Mallory Dizzy setup

[richiep]

Just bought a mallory Unilite optical with Vacuum advance for my type 1 - 2110cc, FK10 cam, twin webber 44 IDFs

Anyhoo, was wandering if anybody could explain to me how to go about setting the thing up

Mainly how the vacuum is set up to work. Some people have told me the VAC is used to retard the ignition when cruising i.e. middleing revs but fairly low throttle.

Some say in these conditions the VAC will advance the throttle.

I've read aircooled.net's description of how it works, and that confuses me more.



Can any body help?

Oh yeah - dunno if its relavant or not but the car is gonna be used for circuit racing, not drag racing and I wouldn't mind a few more MPGs and longer engine life (cooler running) if this is possibe?


Cheers

[Shad Laws]

Hello-

Anyhoo, was wandering if anybody could explain to me how to go about setting the thing up

You can basically consider the centrifugal and vacuum portions totally independent for tuning purposes.

Take care of centrifugal stuff first. Put in the springs you want and setup the distributor centrifugal advance at what you want (example: if you want 28º max and 10º idle, then you need 18º of distributor advance). This stuff is well-documented by Mallory.

Install the distributor in the car, and with the vacuum line disconnected, go ahead and set the timing like you would a 009. Make sure the centrifugal part works as you expected.

Now, after that's done, you can take care of the vacuum. At least on the units I've gotten, this stuff is very poorly-documented by Mallory! The point of the vacuum canister is to advance timing more at low-mid load, i.e. it advances more with more vacuum. At high load, the vacuum goes away, and the vacuum advance goes away - it becomes just like a regular 'ol centrifugal advance distributor at WOT.

You want to read the vacuum just barely above the throttle plate, ~90º away from the shafts, on the side such that the throttle plate will pass over it when you open it up. If you understand carburetor design, then you'll probably identify this location as more-or-less the same spot as the progression circuit ports. This makes sense - the progression ports see vacuum except when at idle or very high throttle, which is the same thing we want for the vacuum advance. New Webers have ports already in there for you - one per carb on the outboard sides (they have a screw in them to block them off out-of-the-box). Otherwise, you'll have to put in ports yourself.

The Mallory vacuum canister isn't all that adjustable. It allows you to adjust the total amount of maximum advance by sticking an allen key in the canister opening and turning, but it doesn't allow you to alter the amount of _vacuum_ needed to get it to move. As a consequence, you really need to set up a vacuum port on at least two of your carb throats.

You can see how much advance it gives you like this: put a long tube on the canister and start up the engine. Have someone hold it at some rpm above the point where the max centrifugal advance happens and put a timing light on it. Then, using your mouth or a hand pump, apply a vacuum to the canister and see how far it will advance, i.e. how many extra degrees of timing you got. I'd set it to about 8-10º.

After this, attach the vacuum ports of the carb throats to a tee and run the line to the canister. You should be done!

Oh yeah - dunno if its relavant or not but the car is gonna be used for circuit racing, not drag racing and I wouldn't mind a few more MPGs and longer engine life (cooler running) if this is possibe?

That's exactly what the vacuum advance is good for - more mpg and cooler running head temps (unless you always drive at WOT :-).

Take care,

[richiep]

Thanks for the reply Shad, very informative and a million times clearer than what anyone else hase told me!

The place I bought the dizzy from (an aircooled.net supplier to the UK) told me the vacuum retarded the advance!

I'm not entirely sure what aircooled.net's description of how to set this thing up was telling me but I understood it to be that basically it gave you an extra 10 degrees or so max advance when cruising.

Both of these seemed 'wrong' to me.

It may be that I have missunderstood what the suppliers of these parts have been telling me or it may be that they just plain got it wrong.

At the end of the day I suppose that Mallory should provide a clear description of how the Unit works along with at least some idea of how to set it up.

Thanks again for your time.

Rich