Jet sizes for Webers on a T

[retrotech]

What would be suggested for Webers on a 2.4T with E cams?
Emulsion tube
AC jet
Idle jet
Main jet

All advise appreciated.

[GotaT]

Main 180
Idle 60
Emulsion f28
... If my memory is correct.

[Peter Zimmermann]

Originally Posted by retrotech

What would be suggested for Webers on a 2.4T with E cams?
Emulsion tube
AC jet
Idle jet
Main jet

All advise appreciated.

Obviously, because every "custom" engine is different (compression, cam timing, port sizes, etc.), the following specs should only be used as a starting point. Use Bosch WR6DC (W6DC) plugs gapped to .030" and read your plugs before any aggressive driving.
Emulsion tube: F 26
Air Correction: 180
Idle fuel: 55 (maybe 52)
Main Jet: 125
Venturi: 30

[jkh2cpu]

I got my Webers in 1987 for my 1973 911T MFI, and the Air Correction jets were 170, the mains 1.30, and the idles 55-60. When did these 'new' vaules surface? Or, put another way, how late to the party am I Seeing as how the transition is flat and a bit rough, I'm guessing that larger AC jets would be a good idea.

I got an LM-1 last week, and even with 55 idles and 1.25 mains, the car is still a little too rich for my taste. If I drop the idles down to 50, the car is too lean on the idle circuit. Any recommendations on what sort of business can ream the 50s to 52 or 53?

TIA.

John.

[Peter Zimmermann]

Originally Posted by jkh2cpu

I got my Webers in 1987 for my 1973 911T MFI, and the Air Correction jets were 170, the mains 1.30, and the idles 55-60. When did these 'new' vaules surface? Or, put another way, how late to the party am I Seeing as how the transition is flat and a bit rough, I'm guessing that larger AC jets would be a good idea.

Oh, those aren't "new" values, they come out of my note vault that covers many years of trying to optimize Weber set-ups for different cars. Your car is unique in that you have cams that are considered mild, a relatively low compression ratio of 8.0:1 (possibly only 7.5:1), and 32mm ports; not the best way to make carbs work well (the 2.4 T MFI cars gave us the biggest headaches!). You fail to mention your venturi size or emulsion tube number, both are very important to know when trying to improve overall running. Also, if you know it, what is the I.D. of the intake manifold where it meets the intake port (you want to do whatever is necessary to avoid having a "step" at that mating point)?

[jkh2cpu]

The 'Chokes' are 30 mm, and the emulsion tubes are F26. The manifolds that came with the kit from PMO were 40/32. The compression ratio on the 1973 2.4 T is 7.5:1

Any idea on where I can get the 50 idle jets reamed out to 52-53, and will I see a significant change in transition if I go from 170 to 180 for the air correction jets?

John.

[Peter Zimmermann]

Originally Posted by jkh2cpu

The 'Chokes' are 30 mm, and the emulsion tubes are F26. The manifolds that came with the kit from PMO were 40/32. The compression ratio on the 1973 2.4 T is 7.5:1

Any idea on where I can get the 50 idle jets reamed out to 52-53, and will I see a significant change in transition if I go from 170 to 180 for the air correction jets?

John.

Give PMO a call, Richard can shoot you out a set of 52s, and ask him to send you a set of 180s at the same time. The transition on 2.4 Ts is the roughest one to try to smooth out, your venturis are OK, but you might check with Richard on the tubes - you just might have better success with F2s, maybe even F1s. Due to the small ports, you might also want to ask him if he's reconsidered the venturi size, and if 27s might be worth a try.

[Jim_Brown]

Pete and John-

PMO updated their recommended jetting for small stock motors in their March '08 advertisement in Panorama. They now recommend 30mm venturis, 130 mains, 50 idle and 180 air correction. They'll exchange jets for customers wishing to update.

Cheers,
Jim

[retrotech]

what emulsion tubes??

[Jim_Brown]

They didn't inculde an emulsion tube recommendation.

[jkh2cpu]

Peter: Thanks for the PMO recommendation; I just sent a fax.

Retrotech: you are running E cams in a 2.4 with T pistons? How does that work? I assume that you set the cam timing for the E cam, right? No piston / valve collision?

Jim: I saw the PMO recommendations, but figured that they were for the PMO carbs, not the Weber carbs.

John.

[retrotech]

I have no information other than previous owner said it had E cams, all else is stock.

[jkh2cpu]

Retrotech: the PMO information that I have from 1987 gave these specs:

911T 2.4

Chokes (Venturi) 30
Main 130
Air Correction 170
Idle 55-60
Emulsion Tubes F26

****

911E 2.4

Chokes 32
Main 135
Air Correction 180
Idle 55
Emulsion Tubes F26

Heh! I'd fax Richard at PMO (310 394 6313) and get his opinion. I'd guess that you would set the carbs up according to the cams, but seeing as how you have lower compression ratio pistons, I don't have a clue. Old cars have lots of excitement, even when standing still ;-)

John.

[jkh2cpu]

Here's the closure on this one... I did contact Richard at PMO, and he suggested .55 idles and 1.25 mains. The car was still running rough on this combination, but the AFR was around 14.0 in cruising, and at safe levels (13.5) at WOT.

The problem was the ignition and specifically the points. I installed a new pair set the gap and got the dwell close to the ball park... There was much improvement with this, but the car was still acting odd: the tach would occasionally idle fast than the engine was running, or indicate 2000 rpm when the engine was turning over at 1000-1200 rpm. If I had been breezing down the interstate at an indicated 80 (really just 75 according to my stopwatch and mileage markers), the tach and engine would drop down to 600 rpm and then slowly recover to the expected 1000 or so; even so occasionally the tach would show the false value of 2000 rpm. Besides all of that, the strobe showed that the ignition at idle was firing at 7 BTDC, with a plus-minus of 2 or 3 degrees.

I got a pertronix for the car... The car is a T that came with MFI, and the distributor was 0-231-169-008, which is not listed by our host. I checked the factor manual (bought it in 1974 for 80 bucks: four volumes), and it said that the 1972-1973 distributors were the same except for the rev limiter, so I got the PEL-PT 1863. It installed like a charm, except that the 6-32 nuts looked and acted like 4-40; I got 6-32s at the hardware for 7 cents each. It fired up and ticked over like it was brand new. Better yet, the tach was rock solid at idle, and the indicated tach rpm was the engine rpm. Coming off the expressway, the idle dropped like a rock to 1000 and stayed there like a rock. The stobe now shows idle at 7 BTDC with nearly undetectable variation.

I'm a happy camper. Now I have to reconstruct the 2.7 short block that I bough several years ago and shoehorn it into the car. If it gets decent mileage, I'll keep the webers, otherwise I'll look at some aftermarket EFI setups.

John.