Idle goes up

[MountainMan73]

Having a new issue trying to get my fathers Dart going. Put a new carburetor on (street demon) set it up best as I can. Car runs pretty good at idle in drive etc. Issues is when I press on the brake pedal the idle goes up. I took the check valve off and it appears to function correctly. I cant suck air through it and if I try the other port thats plugged air flows through. I dont see or hear any leaks. Any ideas??

 

[RustyRatRod]

Where is the booster hose attached at the engine?

 

[MountainMan73]

Where is the booster hose attached at the engine?

To the left back port on the intake. Its a edelbrock intake I don't know what the model of it is.

 

[AJ/FormS]

>If the idle speed goes up and stays up with the pedal partially pressed down or more, then the diaphragm has a hole in it.
>If as soon as you lift off the pedal, the idle returns to normal, then the valvebody/control-valve is faulty.
>If the brake pedal is extremely touchy, giving you full assist with the pedal barely pushed down, then;
1) either the control valve is broken, or
2) the pushrod is way too long.
> If the booster offers very little assist, with no other symptoms, then the pushrod is too short
>during Normal operation, the booster should barely affect the idle.

I have had no luck with the booster evacuation hose routed to just ONE intake runner; I always get a perceptable dip in rpm, whenever I stab the pedal.
Your carb should have a port for it, on the backside that goes directly into the plenum(s). If it doesn't, I'd put one on the plenum itself. It's a drill-it and tap-it deal.

 

[MountainMan73]

>If the idle speed goes up and stays up with the pedal partially pressed down or more, then the diaphragm has a hole in it.
>If as soon as you lift off the pedal, the idle returns to normal, then the valvebody/control-valve is faulty.
>If the brake pedal is extremely touchy, giving you full assist with the pedal barely pushed down, then;
1) either the control valve is broken, or
2) the pushrod is way too long.
> If the booster offers very little assist, with no other symptoms, then the pushrod is too short
>during Normal operation, the booster should barely affect the idle.

I have had no luck with the booster evacuation hose routed to just ONE intake runner; I always get a perceptable dip in rpm, whenever I stab the pedal.
Your carb should have a port for it, on the backside that goes directly into the plenum(s). If it doesn't, I'd put one on the plenum itself. It's a drill-it and tap-it deal.

This just opened a can of worms then. So the pedal to me seems super soft you have ot press pretty dang hard and when you pump it it really dont get "stiff" As well as soon as I let off the pedal it goes back down to normal idle. Sounds like I might be replacing it. It does have the 73 disc conversion on the front fi that even matters.

 

[RustyRatRod]

My truck idles up a HAIR for about 2 seconds when I depress the brake pedal, then it drops right back down. If that's what yours does, it's normal operation.

 

[MountainMan73]

My truck idles up a HAIR for about 2 seconds when I depress the brake pedal, then it drops right back down. If that's what yours does, it's normal operation.

No it stays up forever how long I have the pedal depressed

 

[RustyRatRod]

No it stays up forever how long I have the pedal depressed

Then I will agree with @AJ/FormS 100%. There's a hole or tear in the diaphragm.

 

[MountainMan73]

Then I will agree with @AJ/FormS 100%. There's a hole or tear in the diaphragm.

Thanks for your help and advice!