Spider Idle/vacuum/brake Problem

[shemogue]

Can anyone help me with this one. I have an 85 Spider with Dellorto conversion. I warm up the car and set the idle to 900rpm. Then when I push on the brake pedal the idle drops by half and the engine wants to stall. I checked the oneway valve and it seems to be fine. Vacuum hose is good too. If I shut the engine off, pump up the brake pedal, hold it and start the car it does go down but not very much. When I drive the car and and brake the pedal is hard and the engine wants to stall. I thought it may be the booster but when I went to start the swap I removed the vacuum hose from the booster and there was a ton of suction. If the booster is shot would there still be so much suction? Is there anywhere else I should look before I start the booster swap?

Cheers

shemogue

[Tifosi]

The booster can still hold vacuum even when it's on it's way out. (been there, done that)

[ghnl]

Remove the hose & cap off the fitting at the intake - taking the booster out of the equation. Drive the car (carefully - you will not have 'power' brakes) and see if makes any difference. If not, it ain't the booster.