Ignition timing questions.

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Larry Louton

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Hello, Trying to correct the ignition timing on my 1972 Bavaria, Vin 3103568 with Weber 32-36 carbs and a 123 distributer. The car is missing the emission tag near the washer bottle. How many degrees before TDC with the vacuum disconnected and should the vacuum line be hooked up to manifold vacuum or venturi vacuum? Should the timing be set at idle or at a specified RPM? I have found the window on the bell housing and the marks on the front balancer.
Thank you.

Larry Louton
 
22 degrees BTDC at 1700 rpm. Plug advance hose after pulling from dizzy, it is on the pyramid side of the can. Advance hose comes from above throttle plate so it actuates only when throttle is opened. Retard hose is below throttle plate (manifold vacuum) and comes from flat side of mechanism.
 
Hello Chris, Finally got back to working on car, Found first the question of removing the gas cap the tank would go woosh? Vacuum fitting on rear intake had been removed and brazed shut with a golf tee in hose. Hose fitting now has new pipe. Smoke test proves flow to tank now with wisp of smoke out of charcoal side of canister. Removed fuel tank sender to inspect for crud in tank. Looks very clean, New seal on sender, The distributor on this car has only a vacuum advance mechanism. Found hose hooked up to Venturi vacuum. Correct hose attachment to manifold vacuum. Reset ignition timing to 22 degrees BTDC at 1700 RPM. Vehicle still idles poorly and hesitates at low speeds.
Perform cylinder balance by disconnecting spark plug wires while idling, Each cylinder drops while removing pertinent wire and spark click is heard. Remove all spark plugs and test compression while hot, 160 psi across the board. Rear spark plugs are blackish, Front spark plugs are whitish. Perform basic Weber down draft idle mixture adjustment to get poor results from both carbs. Smoke test each manifold. Apparent leaks from under front carb. Awaiting Weber carburetor kits at this time. Has anybody ever installed two individual intake manifold vacuum test pipes that would be blanked off when not in use? The cool whip tubs just don't seal well?

Thank you for listening.

Larry Louton
 
Hello Steve, I understand carburation but don't know the idiosyncrasies of a weber downdraft. How about I give it a go and if in need of bailing out then I will contact you.
This is the second time you offered me help, Seems like it's going to happen.
Thank you.

Larry Louton
 
I have the weber adapter that the sync meters fit in if needed. Did you check your secondary throttle plates for leakage? Just say the word, I’ll be on call :cool:
 
When I smoke tested the individual manifold and carburetor, I used a cool whip tub which did not seal 100%. But if done quickly and repeatedly I was able to find leaks in the base plate gaskets, possibly the throttle plate shaft’s.
Because of the cool whip tub seals the entire opening I just don’t know if the secondary plates are sealed at closing. The idle speed screw on the rear carb is is turned all the way in to the point of collapsing the tension spring.
Whereas the front idle speed screw has at least two turns to go. If you have that adapter, you must do this a lot. Carb kits are supposed to be here tomorrow.

Thank you

Larry
 

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I have the adapter for synching the throats, not the one that is the size of the cool whip container. You can make a suitable one of those by getting a rubber 6 inch (I think) pipe reducer which fits snugly over the bases then you'd close up the smaller hole (or make it fit the synchronmeter like i did back before my side drafts).

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Vacuum leaks at carb base will cause havoc, same with throttle shafts. Retard isn’t needed but vacuum is, but to make sure, you have vacuum hose attached ABOVE the throttle plate, correct? Your compression is good.
 
Hello Chris, I contacted the manufacturer of the 123ignition distributer in the Netherlands. My question was do I use manifold or venturi vacuum with this distributer.
The reply was manifold vacuum and to set the ignition timing with the hose disconnected and plugged to manufacturers spec.

Larry Louton
 
Larry Louton said:
Hello Chris, I contacted the manufacturer of the 123ignition distributer in the Netherlands. My question was do I use manifold or venturi vacuum with this distributer.
The reply was manifold vacuum and to set the ignition timing with the hose disconnected and plugged to manufacturers spec.

