy at part throttle conditions.

Also, I cannot figure out from the manual where vacuum dashpot is supposed to be hooked up. Does it connect to the normal vacuum port that gets suction immediately upstream of carb throttle butterfly? (I've got the IPD Weber DGV kit and this is the only vacuum port available.)

Can anyone tell me what is up with VACUUM RETARD function???

Should I ditch this dizzy and find one with a proper vacuum advance ???

Also, I've been thinking of converting to elec ign with the Petronix kit from IPD.

What options do you all recommend ?

Thanks in advance !
I'm really enjoying the folks on this forum.

Later,
Al

Actually, I think it is already gone since application of vacuum to dashpot produces no movement of dizzy breaker plate. Somehow it is already locked down.

I keep wishing for one of those fancy timing lights with a degree indicator dial. Last I checked a couple of years ago Mr. Snap-On-Man wanted $400. Too steep. Short of that... Maybe I'll pull the pulley and make marks at every five degrees BTDC up to about 45. Then static timing light would do the trick for the whole dizzy operating range.

Was quite suprised to read in Volvo FSM that up to .008" slop in dizzy shaft is acceptable. That's a lot of variance in points gap and dwell. Fortunately my ol 145 dizzy seems to have maybe half of that for free play. Maybe I'll rig up an indicator and measure it exactly. Prior owner musta been religious about adding the required drippy droppies of oil each 10k miles in funny Volvo dizzy oiler feature (little knob thingy). I juiced it up good with my favorite mixture of Moly powder and Marvel Mystery oil. That should keep 'er going.

Later,
Al

Just to double-check what you have, vacuum retard turns the breaker plate CCW when suction is applied; advance turns it CW.

My understanding is that the retard dizzy was a form of smog control -- it's usual to leave it disconnected if local regulations permit it. If you do hook it up, it goes to full manifold vacuum, not the low pressure port on your Weber. Time it with the vacuum connected, in that case (for vacuum advance hooked to the mainfold, time it with the vacuum disconnected and plugged).

So just to be clear...

I have a B20F with D-jet. I am using a Perlux ignition system in place of the points/condenser. The vacuum line from the little saucer shaped appendage is still attached. I've never been sure if I still needed it (or ever needed it, as seems to be the case.)

It sound like I don't really need it. Is this true? If I unhook it, should I plug the hole on the dizzy, or otherwise modify it?

Thanks-
Eric

If it really is a retard (suction turns the breaker plate CCW), just unhook it and remove the rubber line. No need to plug the hole in the dizzy, but DO plug whatever the other end of the line was attached to.

Phil the factory method of setting timing on the B20 with vacuum retard is to set the initial timing with the vacuum disconnected. To set 10 degrees BTDC with it connected would produce a total advance of over 40 degrees, which is far too much.
Ported vacuum advance, like old Fords, can be set connected or disconnected as there is no vacuum signal at idle. GM and Chrysler are disconnected because they use manifold and the vacuum is present at idle. Exceptions exist in all by the time emission controls happened by though.

Rhys,

I'm sure you're correct about what the manual says, but that doesn't mean the manual makes sense other than for smog purposes. Typically, the centrifugal mechanism provides about 17 degrees advance, and the vacuum 7 degrees of retard. Let's examine how that works with the vacuum hooked directly to the manifold.

Version 1 - basic timing set to 10 BTDC with vacuum disconnected:
At idle (full vacuum) = 3 BTDC
1/4 throttle, low RPM = ~7 BTDC
1/4 throttle, high RPM = ~23 BTDC
WOT, high RPM (no vacuum) = 27 BTDC

All that is too little advance, regardless of the particulars of your motor, carburetion, fuel type, etc. You'll get boggy performance and poor economy.

Version 2 - basic timing set to 10 BTDC with vacuum connected:
At idle (full vacuum) = 10 BTDC
1/4 throttle, low RPM = ~14 BTDC
1/4 throttle, high RPM = ~30 BTDC
WOT, high RPM (no vacuum) = 34 BTDC

That's still very conservative timing for a street motor, IMHO...

I agree with you number Phil except for one thing - distributor degrees (as you say centrifugal mechanism) relate to the crankshaft at twice the amount quoted. My information (Volvo shop manuals for 1972 and 1974 B20B and F) show between 11 and 13.5 degrees centrifugal advance at the distributor, or 22 to 27 degrees at the crankshaft. When added to the ten initial this becomes 32 - 37 degrees at the crankshaft, which is, as you indicate, reasonable for a street engine. Adding the 7 or so degrees by leaving the retard system connected during adjustment would be excessive if it produces more than 40 degrees at the crank.
I have used 10-15 degrees initial (depending on camshaft) plus the amount in the distributor to achieve 35-38 at the crank, and discarding the vacuum system. In fact I silver solder the breaker plates together to prevent any slop between them from varying the dwell.
Rhys

Sure, I won't argue with any of that -- it clearly depends on which dizzy you have, so whatever works correctly is fair. I have not myself had a model with as much centrifugal advance as that, measured in crankshaft degrees -- the retard units I've had were all the older iron-bodied type. (They're long gone, I couldn't give you the part numbers.)

But to get back to the point of the thread, there is NO performance or economy advantage in using vacuum retard at all. I say if you have one, leave it disconnected.

And on that point Phil we are both agreed.

First off I set the timing to factory spec - maybe a degree or two more if gas and carbon build-up will allow it, and disconnect the vacuum retard every time. Its purpose is to reduce peak combustion temperatures and lower Nox formation - sort of an early method before convertors came along. All it did was increase fuel consumption, exhaust valve temperature, and lower power output. Many times I have tuned up customer cars, told them about my little modification, and a year later the car comes in with the damn thing hooked up and the customer telling about this other mechanic who loudly proclaimed "Ya got ta have vacuum advance - evrrybuddy knows thet!" Sure. If only it was.
Originally it was hooked to manifold vacuum on D-jet and K-jet, and to the rear carb on B20B at the port below the throttle plate.

I've found vacuum retard to be more common. The distributor with Bosch number ending in 085 is the only vacuum advance I've seen for B18/20.

They all have centrifugal advance.

What number do you have?

As I understand it, the vacuum pulls the timing down at idle, and at (de?)
compression (when you let your foot off the throttle) to save gas.
I had mine set up this way, maybe I still do...on one of the cars, I can't remember. Anyway, it works just dandy.
You can leave it disconnected (very common) or set it up AFTER you find the timing you like.
You'll probably have to set it up with a PCV line to the manifold to get it to function.
Best,
shayne.