No vacuum from carb

[clazar]

I have a 440+6 auto. I removed the center carb to reolace the accelerator pump diaphram. When i started the engine after i was done, i noticed the idle was about 1100 rpm's. No adjustments would lower it down to the prescribed 900 rpm's. After looking everything over i noticed there is no vacuum from the center carb to the distributor. I believe there is supposed to be some, right ?? What can have gone wrong or am i just missing something so obvious.

Chuck

 

[67 B-body]

Vacuum leak at the carb base...

 

[lewtot184]

the linkage that ties the 3 carbs together is probably out of adjustment. check to see if the connecting rod to one of the end carbs is too tight and is letting the throttle on one of those carbs crack open.

 

[clazar]

Vacuum leak at the carb base...

everything is tight on base. i didn't take the carb apart except to change the diaphram on the accelerator pump. Gasket is good at the base. your answer is probably right, but where do i look for a leak???

Chuck

 

[clazar]

I went & checked the outboard carb linkage & it was adjusted wrong. Easy fix. Idle is ok & adjustable. But still no vacuum to distributor. Center carb has a lower vacuum line to vacuum pot for possibly choke maybe. I checked that line & it has vacuum. It comes from center carb in front & at the base. How could 3 carbs not have vacuum from their ports???

Chuck

 

[440+6]

The port that goes to the distributor will not have any vacuum at idle, but if you open the throttle part way you will start to get vacuum, that's how it works.
Don't mix up the three ports.

 

[clazar]

The port that goes to the distributor will not have any vacuum at idle, but if you open the throttle part way you will start to get vacuum, that's how it works.
Don't mix up the three ports.

You're absolutely right. I took the vacuum line off the distributor & gave it a little gas & got vacuum. I don't know why i thought there should be vacuum at idle.

Thanks
Chuck

 

[Meep-Meep]

The distributor vacuum is a ported port, meaning it's manifold vacuum but only present when the throttle blade is open a few degrees. Ideally the angle of the throttle blade where vacuum is available should be about what you need to keep you going on a flat freeway. If you did have vacuum at that port at idle then it's highly possible your timing is retarded and the throttle is open too far to compensate for the low idle.

 

[clazar]

The distributor vacuum is a ported port, meaning it's manifold vacuum but only present when the throttle blade is open a few degrees. Ideally the angle of the throttle blade where vacuum is available should be about what you need to keep you going on a flat freeway. If you did have vacuum at that port at idle then it's highly possible your timing is retarded and the throttle is open too far to compensate for the low idle.

Thanks for your answer. I kept thinking there should be some vacuum at idle. I should know better.

Chuck