2.4E Zenith jetting suggestions please

[jim72911t]

Hi all,
I have a 1972 911T with a freshly rebuilt 2.4E spec motor, using 2.2E pistons, as per Wayne's book. In order to defer the $2500 or so it will take to rebuild the MFI properly (yes, it will go back on the car, relax ), I picked up a set of Zenith carbs cheap, and have since rebuilt and installed them. Good news: the car runs okay now, which it not do with the worn out MFI. Bad news: it doesn't run great, probably because I made no jetting changes before I put them on the car. (I was in the "put them on and see what happens mode")

Anyway, I'm running the following jetting:
Venturies: 30mm (I bored them out when I had the carbs apart)
Main Jets: 115
Idle Jets: 47.5
Air Correction: 195
Emulsion tubes: 30 (?)

Anybody have a baseline for my particular engine? I've done some pretty extensive searches on this board and others, and I found lots of info on Webers, but little on the Zeniths. I'm assuming my carbs are still set up for a 2.2T.

Oh yeah, my car has one of those Bursch 3-muffler "made for MFI" exhausts, which is not only obnoxiously loud, but makes me wonder if it will ever be suited for the carbs.

Thanks in advance,
Jim

MFIWDP, please be easy on me

[Grady Clay]

Jim,

One of the difficulties with Zeniths is the lack of availability of tuning parts compared to Weber/PMO. Yes, you can take small jets and drill them out, large jets and silver-solder them and drill smaller, and make new venturi. All doable but a PITA compared to having a box full of Weber jets and parts.

Any carb is more forgiving compared to MFI when choosing mufflers. This is because all carbs have feedback and MFI doesn’t.

I know of several 911s that have Zeniths as EFI throttle bodies.

Best,
Grady

[jim72911t]

Grady,
Thanks for the quick reply. You've alluded to my dilemma and possible solution: ream the jets. Since all the research I've done indicates that I am most likely lean, I'm looking more for a starting point with regards to jetting.

Or, more to the point: will Weber numbers correspond or get get me close?

-Jim

[austin552]

Yes it seems Zenith 40's are a match with the 2.2l. Still linking mine along with several other tasks.

[jim72911t]

Any more thoughts?

Thanks