Weber tuning

[Roger 911]

I have a 2.4T with E cams and Webers, vac advance distributor w/ Pertronix, and a twin pipe sport muffler. I'm pretty sure the jets are; 32, 135, 180, 60, F3. The motor runs great at high RPMs and under load. The timing is correct (w/ vac on), valves adjusted, and the carbs have been synced.

Issues; 1) the transition from initial throttle to mid range seems a bit rough, i.e., after accel pump, but before mains, 2) popping under deceleration, 3) I can't get an even idle under 1200 rpm.

Thoughts; I have a set of F26 tubes. Would these make a significant difference in the transition? Should I simply disconnect the vac advance and try getting the idle down to 900? Will this cause any other problems?

[Evans, Marv]

Can't say much about the idle, but my 2.4E motor popped on deceleration, and it turned out that it had 28 or 30 mm venturis. Replaced them with 32mm & it ran fine.

[Steve@Rennsport]

Hi Roger:

First, lose the vacuum advance and make it a pure centrifugal unit only. Set the timing so you have 33-34 deg total at 6000 RPM. You should have around 10 degrees at idle; 900 RPM.

Second, check your accelerator pump volumes. Sometimes they need tweaking although with 60 idles and F3's, you are not lean. You also might try 55 idles to see if that makes things better or worse.

Third, make absolutely certain that you do not have any vacuum leaks between the carbs, manifolds, and heads. Test with a can of carb cleaner.

Fourth, remove the idle jets and main jets and blow out the idle jet passages with clean compressed air. The tiniest piece of smurf can cause the symptoms you have.

Lastly, make sure that your fuel pressure is 3.5 psi and your float levels are perfect, by the sight glass gauge with the engine running.

A bit of tweaking with the idle mixture screws should do the trick, unless your throttle shaft seals are leaking air.

[Zendalar]

Steve..

I am still in middle of my EFI project, so i need to stick with my carbs for a while.

I have a plain T, with 27mm venturies, and the car runs crappy. Idle jets are 45, emulsion tubes F26..hmm..mains 120, air correction 180.. What are your opinions on this? If i change to 55 idle jets the car runs very poorly.

You think I should loose the vacuum as well? I also thought to bore the venturies to 30mm.. Any ideas?

[Roger 911]

Steve,

Thanks for the info. Question; "lose the vacuum advance". Does this mean simply disconnect the vacuum line and plug it, or does it mean having the distributor modified to be mechanical?

[john70t]

and where can you get measuring tubes for the accelerator pumps?

[araine901]

I know Performance Products sells them. It is simply a 1cc graduated vial. I rigged up a piece of saftey wire to "dangle" it down there in an secure manner. It seems a bit caveman at first, but you need to dangle the vial directly under the pump jet and do a single full cylcle o the linkage and see how much sqirted out. Then you adjust the tiny acc pump jet linkage as needed.

I totaly agree with Steve on his recomendations. He went down the list like the old pro that he is. And he is not kidding about the idle jets. It only needs to be a tiny piece of stuff to ball you up. You need a good fuel filter with webers and old cars with old tanks and lines.

[Steve@Rennsport]

Zedalar:

Never simply bore existing venturies; you will not be able to maintain that VERY critical shape and inner contour. Get new ones in 30mm.

My best advice would be to find out WHY its running poorly before you make any wholesale jetting/configuration changes. Go through the list in detail:

1) Adequate fuel pressure & volume at the carbs? If the in-tank filters are clogged with rust, it will not run well.

2) Float levels perfect at 3.5 psi? Any leaking needles & seats?

3) Any air leaks at the throttle shaft bushings? If they leak air, its damned near impossible to get the idle mixture screws to respond.

4) Check the usual stuff: vacuum leaks, ignition timing, valve adjustment, plug wires and connectors.


Roger:

Disconnect and plug the vacuum lines to prevent leaks. If the distributor is not worn, you can set the timing to the specs above. If the idle timing wanders, install a Pertronix Ignitor to eliminate the points and provide FAR more stable timing and a smoother idle.