Vacuum retard distributor??

[Vixenpilot]

Hello!

I'm working on a 73 MGB, smog equipment removed. The manual states that during dynamic timing, retard has the marks moving clockwise and advance has them moving counter clockwise. I assume this is as viewed while standing in front of the car, facing the car. If this is the case, does this car incorrectly have a vacuum retard distributor in it? Not sure of the origins of the distributor but it IS a 25D. Is there such an animal? With the advance unhooked and the manifold plugged I can set the timing. When the engine is revved, the mechanical advance slightly retards the timing and takes power from the engine under acceleration. If I plug in the vacuum advance There is no power at all under acceleration. At this point I run the car with no vacuum advance with the timing set so advanced that the carbs no longer have idle adjustment. Seems to me the car needs a proper advance distributor. Does this sound correct and once again, is there such a thing as a vacuun retard 25D distributor????

Thanks for any input!!!!!

 

[SilentUnicorn]

yes - I believe there is such a thing as a vacuum retard dizzy. The first question i would ask is: Where are you getting your source vacuum? Ported or manifold?

generally, when talking about dizzy rotation you should be looking straight down at the dizzy from the top.

If it is ported vacuum there should be no vac adv at idle. If manifold vacuum you should see vacuum on the line at idle.

Make sense?


m

 

[Vixenpilot]

Thanks!

The vacuum is coming from the intake manifold. The question I have is this car should have vacuum advance, not retard..right? And could it have the wrong distributor?

Thanks again!!

 

[SilentUnicorn]

It will run better with a vac advance distributor. Is it the right dizzy? My book shows 25d and 45d. and i have not found any mention of vac retard. Pretty sure you could use either. What ignition are you using? and what carb?

What happens if: you unplug the advance and plug the hose- then get the timing set and the idle nice and low Then plug in the vac advance line? the idle speed should increase noticeably requiring you to decreases the idle speed. This would show that the advance is happening as it should.

The other way to check is to use a vacuum pump and see which way the plate in the dizzy moves when you apply a vacuum to the dizzy. it should move CW if it is advancing.

m

 

[JPSmit]

Not sure about the 'B's but I know my Midget (1500) has a Vacuum Retard distributor - was part of the anti-smog stuff of the day. At the Midget 50th last year Jeff Schlemmer told me to disconnect it and the car would run better and cooler. You might want to contact Jeff (Advance Distributers) not much about them he doesn't know and he is great to help!

 

[DrEntropy]

A hearty here.

Vacuum pots on a 25D would ordinarily be ONLY advance, but ISTR a pot with two vacuum pipes, one advance, one retard.

I've a 25D on both remaining Lotus cars with NO vacuum pots. The variants are, ummm, various.

 

[Vixenpilot]

Thanks for your input everybody! The fact that it runs better with the vacuum disconnected says a lot I think. This WAS a smog car.

Unicorn, Using, Pertronlx ign. and HIF carbs freshly and completely rebuilt. After setting the timing and reapplying the vac, the rpm drop. I'm going to see if I can dig up another distributor for comparison.

Thanks again!!

 

[SilentUnicorn]

Thanks for your input everybody! The fact that it runs better with the vacuum disconnected says a lot I think. This WAS a smog car.

Unicorn, Using, Pertronlx ign. and HIF carbs freshly and completely rebuilt. After setting the timing and reapplying the vac, the rpm drop. I'm going to see if I can dig up another distributor for comparison.

Thanks again!!

that certainly sounds like a retarded dizzy....

some reading:

https://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf


m

 

[Vixenpilot]

Great read! Thanks!! I'll fill you guys in on the results

 

[Billm]

I am fairly certain that any of the advance/retard mechanisms can fit any 25D or 45D distributor.
It would be very easy to remove your "pot" and put the correct one on but FAR better would be to get one from Jeff (Advanced Distributors) and have him set the centrifugal AND vacuum for you engine as it is now!
BillM