An appeal for help

[Ian Williams]

Mick I would suggest you have the wrong needle profile, almost all SU needles are the same diameter in the idle position, you set your idle mixture by adjusting the position of the main jet, however the mixture throughout the rest of the rev range is controlled by the Needle profile. What happens so often when people fit an SU is the get a needle which is close enough for the car to run then adjust the cruising mixture by moving the main jet, more often than not this results in an over rich idle mixture. The fact that your engine dies when the throttle is opened quickly suggests the mixture is too weak, as a check richen the mixture by lowering the main jet if this helps you need a richer needle. Alans suggestion that the damper is not function correctly may also have a bearing, the damper slows down the rate of piston rise helping control the mixture transition as revs increase.
What has been done to the engine other than open up the inlet tract?