no vacume from carb

[73 challenger 440]

ok, today my dad went to sync my carbs, he noticed that there was was no vacume readings from both ports, if you look in the pic you can see where I have the distributer vacume hose and at the other end of the carb I have a vacume plug over the port, both carbs have no vacume from these sources, I do have vacume for thebrakes though.. what aren't I getting vacuem at those ports?

[Chryco Psycho]

1 of the two ports will have no vacuum at idle but it will increase as RPM rise , the other port should have vacuum at idle , possibly the gasket is blocking the port ?

[ShelbyDogg]

73Ch440,  You can't really balance those 2 carbs with a vacuum guage like a milti carb setup on a bike. Those both have common plenum on that dual plane intake. Is you want to do it right, hook a progressive linkage like the ones found on the dual carb Hemi engines.  The first carb is pulled open till about half way, then the second carb opens up so that they both are fully opened at wide open throttle.   Just like a huge 4-BBL Carb.     You'll get a better vacuum signal for cruising around.

 Any one want to send a pic up of their hemi linkage?

Rob

[73 challenger 440]

my dad had the same thought.. they originaly sent me wrong gaskets, they then set me replacement ones, any suggestions on the correct gasket I would need? I opened the car up on the highway and it started pinging, my Dad was sure the timing was right on, but thinks because of the lack of vacume there was no advance in the distributer, causing the pinging, is he right??

1 of the two ports will have no vacuum at idle but it will increase as RPM rise , the other port should have vacuum at idle , possibly the gasket is blocking the port ?

[ShelbyDogg]

How much advance did he put into it? Try about 6 degrees to start.
If you know that the timing is right, try backing off the timing a few degrees. If it still pings, try it without the vacuum advance hooked up. If it still pings, try racing fuel from the drag strip.  It won't ping. Run super-unleaded or put in some low compression pistons.  If it didn't ping with the vacuum advance unhooked, try hooking the vacuum canister to the vacuum that is high at idle (called manifold vacuum). with our bad gas, and high compression, you want the extra advance for idle and want it to retard when under load.  (The factory had it hooked to PORTED vacuum, but we are stuck hooking it up to MANIFOLD vacuum.   In your picture, if you don't have a smaller fitting for manifold vacuum, you'll have to get some kind of adapter to neck that plugged big one down to a smaller fitting for the smaller hose.
Rob