Larry Louton
Click to expand...
The vacuum above the throttle plate is referred to as 'ported' vacuum because the port is just above the throttle blade in its closed (idle) position. When the throttle is closed, this port is at atmospheric pressure. As the throttle opens, this port is exposed to the vacuum conditions in the intake manifold. Ported vacuum was used as a smog control measure.
The vacuum in the venturi is a result of the venturi effect and it is this vacuum that attracts the fuel into the carburetor. In vacuum secondary carburetors it is venturi vacuum that is used to power the secondary actuator.
Here's an excellent article on timing and vacuum advance.

 
You can use either ported or manifold vacuum on the 123. If using manifold you have to set it to kick in at say >2500 rpm so it doesn't affect your timing during idle and off idle acceleration. Ideally only kicking in at highway speeds. You also have to set the MAP curve so that when you do go hard on the accel pedal (passing on the highway for example) the vacuum advance curve drops out to zero. The only way to do this is to test drive it and set accordingly, otherwise you run the risk of too much advance under hard accel. The vacuum advance curve should be the last thing to worry about, disable it and plug the hose until you have your carbs running well overall. I can design a curve for you to get you started in due course.
 
Larry Louton said:
....should the vacuum line be hooked up to manifold vacuum or venturi vacuum?
Click to expand...
See Mike's explanation above.

As far as I can tell, there is no hook up on the stock Zenith or aftermarket Weber carbs for venturi vacuum. There are hook ups for manifold vacuum either directly into the intake manifold or at the carb above the throttle plates. As Mike indicates, the later is called ported vacuum but is exactly the same as manifold vacuum when the throttle plates start to open and uncover the port.

The choice is essentially to hook up the dizzy to the vacuum connection that gives the dizzy vacuum at idle (manifold) or not at idle (ported). With all other vacuum conditions produced by the engine, both will be doing exactly the same thing....that is advancing the timing at high vacuum conditions...primarily light throttle cruise.

I hook the dizzy advance at the manifold (stock dizzy). The engine is happiest at idle with the timing advanced. The idle speed increases as soon as you plug in that advance hose with no change in the throttle setting. Of course you have to time the engine with the hose to the manifold disconnected and plugged (you don't have to do this if you are using ported vacuum since the port is not uncovered at idle and no vacuum is going to the dizzy) and you have to reset the idle speed when you reconnect the hose after timing the dizzy.

If you are using a stock dizzy with two connections at the distributor vacuum canister, hook to the bottom (pyramid shaped side) of the canister. No connection on the other (top side) canister connection. Ported vacuum connections at the carbs should be plugged.
 
Larry Louton said:
Found first the question of removing the gas cap the tank would go woosh? Vacuum fitting on rear intake had been removed and brazed shut with a golf tee in hose. Hose fitting now has new pipe.
Click to expand...
I may be misreading this, but have you connected the hose from the charcoal canister under the battery that vents the fuel tank to the vacuum fitting on the rear intake manifold?
 
Dick Steinkamp said:
I may be misreading this, but have you connected the hose from the charcoal canister under the battery that vents the fuel tank to the vacuum fitting on the rear intake manifold?
Click to expand...
Right, the cannister gets hooked up to the air cleaner on one port and the blue gas tank line on the other. Both of which I have removed/plugged.
 
Dick Steinkamp said:
The choice is essentially to hook up the dizzy to the vacuum connection that gives the dizzy vacuum at idle (manifold) or not at idle (ported). With all other vacuum conditions produced by the engine, both will be doing exactly the same thing....that is advancing the timing at high vacuum conditions...primarily light throttle cruise.
Click to expand...
This is all done electronically with the 123 curve. So you can advance timing at idle with a custom curve and not rely on vacuum which can be inconsistent in these old cars. Much more simple to take idle vacuum out of the equation and just connect a source of vacuum for cruise advance and program the curve accordingly for when you want it to kick in safely.
 
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