Yesterday I was checking the timing on my 73 L48 and the initial timing is fine. But when I went to unplug and reconnect the hose to the vacuum can on the distributor I saw no increase in idle speed. So, basically there no response when disconnecting the hose to the cannister on the distributor.
From reading on the forum you should see and increase in about 16 degrees timing advance.
Does this mean the canister is not working and maybe I need to replace it?
Please let me know your thoughts.

 

You can check the canister with a manual hand held vacuum pump to see if it holds vacuum. Another way is to force the linkage back into the canister and hold your finger tightly over the open stem where the hose hooks up. If the linkage goes back to its normal position, the diaphram is leaking and the unit needs replacement. This sounds like your problem.

 

There are three possibilities.

First, you vacuum advance may be defective.

Second, you have the vacuum advance connected to a timed port on the carb which will not give you vacuum advance until the throttle is advanced. This is the usual way for a vacuum advance to be set up. You can check your vacuum advance manually by using a vacuum pump.

Third, Early emission systems were a Rube Goldberg (yes, I'm showing my age ) of relays and temperature related ports. On my 74 L48 the vacuum is routed through a temperature sensitive vacuum port that only allowed vacuum advance when the engine was warmed up. It also was routed through a switch on the 4 speed tranny that only allowed vacuum advance to occur when the tranny was in 4th gear. When the tranny switch was actuated it opened a solenoid on the intake that allowed vacuum to flow through the previously mentioned temperature related port and into the vacuum cannister. I don't know if your 73 is the same but if its stock it may have this type of setup. I got rid of all that crap and my vacuum advance is now connected directly to a timed vacuum port on the carb. The car runs 1000% better this way. To be sure, check the vacuum advance with a manual pump. They are very cheap and can be used to check a lot of other things on the car like the headlights and vacuum doors on the heat/AC system.

Good luck.

 

I agree with both above posts.
When you pulled the hose off the dist. did you put your finger over the end and confirm you had vacuum? Also check inside the dist. to see if mechanically the vac. advance is restricted from moving for some reason.

 

Thanks guys.

I will check tonight how the vacuum is routed.
I will also check the vacuum when I put my finger over the hose.

 

If you have vacuum supply on the dist. line at idle..and still get no change in advance, either the vacuum can is bad or the mechanism in the distributor is frozen up [or disconnected internally].