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]

how low of an egine speed are we talking about when the carbs are "full open" and it bogs? like REAL low, you nail the gas and the car goes on it's nose til the engine catches up?

k

[bjinright]

how low of an egine speed are we talking about when the carbs are "full open" and it bogs? like REAL low, you nail the gas and the car goes on it's nose til the engine catches up?

k

About 1500rpm. but it happens at 2000 and 2500 if I hit the gas. I'm not talking about slamming it from idle, just a full depression of the gas at low rpms. I get a little power back when I let off the pedal a bit and it wont bog under a slow progressive depression of the gas.

I had an off idle stumble back when I had 34vents. I think this is different.

It started 1 month ago and happened right after two events.
1. Went autocrossing and over revved the engine 7000 rpm a few times ( i was winning at the time)
2. put the tall idle stacks on when I got back that day (thought it was a clog and so made the change when I checked all the jets, and yes I used the little plugs)

So It could be that:
1. the timing was thrown off
2. the cam gear moved (unlikely)
3. the valve clearances are off or worse
4. the tall stacks blow more air (i know thats wierd)

I checked the timing . . . fine 30btdc @3500
The valves and cam gear are being looked at now. I think a have a stock cam by the way.
And I'm checking the dells for leaks.

Before it was fine with 55idles and 35pumps. But after sunday, pop cough bog. So I started going richer 60 idles then 50 pumps.

In week or two it will be back from the garage and I will have something to work with. A/F ratio meter, and valve adjust.