Weber butterfly angle

[rideaway]

Hello everyone,

I have not been able to find a definitive answer on the forum or on the internet.

I'm having some trouble tuning my carburettors Weber 40 DCOE 31 after an engine rebuild. The transition is poor and causes jerking. Looking at the position of the throttles in the bodies, the first progress hole goes from completely blocked to completely unblocked. Also on the same carburettor the position of the butterflies is not identical. I had previously adjusted the balance with the Airflow syncrometer.
On one of the carburettors, it seems that the throttle cannot close in the correct position. Once closed, some of the throttles show an opening.
I'm thinking, on the one hand, of twisted shafts, but I wonder which butterflies are fitted originally. Mine have an angle of 79.30° with holes (of different sizes depending on the body).

What are your opinions?

I hope the translator has converted my text into something understandable.

Regards
Stéphane

[Craven]

Correct, 79.3 DCOE 31 with air bypass, have only seen one size hole would seem yours have been played with, 78 deg on 151.

[elans3]

Sounds like you have a twisted throttle shaft. You can "untwist" them with some careful spanner application. Carbs need to come off to do it successfully though. If a shaft is twisted, no amount of attempting to balance with the synchrometer will work, until the shaft is either renewed or straightened.

[rideaway]

Hello,

Thank you for your answers.

After having said several ‘’‘%&%@&’' to unscrew the already damaged butterfly screws, I seem to have detected the problem.

The PO had the carburettors rebuilt by a ‘specialist’, which led me not to touch them when rebuilding the engine.
The holes in the butterflies are bigger than the fixing screw, so it's possible to screw them in when they're not properly in place, which prevents them from closing properly.

Best regards
Stéphane