Another "my 950 is too rich" thread. I've posted on RFS but not gotten much response there.

Anyhow, I recently bought one for my 451 (from a carb guy who used to be on here, and we are talking on RFS) but I'm considering sending it back and I eat $50 plus shipping. (1.45" venturi, Holley ultra baseplate, and I think a Proform body, billet metering blocks, Ultra fuel bowls with sight glass).

It seems to be untuneable for efficient street use with my combo (451, 272@.050 mushroom cam)- just too rich at cruise and part throttle, which is where a street driven car spends most of its time. Too bad, because it feels great for driveability and really hauls ass when I hit the secondaries that I haven't even tuned yet.

The problem (many threads I've found by Googling, including on here) is that it's big enough that I have to run on the t-slots, even at 60 mph, 3000 rpm. And the 15" cruise vacuum sucks harder on the slot than the 8" idle vacuum... 13.8-14.0 at idle with screws out about 1-1/4 turns. 5.5 PV, 77/86 jets.

With the 950, I can see richer than 11:1 at the very top of the t-slot at low load and below 2000 rpm where the mains start to come in! Which is exactly the point where I'm putting around at 30 mph.

I went back and read my earlier posts on RFS about my 4780-2 that I converted to replaceable brass and a 4-corner idle with QF 12-700 baseplate. Although the same problem exists (12:1 at top of t-slot), it cruises at 14:1 or better and that is ok). I can't get this carb to do better than 12.5 low speed and (maybe) 13 at 3000 rpm.

I've gone all the way down to .045 primary TSR, and .031 IFR, .082 PIAB. And it STILL runs 11.5-12:1 at the top of the t-slots below 1800 rpm, but 16:1 lean at tip-in (no flat spot yet but I probably can't go much leaner before I can feel it). Last ditch will be to take the IFR down even a little more, maybe .029 or .030.

My 4-corner (and replaceable brass) conversion on the old 800 4780-2 works better than this - I tweaked some more and can cruise at 15.5:1... although there is a slight flat spot at tip-in I can live with.

So - I think I'm trying to do the impossible with a big cam (decent street manners and fuel mileage when my foot's not in it, and lots of top end horsepower).
I want a big 4150 carb but don't want to cruise on the t-slots.

Is there some way to make the t-slots smaller (or even tapered) that won't break the bank? I don't have the talent to try that.
Thanks for any help.