After setting up my advance curve,i noticed that the timing advanced the same way whether the vacuum advance was hooked to the ported vacuum or not.I don't think it's been doing anything .Today,i got some vacuum hose and my hand-held gauge and went for a drive with it hooked to the ported vacuum.It gets no vacuum except alittle under hard acceleration(5hg).I don't think thats enough to even move the vacuum advance at all under most driving situations.When i got home,i hooked it to manifold vac. just to see if the can worked(it's an accel adjustable one,)and the timing advanced alot differently.I've tried adjusting the can in and out and it made no difference.Running around without vacuum advance has got to be hurting my gas mileage,so can i hook it up to manifold vacuum and make it work right ?I know i have to lock out some of advance to keep the total timing down,but i think i've read that some guys swear by using manifold vacuum for vacuum advance.Any opinions?

 

Sounds like the ported vacuum passage in the metering block or
carb body or baseplate is blocked. Could be the wrong gasket in either the metering block or baseplate.
You should get little or no vacuum at idle and a strong vacuum signal at part throttle cruise that increases with road speed and decreases with load..

 

Which 650 is it?

The ported vacuum on alot of them is in themetering block, just above the pass side idle mixture screw. There should be a little tube hose nipple stuck into the metering block there, but it often comes out and then if it's a used carb, you won't even know it's there. Using either the wrong metering block gasket or putting it together wrong will block the passage off.

 

The carb is a model #4175.The carb was rebuilt by me a month ago with a Napa echlin kit and the gaskets seemed to line up with the old ones.Could a leaky power valve do anything like this?I re-used the old one when i did the rebuild.I thought it was kind of strange to not be getting any vacuum from the ported(the passenger side of the metering block,right?)source.My Q-jet even had a signal from ported when at idle.I'm going to look in to all your suggestions as i'm going to take the fuel bowl off and install a new power valve this afternoon.I know i've got to fix this because i'm using WAY too much gas and i'm taking my car on a tour in a couple of weeks.I'll let you know how i make out.Thanks for the response guys!

 

Took the carb apart this weekend to re-jet and install a new power valve,the gaskets looked perfectly aligned with all the holes,and i couldn't find anything else out of place either.I blew through the port with a piece of vac. line while working the throttle back and forth and could here the change in pitch,so i assume air is getting through in varying quantities according to throttle input.Anyway,i put everything back together and i've got vacuum now.Maybe something was stuck in there and i blew it out,i don't know, as long it's working,thanks guys.