Weber question

[obrut]

I have webers on my 2.7 litre RS replica race car.
The car has been dyno'd at 190 flywheel hp and has a huge flat spot and power dip between 3000 and 4000 rpm (a/f drops to nearly 10:1). You can drive through this patch at part throttle but it really bogs down (ie. you nearly headbutt the steering wheel) if you use full throttle at these revs.

Carb specs are: main jets 135, idle 55, acc 55 & emulsion 140.

My mech suggests changing the venturi tubes to long style (906 style?). Anyone know where I can get these?

Where should I start to solve this problem? All suggestions appreciated.

[Fishcop]

I was suffering a similar problem with my 2.2 a few weeks ago, but lower in the rev range. Turned out to be a stuffed accelerator diaphram on the left bank. Replaced it and "perfect". Sorry, I'm no guru though.....

I rebuilt my webers a while ago, very easy job. You may want to consider running a kit through them if you are going to go to the trouble of stripping them down to replace the secondary venturies (they are the little tubes in the middle of your main stacks that your machanic is recommending).

Stan Adler at "Performance 911" in Melbourne carries a lot of this stuff 03 9318 7515.

Cheers

[T Bird]

obrut
The problem you describe, a flat spot above 3000 RPM, is generally occassioned by the wrong emulsion tubes. The tubes are probably causing a rich stumble due to an under-emulsified mixture between 3000-4000 RPM. This supposition is supported by your a/f ratio, which indicates a very rich condition in this RPM range.

I believe that Bruce Anderson's book makes specific recommendations for emulsion tubes and jetting for an engine such as yours. Unfortunately, my copy is at home and inaccessible to me at the moment.

The first thing I would do if I were you is to verify ALL jet sizes and the particular emulsion tubes you are employing. Then compare this information to the data found in Anderson's book, or to the collective wisdom of board members with set-ups similar to yours. After you determine what jets and tubes put you in the ball park, you need to tune these Webers. I posted step-by-step Weber set-up proceedures a while back. I can e-mail you a copy if you can't locate them via the Search function.

BTW-it would be good to know your engine specs-- is the engine a 2.7 RS? Also, am I correct in presuming that the engine runs well above 4000 RPM?

[obrut]

John

I have Bruce A's book as well and will check the specs he recommends. In answer to your qns, the car runs great above 4000rpm and is essientially 2.7RS spec but with webers not MFI. I also suspect at least one of my throtle shafts is worn and allowing a little air ingress. They are coming off and apart tonight.

BTW, I'm in Australia, where in the US would you think is the best place to buy weber bits (someone with a website would be easiest)?

[porsche74]

Obrut:

I'd suggest that you remove the air corrector jets and see which emulsion tubes you have.

These are matched to the camshafts and you should have F3's.

FWIW, I use a round wooden toothpick to remove the m as it will not damage the soft brass.

[T Bird]

obrut
The best place in the US for Weber 40 IDA 3C parts, tools and advice is PMO, 135-17th St., Santa Monica, CA 90402. The proprietor, Richard Parr, knows more about Webers in 911s than possibly anyone else in the universe. PMO's phone # is (310) 393-5423. I don't have the fax # handy, but can supply later today if someone else doesn't chime in.

The fact that your car runs well above 4000 rpm further supports my belief that the emulsion tubes are probably the culprit.

Good luck and keep us posted on your progress.

[J P Stein]

I followed Mr. Anderson's advice for my 2.7L hot rod motor right down the line. He doesn't recommend a particular idle jet size, so I went with 60s.

A MSD 6AL, high vibration coil, & Magnecore 8.5 mm wires, NGK bp7es plugs gapped at .045......sweet, me thinks.

It took some $crewing around to get to this point. Now, I just beat on it ...I'm an AX slut.