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?

[eric914]

Not to hijack but I have 40 IDF's with an 009 dist. If I put the factory dist back on where do I port the vacuum from. Can I use one of the ports at the base of the carb? Do I need to connect the ports from both carbs together to keep the flow through them the same? I am also having some backfire issues and the motor seems flat when accelerated hard in the 3500+rpm range.

[BxtrBill]

[quote][quote name='eric914' date='Aug 2 2007, 02:01 PM' post='930974']
Not to hijack but I have 40 IDF's with an 009 dist. If I put the factory dist back on where do I port the vacuum from. Can I use one of the ports at the base of the carb? Do I need to connect the ports from both carbs together to keep the flow through them the same? I am also having some backfire issues and the motor seems flat when accelerated hard in the 3500+rpm range.
[/quote]

Well, seein' as how the hijacking has already been done (and also seein' as how other folks might want to know), vacuum for the distributor advance is always taken from a point ABOVE the throttle plates. If you have the later version of 40IDFs (hecho en Espana, I believe?), they will have one port on each carburetor that you can use for this, Seems to me the earlier (Italian) versions have none, but I could be wrong....been a while. In any event, do not use any port that is below the level of the throttle plates unless you need to feed a vacuum retard can.

You can parallel the vac ports on the two carbs and I do, when I have two to use.
Lots of Dellorto pairs have only one vac port on one carb and I'll be danged if I can tell the difference.

I've used the stock 1.8 dizzy and I think it's a good choice for a carbed car. That said, I like the -205 distributors from early Jettas/Rabbits/whatnot, though they do require a bit of lathe time to make them work. A distributor from a later Bus will work too, and slips right into the hole in the case. The neat thing about these options is the bulletproof FACTORY electronic ignition that comes as part of the package. I fiddle with the advance curve some, set the timing and pretty much never look at them again. If you go this route, be sure to get the so-called Fairchild module, the special coil and the wiring harness to connect everything together.