What carbs were installed on the 911 R, ST, RS, & RSR

klober23 · klober23's Garage

I'm just curious on what carbs were installed on the 911 R, ST, RS, & RSR? Can anyone give me a break down?

Thanks

jbell959 · 01-08-2015, 08:05 PM

The ST, RS and RSR all ran Mechanical Fuel Injection. Just the R would have run carbs and it would have been 46IDAs I believe.

klober23 · klober23's Garage

Is there a difference between the weber 46's issued to the R?

jbell959 · 01-08-2015, 08:41 PM

I'm not an expert, but I don't believe there is any difference between 46's other than the jetting. The R had special tall magnesium manifolds which are hard to find and very expensive if you do. I've seen aluminum repros that are much more affordable.

klober23 · klober23's Garage

Thanks for the info, you are the man. Greatly appreciated.

BURN-BROS · 01-09-2015, 07:44 AM

List of Competition engines that ran the 46's

901/20...906
901/21....911R
901/25....914/6GT
901/30....2.0 liter rally
911/22....85x66 ST? engine for 71

The throttle arms were different for the 906.

KTL · 01-09-2015, 09:04 AM

The Weber 46 in the racing application also used the tall secondary venturis. You know the ones, they're the ones that start to wobble over time and loosen up the slots in the carb throats, resulting in a loss of fuel draw & loss of power!

chris_seven · 01-09-2015, 10:30 AM

I believe that the 911ST with the 2.3 motor ran an MFI system and developed about 240BHP

There was a 2.4 developed in 1970 for the Tour De France used 46IDAs giving around 250BHP and the 2.5 litre cars ran 46IDAs and developed 270BHP. Some of the 2.5 litre cars ran an MFI but most used carbs.

Steve@Rennsport · 01-09-2015, 05:45 PM

Quote:

Originally Posted by KTL

The Weber 46 in the racing application also used the tall secondary venturis. You know the ones, they're the ones that start to wobble over time and loosen up the slots in the carb throats, resulting in a loss of fuel draw & loss of power!

Actually,........they don't loosen all by themselves (I've had & used them in a LOT of engines since 1967). They need human beings to make this happen.

Seriously though, like many things, its "human factors" that make problems where there weren't any.

klober23 · klober23's Garage

Steve, you have my interest now, what mistakes or incorrect installation makes these loosen up?

KTL · 01-12-2015, 06:45 AM

Be that as it may, the tall venturis are definitely more prone to being loose than the short ones. I suspect it's because the tall venturis provide more leverage for someone to remove them. Instead of people pulling straight up on them to remove, they use the long neck on the venturi to "rock" it out of the slots and that loosens the fit.

A loose fit is problematic because it doesn't provide a tight seal for the fuel to be pulled via the airflow/venturi effect. I've experienced the direct effect of tightening the fit of these venturis. At lower rpms, the improvement in power is shocking.

A good way to tighten the fit is:

1. Make sure the fuel side of the venturi is nice & flat by lightly surfacing the fuel "leg" of the casting on some fine grit sandpaper (with a flat surface!)
2. Bend the spring in the venturi to increase the spring pressure holding the venturi into the slot. However, the spring tends to relax over time.
3. Choose an appropriate thickness of feeler gauge to use as a shim. Cut to size and push/tap in place on the spring side of the venturi.
4. Enjoy significantly more power from your carbs!