Dual carb question, Dellorto 40s on a 1.8L to be exact Options

[terrymason]

The problem - The car will go very lean around 2500 rpm, as if the pump jets were too small.

History:
New fuel pump (3.5 PSI to each carb)
55 idle jets
55 pump jets
140 main jets
175 air correctors
These carbs are new to the car, and I'm trying to dial them in.

The car is lean when I first start it (16 / 17 on my air / fuel gauge), but then levels out to a nice 14.7 idle when warmed up. While driving, I can give the car 20% or so of the pedal, and drive up to highway speeds nicely, but when I goose it, it will go very lean (18-22 on my gauge) followed by a series of backfires and loss of power. I started off with 35 pump jets, and have moved up to 55s, which appear to be the most popular around here. I've also adjusted the pump jet linkage, from the nut fully loosened, and moved it in as far as it would go before affecting the main throttle shaft (like 60 turns or something).

What do you guys think, do I need 75 pump jets?

[Twystd1]

If you choose to use a factory vacuum advance 914 Bosch dizzy on carbed engines.

NOTE: You can run a pertronix or Crane electronic setup in any of these dizzys. And thats a good thing IMnonHO.

You have a couple of choices.

!) Get your ported vacuum above the throttle plates. On some carbs there is already a vacuum port for this. On some there isn't. In that case you have to drill the carb body and install one. It's pretty dam easy to do. Then you epoxy a brass fitting in and VOILA.. Insta vacuum port.

At that point you will need to have BOTH carbs ported to vacuum. ONE carb doesn't work well.
Why you might ask...?????
Because of venturi fluctuations of the valves closing and opening. That will pulse the dizzy vacuum diaphragm and create all kinds of timing fluctuations. And thats bad....... Ya can't tune around it.

So what ya do... is is get 2 matching ID sized rubber hoses to each vacuum port on each carb. Then each hose to a Plastic or Brass "T". (Combined signal of both carbs)
Now comes the fun part. Go to your nearest parts house or even better.. A Vee Dub shop. And get one of those little plastic fuel filters that you have seen on every old Vee Dub engine you ever looked at. They are like a buck or two. Put that filter inline with the last hose that comes from the "T" to the Dizzy vacuum pot.

This will help dampen out the vacuum pulses that occur at lower RPMs and keep the points palte via the vacuum pot from over reacting to the pulses.

DONE....!!!!!

2) Don't run vacuum advance on your stock type IV distributor..
And leave the dizzy port OPEN. Else the vacuum pot will create resistance on the points plate and prevent it from clocking (turning) at the proper rate according to engine rpm.

3) Buy a Mallory "Non Vacuum Advance" electronic dizzy. Thats the best of the dizzys. No vacuum pot... No problems.

4) Buy a SVDA dizzy for a type IV engine from John Connely at www.aircooled.net
That is a very good vacuum dizzy that is curved for a type IV engine.
Note you must have vacuum fittings for this carb.

Lastly. Vacuum advance helps on fuel mileage and constant RPMs efficiency. Like a freeway or any long steady state speed driving.

If'n this engine is for having fun and hauling ass on turns. Auto X or simply occasional driving. I don't think the advance setup is worth the trouble in your case.

Anyway... thats what I think.

Now go make it work......!!!!!!!!

And I am glad you are tossing that piece of crap 009 dizzy. Those little critters have screwed up more Carbed type IV engines that anything I know. Period.

Cheers,
Clayton