Vacuum Line

[66 coupe]

I have a '66 Mustang with a stock 289 and Holly 2bbl carb. Could someone please tell me where the vacuum advance valve hose should connect? I have tried connecting it in two places with different consequences. When I connect it to the outlet on the upper right hand side of the carb the car idles great, but hesitates when you accelerate from a stop. When the hose is connected to the manifold the car idles very high. In both locations the car seems to surge as your driving. The car has a late model distributor with Duraspark and a vacuum advance. I have a picture of the carb but don't know how to attach a picture.

This ad is not displayed to registered or logged-in members. Register your free account today and become a member on Mustang Forums!

[kalli]

per stock it goes to the upper right hand one. This one is called ported vacuum. the other one is called manifold vacuum and you can tell the difference that the manifold vacuum is high in idle (you can feel the carb sucking through there) and the other not.
Some people use manifold vacuum for their setup, but this needs readjusting timing and curb idle speed. the theory being that at WOT you don't have any vacuum, hence no ignition advance from the vacuum port.

for you i'd suggest to use the upper right hand one.

The hesitation from stop can have several different causes:
a) wrong ignition timing
b) low float level. check the holley website or google on how to adjust the floats for your carb. most holleys have the adjustment on the top front of fuel bowl
c) running to lean at idle (try richen up the idle opening the two screws at the front metering block) by half turn and see if it behaves different. one of the screws is directly below the upper ported vacuum port and the other one is on the exact same spot on driver side of carb.
d) the accelerator pump is not working or misadjusted. with engine off remove air cleaner and look down the top of the carb. when engine is hot the top butterfly must be fully open (no choke). and when you open the throttle you should see two sprays of fuel shooting out the top of the carb (as you turn). if it's not doing that at all i'd say the accellerator pump might be gone. if it sprays check on google or holley on how to adjust them correctly

enjoy ...

[capri man]

the one on the carb is the correct one. check your timing.

[Jonk67]

Also check the vac. adv. on the dist., the internal diaphragm may be rotted or punctured. Remove the dist. cap and find the 'arm' that comes out the back of the vac. adv. and connects to the dist. plate, put the hose on the vac. adv. and suck on the end of it hard as you can - you should see the arm pull into the vac. adv. and stay as long as you keep vacuum on it. If it doesn't move or slowly goes back out while you're holding vac. the diaphragm is bad. They sell replacements at most parts stores ~$15.
If this is the case it also causes a vac. leak in the system. Even if it a newer rebuilt dist. it only takes a minute to verify that it's working. This normally only causes issues at higher RPM's as it doesn't advance the dist. timing.
Jon

[kalli]

Originally Posted by Jonk67

Also check the vac. adv. on the dist., the internal diaphragm may be rotted or punctured.
Jon

he said when he connects vac advance to manifold vacuum the idle increases. This will not be the case with rotten diaphragm ;-)

[66 coupe]

Kalli, Thanks for your advice! I adjusted the screws as you suggetsed and it's running much better. I still have a very slight hesitation, but nothing like it was. My next project is trying to get the car to run cooler. Sitting at a stop light it starts to get quite warm.