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BUDA Engine vacuum advance

1918ALF

Registered
Hello all, I have a question for the experts. I have a 1918 American LaFrance fire engine that was re-powered in 1948 with a L525 BUDA Engine. The transplant was done at the BUDA factory in Harvey, Illinois. It has a Delco distributor with a vacuum advance, it has a metal vacuum line that goes from the advance to a fitting on the intake manifold. The engine is completely untouched and it is obvious that the metal vacuum line has been there since the installation of the engine. Anyway, I have been slowly rebuilding all the accessories (starter, generator, magneto) and determined that the vacuum advance was not working. So I sent it off and had it rebuilt. Put it back on and it indeed works, however, here is the problem. The moment the engine starts the advance pulls the distributor to its FULL advance and stays at full advance as long as the engine is running. I am assuming it has always worked that way since thats the way it has been hooked up since its installation. I am used to my old 235 Chevrolet were the advance moves the distributor back and forth depending on the vacuum (throttle position etc). I looked on the carburetor which is an updraft Zenith looking for another place to hook the vacuum line the the distributor so it would move the full range etc. and there is no place to hook the line. Question, is it supposed to just go to full advance when the engine starts? It does have dual ignition (magneto and battery with dual plugs per cylinder) Any help would be most welcome !

Scott In Dallas
 

John Newman Jr.

Subscriber
Age
64
Last Subscription Date
01/10/2019
I am not an ignition expert, but I do believe your advance is working properly. At rest (engine off) the advance is in the retard position for easier starting. Once started the vacuum will pull it to the normal advanced running position. A sudden drop in vacuum - when the throttle is opened quickly - will reduce the vacuum and thereby retard the spark slightly so as to not stall the engine on acceleration.
Is there also a centrifugal advance mechanism in the distributor? This will provide additional advance as the RPM increases.
 

1918ALF

Registered
Thanks for the reply... since the vacuum line is plumbed into the intake manifold some distance from the updraft Zenith, opening the throttle has no effect. It starts in the retarded position (which is correct) and once the engine starts the advance moves the distributor an inch or so to its full travel and thats it... That's what I am confused about. Its either all, or nothing. Does not appear to also have a mechanical advance but I should have checked that.. Thanks :)
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
If the throttle is openned under a heavy load, you will lose manifold vacuum, thus retarding timing. Just openning the throttle with no load allows the engine to accellerate very rapidly, and you won't see the vacuum advance work. Taking a steep hill or long grade is what you need to drop manifold vacuum. Best test is to take a long steep hill, once the engine is warmed up, and see if it pings. If not-advance timing until it does, then back off until pinging stops. Try starting the engine, and see if it kicks back. If it does, retard until smooth starts are possible.
Andrew
 

1918ALF

Registered
Hi Andrew, its starts smoothly..... better than my everyday car! It was just weird to see the distributor move all the way once the engine is started. My old Chevrolet 6 doesn't do that. The old BUDA has loads of torque and has a pretty low red-line so to speak. I think 1200 is about it. I am guessing the Mag is set in the middle of the range and the distributor is obviously retarded for start up and then moves to a further advance than the Mag. Since the RPM range is low I guess it doesn't need to advance that much? What you said about the Vacuum loss on a Load makes since, I should have remembered that!! Would be impossible for me to watch the distributor without removing the hood though. Will take her out for a drive and see what happens :) Thanks for the Reply!

Scott in Dallas
 
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