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Weird vacuum advance issue


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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...

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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.

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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?

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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

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  • 2 years later...
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?

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