[A98Coupe]

Akimbeau,

Engine stalling under braking is due to fuel flooding or your idle mixture being way too rich. You say you have set your mixture screws, but did you check the position of your primary throttle blades to ensure they are not exposing too much idle transfer slot? If your primary throttle blades are open too much you will be pulling main circuit fuel and cause a too rich condition. I set my primary blades so that they expose enough transfer slot to make a square shape, then I leave well alone. I then set the secondary blades so that no transfer slot is visible. I then put the carb back on the engine and adjust idle speed by first setting the idle mixture screws until I get the highest rpm or vacuum and then if I need to adjust engine idle speed, I do so using the secondary throttle blade stop screw. Of course this is all done after making sure the ignition timing is correct - otherwise you are wasting your time.

Also, after correctly setting the primary/secondary throttle plates, you should make sure that your idle mixture screws have proper control over your idle mixture. After setting the idle mixture where you get best engine rpm / vacuum, you should be able to wind them out and cause the engine speed to drop and run rough. This proves that the idle feed restrictor (IFR) in the metering block is the right size. If the engine does not respond to winding out the mixture screws, then your IFRs will need to be enlarged either by drilling in 0.002in steps or replacing the small brass jets if your carb has adjustable IFRs. If you find you cannot stop the engine by winding the mixture screws in, this again indicates your throttle blades are open too much and the engine is pulling main circuit fuel.

Another things to consider is cam size / duration. A large duration cam may need the primary / secondary blades to be opened too much to keep the motor running due to poor fuel/air density. This will uncover too much transfer slot and cause main circuit fuel to start - hence too rich. This is where you need to start drilling holes in the primary throttle blades so that you can close them back to the correct position again.

Finally, for carb tuning, I would strong advise you install a wideband O2 sensor. You can then know exactly how your carb is performing throughout the rpm range and under different load conditions. Only then can you properly start adjusting your carb.

Hope you find some of this useful.

Stuart