Nick the knife

I’m having trouble finding the correct size main jets, Idle Jets and air correction jets to use with my motor setup. 2.4L 10.5:1 compression 2.7 Crank & rods 911T Cams.

Im using 34mm venturis and 140 main jets as recommend by Richard at PMO

Problem areas are

- Wont stay running below 1000 RPM
- Hesitation from idle to WOT
- (Feels a bit on the sluggish side compared to the 32mm venturi set up with the same main jet)




If any of you guys have a 2.4 911S with Weber 40IDA’s or have setup suggestions to offer I’d much appreciate it, as I am pulling my hair out trying to get these things to work properly.

A Quiet Boom

Sounds like two problems there, have your gone through the sychronizing and idle adjustment process? Also make sure your accelerator pumps are properly adjusted. Once you've done that if it still hesitates try bumping up to a 1.45 or 1.50 main jet. Stay away from the air jets for now they are mainly for fine tuning and best left alone by a carb novice. Also 34mm venturis is a bit large for a 2.4 engine with a relatively mild cam like the T. To often people use more carburator than they need with poor results and sometimes less HP than a properly sized carb. I run 36mm venturi Zeniths with 1.50 main jets on my 3.0SC engine. Based on the following equation 32mm would be closer to the correct size.

Choke in mm = [square root of] (Cylinder Volume X RPM)/2600

Inputing 400cc's per cylinder and a 6500rpm power peak I get 31.62mm for your engine.