Distributor Vacuum Question

Grant-

Ported vacuum is load dependent. With the car stationary, you might not be able to generate enough vacuum (load) to pull the can on the distributor.

If you by a "Mity-Vac" vacuum pump, you can see exactly how much vacuum it takes to pull the advance on the distributor. If you hook a vacuum gauge to the ported vacuum on the car, you can see how much vacuum you are generating at various load conditions.

If the vacuum the car is making exceeds the vacuum it takes to pull the advance can, it's working.

Hello Stan and thanks for your input.

I drove around today with a vacuum gauge run into the passenger compartment and connected with on and then the other carb vacuum port to check what the vacuum signal was under different driving conditions.  The result is the Kadrons only pull between a 2 to maybe a 6 inHg signal.

I then teed off a vacuum line running to my distributer vacuum canister to the gauge with me as the vacuum source and measured that it took about an 8 inHg vacuum to get the actuator moving.  The is consistant with info from Pertronix saying that a minimum vacuum signal of 8 inHg is needed for its vacuum mechnism to perform.

Now it seems that the issue that I have is that I have carbs that while providing a proper ported vacuum signal just dont put out enough of a signal to take advantage of the vacuum advance feature of my distributor.

This is a pisser because before deciding to run the Kadrons my 34PICT3 carb (running on a single intake manifold) was able to generate a strong ported vacuum signal of 8 to 10 inHg so that my distributor was able to give the desired total advance of around 40 degrees BTDC.  This makes sense if you think about (my vacuum signal at each Kadron being about 1/2 of what is was with the 34PICT3 carb by virtue of splitting the single intake manifold system into 2).

Any thoughts and/or observations would be greatly welcomed.

Thanks, Grant

Grant- Where did you buy the distributor?

Grant-

My Bosch SVDA distributor takes about 4.5" to begin to pull the canister. I've got a vacuum advance Mallory Uni-Lite with an adjustable vacuum can-- it can be adjusted down to pull with barely any vacuum. I've heard that the Mallory can can be adapted to a Bosch (or Bosch-like) distributor (John Connelly from aircooled.net said this).

This is one option to your problem. There may be others, but I can't think of any.

I bought my distributor from So Cal Imports in Long Beach.  Its a Pertronix SVDA Flamethrower with an eleectronic module.  Again, it worked great with my 34PICT3 carb, but that carb had a vaccum signal of up to 15 inHg.

I am going to try calling Pertronix on Monday to see if they offer any different more sensitive vacuum canistors.

I have also read on some VW blogs that some have opened up (drilled slightly larger) the very small hole in the carb at the base of the vacuum port.  I recall when installing the brass tube in the vacuum port that is had a very small opening at the base.  This could possibly account for the weak vacuum signal.

I have also read that AJ at Lowbugget sells an SVDA that is curved and treated to work with the Kadrons.  I may try calling him on Monday as well to better understand what he does to his distributors to make them work, and if they are able to provide a total advance of 40 degrees with vacuum.

All good input and very apprecated.

Thanks, Grant

Before you start throwing money at Low Bugget, look up the company and AJ in the Samba's feedback forum; his service when dealing with out of town customers seems real hit and miss. John from aircooled.net and Jeff at Kaddie Shack also set up svda's for dual carbs and may be able to help.

I agree with Al; give contact Jeff:  http://www.shop.kaddieshack.com/main.sc