Vacuum Advance Problem

M

metro1

Senior Member
I have a '59 Galaxie with a 292 engine. Timing with vacuum advance disconnected is set at 6 degrees. When vacuum advance is connected timing jumps to 25 degrees. When RPM is raised to 3000 the timing goes way over 30 degrees and the engine stumbles. With the vacuum advance is disconnected the engine runs fine at 3000 RPM. The vacuum source comes from the bottom plate of the carb. It's the original old ford 2 barrel carb. At idle there is 22 inches of vacuum at this port. It appears to be where the advance was always connected. I always thought the vacuum advance did not come in at idle. The vacuum advance is new and tests good. After viewing other internet articles there are a lot of people with the same problem.
 
Were you doing this parked and just reving the engie to 3000 RPM, or was the stumbling when you were driving it ? If it was parked when the stumble happens, then it probably won't be there when driving since the vacuum will be much lower under a load.
Still, I don't think there should be vacuum at idle. I belive the throttle has to be opened slightly to get vacuum to the distributor, but not 100 % sure on that.

Sal
 
That vacuum fitting on the bottom plate of the carb is obviously direct from the intake manifold. You need to find the 'ported' fitting on the carburetor that gets it's signal from above the throttle plate.
The vacuum signal at that port will be quite a bit lower at idle and gradually increase as the throttle plate opens.

I don't have a handy example photo of a 2bbl carb but it may be similar to this 4bbl example...
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  • '57 List 1273 pass side, dist vacuum fitting.jpg
    '57 List 1273 pass side, dist vacuum fitting.jpg
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dmsfrr said:
That vacuum fitting on the bottom plate of the carb is obviously direct from the intake manifold. You need to find the 'ported' fitting on the carburetor that gets it's signal from above the throttle plate.

The vacuum signal at that port will be quite a bit lower at idle and gradually increase as the throttle plate opens.

I don't have a handy example photo of a 2bbl carb but it may be similar to this 4bbl example...
.
Click to expand...

Here is an early FORD 2100 ported vacuum source photo -

491533


The DIST vacuum signal has to be sourced from above the throttle plates (ported). A source below the throttle plates will be full manifold vacuum.
 

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  • PORTED VACUUM SOURCE _1 - Metal Line To DIST.jpg
    PORTED VACUUM SOURCE _1 - Metal Line To DIST.jpg
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All I've ever done to check the ported source is put my finger over it. I've never noted any vacuum at idle. Certainly it's not enough to activate the vacuum advance.
 
If CURB IDLE is not correct and has high RPM, there will be a vacuum signal. That's why you always disconnect the vacuum signal before setting basic timing.
 
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