I've been playing with my Weber 40's for a couple years now and am pretty happy with the setup. Then I took it to a local chassis dyno to see how I had done. The engine runs pretty strong for a 1911. However, the torque curve has a good size dip from about 3200 to about 3600 rpm and then takes off and stays pretty flat until the valves float at 5700 rpm. The AFR goes super rich during this dip in the torque curve. We made 5 runs with 4 different jets. The richer jets (135 & 145) enlarge the dip. The leaner jets (125 & 130) do better but I'm still losing about 5 ft-lbs of torque and they go really lean on the top end. I'm not sure if I can get rid of this dip. It may be mostly form the "tune" of the mechanical components of the engine. I'm thinking of trying a different emulsion tube to see if I can lean out the bottom end some. This has been a very educational experience. The engine is pretty tolerant of AFR: anything from 12.0-14.0 seems to run pretty good. When the AFR gets out of these bounds you can see the torque fall off relative to the other runs.

Present settings: 40 idf, 32mm vents, 55 idles, 125 mains, 200 Air correction, f11 emulsion tube.

What I would like to try is a different emulsion tube and then go back and work with the mains and air correction.

Has anyone run anything other than f11's?? Any suggestions for an emulsion tube to get a little leaner bottom end?


OBTW, I've dropped the engine and am dealing with the valve float issue. It's driving me crazy.

I would try 175 airs before going to a F7 emulsion tube.
Also maybe get a bigger squirt with the accelerator pumps.
I set them at 7 turns in from the end.

I am no expert at this, but maybe your venturis are a little large??? I am running a 1911 and have 44s on it, and I am pretty sure that the 32 vents that I am running are too big.

Bill did you shim your valve springs to get maximum open pressure? We set your heads up to default specs, which can handle up to .500 lift. Since you are running way less than that you can add a good deal of shim. That will raise your mechanical rev limit.

porche914gt & KaptKaos: The problem is that I'm too rich at 3400 rpm. more accelarator pump and smaller air correction is going to make it richer!!

what does a F7 emulsion tube do?

Len: I've got some stiffer valve springs from Fat Perf. They are substantially stiffer and I should be able to find out how high this thing wants to rev. I know the added friction may cause some loss of torque and added wear to the cam, but I've got to try them. Thanks for the help.

There's a good chance the excessive richness in one rpm range is due to your exhaust configuration.
I don't think switching to f7 emulsion tubes will solve the problem.

From what I have heard, the F7 tubes have better transition.
Given the RPM range that you are feeling the issue, it sounds like the F7 tube may work better, but I would get Jake and Len to help..if you have Len's heads...they should know the perfect setup for the motor...I would assume Jake has tried every carb setup...

Rich

Bill,

I don't really have any valuable info for you
I can't comment on the F7's

but on my IDS carbs... we tried 3 different emulsion tubes on the dyno
emulsion tubes make a big difference in transitions
I can't comment if the F7 will be better or worse, but it will be different.

brant

Actually, I wasn't planning on going to F7's. That tube was mentioned by porsche914gt. From what I've read the F7 would actually richen the low end. The emulsion tube that I am considering is the F2. It's supposed to give a leaner low end and throttle response. I found one site that actually made emulsion tube recommendations based on cylinder capacity! The F2 was for 450-575 cc's. They recommended F9 and F16 for 350-475 cc's. Form what I recall, Jake uses the F11. I was just wanting to hear of other's experience with emulsion tubes. I'm a CSOB and the emulsion tubes are a lot more expensive than jets. If I'm going to put out the big bucks, I want to make an intelligent choice.

call aircooled.net
They were awesome and had documented configurations for lots of motors.
they also will swap jets, tubes and venturis till you get it right.
They did for me.
You can try a setup, if it does not work, send them back, get another set and try again.

Rich

Good suggestion! Thanks!