Weber jet recommendation Options

[Eric_Shea]

Happy to help. I went through so many carb woes, I developed a spreadsheet using all of the calculations from the Weber books etc.

With our new division, PMB Motorwerks, Gene and I have come up with some killer 2056 big valve motors, and a carbed 2270. Quite a few of these 2056's are carbed. At our altitude (4300) carbs and jetting can be a "stimulating" experience. The spreadsheet has been refined over time and has really proven itself.

You probably have one of the 86 grinds. You are leaving a "lot" on the table with your current jet and venturi combo. You'll love the way it drives once you get everything set up.

[Darren C]

Many thanks Eric, much appreciated I'll give that combo a try.
SKL, apologies for hijacking your thread, but I thought it might be best to keep all the jetting questions in one thread rather than start yet another with the same request for help!

[CG-914]

Couldnt agree more with Eric!

Also if you have trouble getting of idle, you should check if you are too lean in that moment. Check your excelerator pump jets, if you make them bigger you still get the same amount of fuel from the pump but delivered quicker. Another method would be increasing the size of your idle jets and turning the mixture screw in further, but then they really become hard to tune in idle!

Use a O2 sensor and do some runs to get the perfect jet set up. For idle only a CO and HC tester would give you a perfect adjusting but they are hard to come by or very expensive!

Good luck! Carbs are fun once you get more into them.

[SKL1]

Oh no, another PMB division! Another place to spend more $$ (IMG:style_emoticons/default/smile.gif)

[stugray]

Here are my notes from my racing logbook this year:

Carb configuration:

40 IDF Webers (Italian)
Venturis 28mm
Idle Jets 60
Main Jets 115
Air correctors 200
Emulsion tubes F11
Accel Bypass valve .55
Float valve set to 14mm (closed) to 24mm (open)

I since changed the mains to 120, but I dont feel much of a difference, but my AFRs dropped a little lower than necessary.
When I collect all the AFR data from a race and average the WOT data only, I get ~12.5-13.5 AFR.
EGTs never get above 1200-1300

This is with a webcam 86b. stock heads, 2056, 5000 ft. alt., 91 pump gas.
Mallory unilite, MSD 6AL 34 degrees advance at 3500.

I am considering going to larger venturis, but I run almost exclusively at high altitude, and havent sprung for the $$ new 32s.

I would LOVE to have a peek at Eric's spreadsheet! :-)

[SKL1]

Seems like CB is the easiest place to source jets, etc for Webers... The kit on my '73 came from Redline, but I've had trouble getting them to respond to inquires on line or the phone. Replaced their linkage with Chris' from Tangerine...

[SKL1]

Gonna have to see if that spreadsheet from PMB Motorwerks is available. Still playing with jetting... (IMG:style_emoticons/default/sad.gif)

Does run a little better now that timing is correct at 34 @ 3500. Valve adjustment is fine. Still falls flat when accelerating at around 3500 rpm... the saga continues.

Weird thing is my '71 has a 050 Bosch distributor, Webers, same Webcam but runs a lot better through the rpm range. It's in IA at 800' whereas my '73 is in Scottsdale at 1800'.

[michael7810]

Dougs Bugs and Bunnies over in Mesa has a good selection of jets AND you only have to buy 1 set as they will swap for different sizes for free. They're a quick drive down the Beeline from you.

[jmill]

Gonna have to see if that spreadsheet from PMB Motorwerks is available. Still playing with jetting... (IMG:style_emoticons/default/sad.gif)

Does run a little better now that timing is correct at 34 @ 3500. Valve adjustment is fine. Still falls flat when accelerating at around 3500 rpm... the saga continues.

I never understood why everyone stuck with the F11 ET. It was specifically designed to provide a lean mixture at lower velocities. Try the F7. It's the opposite of the F11 and provides mixture enrichment at lower velocities.

If you swap to the F7 you'll need to reduce the size of your idle jets.

[jmill]

The reason you have that flat spot is due to the idle jets dropping out before the mains come in (lean transition). You're trying to fix that flat spot by increasing your jet size. It helps a bit but it's not going to eliminate it. You have to do 1 of two things and maybe even both to fix it.

#1 - Smaller venturis - increase vacuum signal to the mains to bring them in sooner

#2 - Emulsion Tube - get an emulsion tube that works on a lower vacuum signal and provides a richer transition like the F7

You'll then find your idle jets are too large and you'll have to drop down to 50-55. If you go with the F7 you may even need to drop down your main jet size and step up the AC jet to lean it up at the top.