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Discussion Starter · #1 ·
i have my idle down to 800 and the vacuum advance is already cutting in. if i unplug the vacuum line to the distributor i have 10 degrees timing. When i plug the line back on it jumps to 18 degrees.

i have heard of the vacuum cans not working at all, but this much at 800 rpm's?

this is a dist converted from points over to electronic. i am unsure what this distributors actual advance curve or rate of advance for cetain rpm's is though.



Post Edited (Oct 5, 1:21am)
 

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I don't think your distributor is pulling to much vacuum BECAUSE it IS BEING PULLED too strongly perhaps by a carb that needs a new gasket or... Norm K.
 

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Vacuum advance should be "ported vacuum". This means vacuum increases with air flow.

Typically small holes in front of the TB plate is where the ported vacuum starts. As you open the TB plate, the air flow over these holes causes the vacuum at the distributor.
 

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Discussion Starter · #5 ·
the vacuum hose is hooked to one side of a T fitting and the other 2 sides of the T are going to (1)the top of the SU carb and (2)the port on top of the intake.

maybe the dist vacuum line should only be going to one port somewhere and not hooked into a T fitting pulling off 2 locations?
 

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It's hooked up ALL wrong. The dizzy is hooked to the front carb fitting all by itself. Plug off that other one on the intake.

BTW ported vac isn't "vacuum increases with air flow". What ported vac means is there is a port in the carb just ahead of the throttle plate so at idle there is no vac, at part throttle it gets full manifold vac and at WOT there should be none. BTW full vac advance at idle can do wonders for the idle quality of a car with a warm to hot cam in it. Once you touch the throttle, it doesn't make any difference if it's connected to the carb or the manifold.
 

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Discussion Starter · #7 ·
ahhhh, thanks!

when i looked at that T fitting today i thought why did the previous owner before me put a T fitting on there like that when both ports are pulling vacuum. i think the port off the intake itself is not ported. there must have been some reason the other owner did that.

ill fix it in the morning and probably have to redo the idle since it will be back down to 10 degrees at idle instead of 18 degrees or so.
 

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I measured the vaccum on my ported line while hand revving and it increased by opening tb and increasing flow. I'll check it again. I was only going up to 3krpm and was hitting ~ 6 to 10" below manifold vacuum at idle
 

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Discussion Starter · #10 ·
Put the vacuum line on the right way and now the car idles finally at 750-800 rpm's. at 10 degrees initial advance. before it was at 20 degrees at idle at 1000 rpms. i also suspected the way it was hooked up it was also pulling vacuum OUT of the front SU carb cause it was T'd into that port on the intake which was very high vacuum.

thanks much everyone.
 
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