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Weber on Opel Commodore
geschrieben von: Fredrik ()
Datum: 24. April 2011 21:03


I’ve just replaced my double Zenith/INAT 35/40 on my Opel Commodore having a 2.5 litre six-cylinder engine, all-original. Instead of the Zeniths I have put on double Weber 40 dfav carburettors (Ford Capri V6). Why? Beacause the Zeniths are ok but the engine really has a lot more performance (specially torque) hidden behind those original Zeniths. The Weber carbs have been cleaned in ultrasonic batch and put together with new gaskets and jets by myself. The jetting is based on information from a reliable source (Weber carb selling company for many years) but since it was very long ago since this was tried out there is no one to ask for trouble shotting or help.

However, with the Webers on some things are good and some things are not. I mainly have two problems:

The idle is too high, around 1100 rpm.

The idle screws are not even in touch with the throttle levers, still high. The choke works fine, no fast idling affecting the idle when warm. High idle not affected by disconnecting the linkage. Idle is not uneven but could be better. Idle mixture screws do not respond very much when turning them out, to some extent in (starting point one full turn out). Idle jet size is now 70, when trying size 50 the idle is till to high but the engine go worse/low rpm if I turn them in compared to size 70.

The engine hesitates for one second when I go from idle/static pressure on pedal to acceleration, and then it pulls strong and runs great.
Accelerator pump jets (size 70) leave nice fuel jets. Changing idle jets from 70 to 50 made the hesitation much worse. Linkage seems to be quiet synchronized and not warp.

I need help to sort this out. My one ideas are around vacuum leakage although both carburettor “feet” and inlet manifold have been polished against a flat glass surface with a sanding sheet until they were flat, mounted with new gaskets to a torque of ~ 12Nm. Cant find any leaks with “starting gas”. Another idea is to increase idle jet size to solve the acceleration problem but I guess this would not help the high idle.

Grateful for any ideas and support of what could be wrong.

Best regards


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Weber on Opel Commodore 953 Fredrik 24.04.11 21:03

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