Vacuum advance for civilian distributor on a stock M725 engine

[MJCougler]

I have a civilian distributor on a military engine. I have the 1-barrel Holly 1920 carburetor. There is a sticky on M715zone.com about the vacuum advance for the 2-barrel carb. It is a nice write-up, but it does not help me. The fire department mechanic tied the vacuum advance line to a "T" tap on the side of the head behind the intake manifold. This is the same tap where the large vacuum line goes to the vacuum section of the fuel pump for the wiper vacuum. At idle, I am getting 30 inches of vacuum at the vacuum advance (maximum reading in the coasting range) on my vacuum test meter. . And, based on the “sticky” article, that is not the best place to tap off the vacuum. Anyone have any ideas?



Thanks in advance,

__________________
Mike Cougler
New 725 owner

 

[MJCougler]

Vacuum advance for civilian distributor on a stock 1920 carb on an M725 engine

Again, I have a civilian distributor on a military engine. I have a newly rebuilt 1-barrel Holly 1920 carburetor. Newer 1920 carbs have a vacuum port to tap off the vacuum for the vacuum advance. See link below:

http://www.carbkitsource.com/tech/Holley/H1920/H1920.pdf

Is it possible for a non carburetor engineer like myself to drill, tap or add a vacuum port to a non-ported military 1920 carb and have it work correctly? Anyone have any ideas?

Thanks in advance,

 

[kvflyer]

Mike,

I am not ignoring your request but I don't have an answer. Did the Holley 1920 from a Chrysler product slant six have that port? Maybe you could snag one of them. I guess they are getting somewhat scarce now but were certainly plentiful at one time.

 

[mbrosch]

Again, I have a civilian distributor on a military engine. I have a newly rebuilt 1-barrel Holly 1920 carburetor. Newer 1920 carbs have a vacuum port to tap off the vacuum for the vacuum advance. See link below:http://www.carbkitsource.com/tech/Holley/H1920/H1920.pdfIs it possible for a non carburetor engineer like myself to drill, tap or add a vacuum port to a non-ported military 1920 carb and have it work correctly? Anyone have any ideas? Thanks in advance,

So the nature of your issue is that you want to find a proper tap to operate your vacuum advance, and you believe this could be accomplished by drilling the carb? If you ask this question I think the answer is; Leave it alone. But more importantly, what I wrong with where it's sampling now? What is the engine doing that make you think it's related to where the advance gets it's vacuum?

 

[bcowanwheels]

As close to the carb base as possible, you might have to drill and tap the intake manifild.

 

[m16ty]

I've got a civilian distributor on m715. I'll look and see where my advance is tied in.

 

[donnerwetter58]

As close to the carb base as possible, you might have to drill and tap the intake manifild.

Anywhere below the throttle plates is manifold vacuum. Not where you want a vacuum advance plumbed. You don't want full advance at idle. You don't really want any vacuum advance at idle. Vacuum advances are plumbed to "ported" or venturi vacuum sources above the throttle plates. There is little vacuum at idle and vacuum increases with RPM at these ports.