Zenith carbs

[fredshealey]

Hello Guys
I do have a 1972 911 T which was converted to zenith carbs instead of the MFI.The motor is rebuilt with only 5k miles on it and here is my problem:
the car runs jerky at low rpms and also misfires at low rpms,but runs strong at high rpms.But if I run it at 5500 rpms in 3rd gear for a minute or so and then check the plugs they are white and theside elecrode looks burnt at the tip,which I think means it is running lean.So here is my question:
What size airjets and what size fueljets are supposed to be in there for it to work in the 2.4 engine.Hope someone can help since there is not much info about these carbs out there.
Regards
fred at fredshealey@aol.com

[al lkosmal]

2.4T engine set up;

Venturi = 30
Main jet = 130
Air jet = 180
Idle jet = 60

[James Brown]

When your running slow/low rpm, the carbs are on the idle "circuit" so the idle jets are in play when you accelerate the main jets takeover and there is a transition from idle to main jets. if the jets (main) are too small the a/f mixture can lean out and pop/backfire. Both circuits must be matched up correctly and the only wy to do that is with a a/f probe like an LM1.
Try opening the idle screws one full turn on each barrel and see what that does for low rpm drivability.




How's that Al fomr a new Zenith guy!!! BTW car is running great!

[5.8 Bandit]

Not to hijack but how about a proper setup for a cis 2.7 conversion with the same carbs.

[al lkosmal]

2.7 set up for CIS cams.
Venturi = 32
Main jet = 135
Air jet = 180
Idle jet = 55

2.7 with E or S cams
Venturi = 34
Main jet = 145
Air jet = 180
Idle jet = 60

PS: these numbers are right out of my carb notebook, but originally were provided by the PMO website. They should be considered good starting points. Then you need to tune, balance the airflow, air/fuel mix, float level, etc.........I.E. read up on the basic tuning procedures for the Zeniths. Search on Pelican for the Zenith manual. It is your friend. Use the following link to the Zenith manual..thanks to bill. http://www.billlevasseur.com/zenith

PSS: What James said . James...you have very recent, positive experience with Zeniths. Pass on the name of the venturi machinist for the 2.7 guy. (the only advantage that the Webers have, that I know of, is the access to various venturis and jet sizes....with Zeniths you need the Venturis machined if you need larger than 30's. ) James had some machined for his 3.0.

[5.8 Bandit]

Thanks for the info. And yes I would like the name off the machinist for the venturis.

[James Brown]

contact Jerrmy at pcar9119@yahoo.com for the size you need for the zenith carbs, great guy can make any size you want! and they work

[5.8 Bandit]

Thanks