Weird vacuum advance issue

OK, this is with my '65 300 with AFB...

I reset my timing today to 12* initial, which leads to about 30* total at 3500 or so RPM. It's got manifold vacuum, which adds 11* timing at idle.

When I unplug the vacuum advance at the canister, the engine doesn't slow down, even without the vacuum advance timing added. If I plug the hose to stop the vacuum leak, the engine loses about 40 RPM.

However, it does not want less idle mixture; it will lose RPM if I turn in the idle screws.

What the heck?

On a semi-related note, I just had the radiator cleaned out, and it now seems to run 190* most of the time going down the road, but will almost immediately climb to 200+* at idle. It even hit 215* idling in the garage. It has a 6-bladed clutch fan with a good clutch, and a shroud. Any other ideas there? It will cool down if I rev the engine, but not as much as if it were going down the road.

I should mention that it has a 3-row brass crossflow radiator...

Shouldn't the timing be 2.5 BTDC???? Had an issue with my 300, but it was pinging on accel, long story short, carb had a crack in it and was dumping gas in the vacuum advance. Maybe this is a common problem on Carter AFBs although I replaced it and that was that..

As for the radiator.. have you had the flow checked by a shop?? Mine looked great, till I had it checked... 30% blocked.

Yep, just had the radiator cleaned and it's fine.

I actually was thinking the same thing about the carb...I'm glad you were able to back that up with a similar occurrence!

As far as the timing, it seems to like a lot of initial advance, so I adjusted the curve. What kind of AFB did you replace it with?

It sounds to me like your vacuum advance is bad. pull the hose and check how much timing you have , and then attach the hose and see ifthe timing advances. If it doesn't, you have a bad advance. When you block the carb hole and the RPM drops, tells me that the advance has a ruptured diaphragm

What kind of AFB did you replace it with?

Another stock rebuilt Carter. I am trying to keep the car as original as possible.

OK, this is with my '65 300 with AFB...

I reset my timing today to 12* initial, which leads to about 30* total at 3500 or so RPM. It's got manifold vacuum, which adds 11* timing at idle.

When I unplug the vacuum advance at the canister, the engine doesn't slow down, even without the vacuum advance timing added. If I plug the hose to stop the vacuum leak, the engine loses about 40 RPM.

However, it does not want less idle mixture; it will lose RPM if I turn in the idle screws.

What the heck?

On a semi-related note, I just had the radiator cleaned out, and it now seems to run 190* most of the time going down the road, but will almost immediately climb to 200+* at idle. It even hit 215* idling in the garage. It has a 6-bladed clutch fan with a good clutch, and a shroud. Any other ideas there? It will cool down if I rev the engine, but not as much as if it were going down the road.

I should mention that it has a 3-row brass crossflow radiator...

hey man i could really use your advice, today i tried putting a new set of points in my 65 with the 300, i then adjusted the gap to .016 with a feeler gauge and reassembled the distributor, after this i installed a tach so i could check the rpms, i then set the idle with the choke off, vacuum advance disconnected and plugged up to prevent vacuum leak to 550 rpms with the screw connected to the throttle, after this i put the timing gun on and adjusted the timing to 2.5 degrees on the scale with vacuum advance still disconnected and plugged, after all this i tightened the distributor down plugged the vacuum line back into the vacuum advance and took it for a spin and needless to say she still feels about the same, i haven't adjusted the mixture screws yet because it was getting dark on me but i dont think they single handedly would make it run the way it is although i could be wrong, when setting the ignition timing do i do that at the 550 rpms or lower then set it to 550 afterwords? and what should the idle speed be set at after all this is that the 550 rpms?