I have dismantled the carbs for a rebuild but having a hard time trying to get the engine to idle smoothly. The carbs are Weber DCOE 72/73 on a 2ltr engine.
Car was working fine before dismantling. The only significant hardware I changed was the needle valve (no 83 in the image below) which was replaced with a new one of the same size (1.5) and the washer (no 82) behind it as for some reason there wasn't a washer before. I have re-calibrated the float to 7.5mm. Other insignificant hardware were the bearings, rubber washers, gaskets etc.
I have calibrated both carbs by shining a light into the trumpet hole and checking the butterfly in relation to the progression holes. These carbs have 4 progression holes and the butterfly was sitting right on top of the 4th hole.
Carbs were installed on new rubber mounts and gaskets, and also used a thin layer of RTV on all faces to get a 100% seal.
I started off by turning the Idle speed screw IN 1/2 a turn and mixture screw OUT 3/4 turn.
The car did not want to idle and had to turn the idle speed screw IN 2 1/2 turns to get it idling just around 1000rpm but the engine runs very very rough.
Turning the mixture screws OUT 2 turns from home did not make a difference. The funny thing is that at one point the engine revved to around 3000rpm without even touching the throttle. I waiting for around 10 seconds and it did not go down. Switching off the engine and back on solved the over revving.
Driving the car at partial throttle looks good except for another instance where that the RPM climbed up again and had to switch the engine off.
Why does it decide to rev up on its own ?
I have read this thread and some suggested that the mixture screw needs more turns OUT. I haven't tried this yet. Any other suggestions please?