what is your setup?

single 40DCOE or twin 40DCOE?
A12 or ??
Modified?

Air correctors - too lean (large hole) causes a miss at near max RPM, too rich (small hole) it will be soft and not give full power
Main jets - affect max RPM similar to air correctors
Emulsion tubes - affect the acceleration phase from progression onto full throttle and the main circuit coming into operation
Idle jets - affect alot! idle, off idle and progression onto the main circuit are all determined by this!
Aux venturi - also important for response
Choke - as mentioned sets the effective rev range of the engine
Accel jet - purely there to fill the hole created with sudden opening of the throttle causing a lean spot, you should be able to drive without these if the throttle is opened gently enough, don't use them to hide a weak progression!

For the low-speed circuit, follow Weber's easy advice: http://www.redlineweber.com/html/Tech ... ment_layout_typical_i.htm

there is plenty of good info out there but the main thing is to only work on one area at a time.
If you can get access to a wide selection of jets for tuning it will make it a lot easier and quicker (especially if you only need to pay for those you eventually "keep").
If you can find someone that knows these carbs and has a dyno, you will get it nutted pretty quickly but at $$, doing it yourself will take longer (but is satisfying and cheaper (maybe, if you don't blow anything up and don't have to buy heaps of jets !)).

Hope you can sort it out and good luck!

> These are new carbs I never touched them yet.

Have you set the idle and mixture screws for best lean idle? If not it won't run correctly. Weber explains how to set best lean idle here.


> I bought 28mm chokes ... I think I need to use a 165-180 air corrector jets and Main jets 110-130.

That's a HUGE range. Start with 28*4 = 112 main jet and 168 air corrector.

I would be looking at two areas that will influence part throttle [cruising] stumble /popping conditions. 1, as already suggested above is the incorrect choice of idle jet. As already stated the idle jets meter fuel for the idle and progression ccts, which by the way is 80 -90 % of most of your driving. WOT is rarely used in the scheme of things. 2. poor carb balance between carbs will also produce similar symptoms. A carb balancer /synchroniser will be your best friend to sort that out.

After reading the weber adjust page really opened my eye's on how much goes into tuning these carbs. I realized that my mixture screws are 2 1/2 turns out way to much so according to weber my idle jet is to lean.