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?

[rhodyguy]

ok. linkage off. flow set the same side to side with the idle adj screws. now attach the rods with one of them longer than the other and touch nothing else. check the flow rate now!! a c-note says it's off. flow is flow. with the throttle plate opening the same at idle it will be, or should be, the same throughout range of operation

on a side note, not all webers are 'built' the same. some have 'helper' springs on the outside of the throttle plate bars and some don't. w/o the helper springs, linkage disconnected (this means no cable return spring), start the car. bottom line, do what works best for you. my method works swell for me. my carbs don't snap or pop, nor does my car backfire on decel.

k

[type11969]

Well, if one rod is longer than the other and it forces the throttle plate open on one side, then the linkage IS NOT adjusted properly, now is it? It is interfering with the initial settings and should not be. Obviously the flow will be different because one plate is open more than the other (thanks for the really tempting wager though). It would be at this point that I adjust the linkage such that the idle screws are resting on their stops (matching the initial sync), then I would verify that the butterflies both open fully and at the same rate.

What I am doing is setting my linkage about my initial position. What you are doing is setting your initial position about your linkage. Which one takes more fiddlin I don't know.

Snapping, popping, or backfiring usually is not a sign of a poorly set up linkage, but I am glad your car doesn't suffer from any of those maladies.

-Chris

ok. linkage off. flow set the same side to side with the idle adj screws. now attach the rods with one of them longer than the other and touch nothing else. check the flow rate now!! a c-note says it's off. flow is flow. with the throttle plate opening the same at idle it will be, or should be, the same throughout range of operation

on a side note, not all webers are 'built' the same. some have 'helper' springs on the outside of the throttle plate bars and some don't. w/o the helper springs, linkage disconnected (this means no cable return spring), start the car. bottom line, do what works best for you. my method works swell for me. my carbs don't snap or pop, nor does my car backfire on decel.

k