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1931 LaSalle V-8 Coupe - The Continuing Saga of Vapor Lock - Maybe????

Started by MHASSEL345, June 25, 2021, 05:55:04 PM

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MHASSEL345

I've been following numerous posts regarding vapor lock.  My car has a vacuum tank.  Everything from the vacuum tank back has been reworked (incl. the vacuum tank...bench tested for vacuum).  The car starts and idles beautifully, but when it hits operating temperature, it stalls out and won't restart until it cools.  I have not touched the carburetor (quite frankly it scares me and I don't want to touch it until it is the last resort after I've tried everything else).  I have changed out the coil to a brand new NAPA Six Volt as was recommended to me by a fellow Cadillac person.  I am going to insulate the fuel line running from the vacuum tank to the carburetor (seeing a braided fiberglass coated insulation cover devised for this purpose in the marketplace).  I am also going to use 91 Octane Ethanol free fuel (essentially farm gasoline) to see what happens there.  Any other thoughts on what I should be looking at?  I have not changed to condenser in the distributor...figured that would be all or none.

Thanks!   

wheikkila

I have a question and a thought. so you run it at your house till it warms up and stops running? If so, once it dies could you connect a external tank and fuel pump to the intake line to the carb. Just to see if it will start back up. Or if you know how long it will take you can just hook up the external tank to start with. This would hopefully let you know if it was a fuel or spark issue.
Thanks Wayne     

Glen

Here is a link to a good description of how a vacuum tank works.  Hooking up a fuel pump to a carb designed for a vacuum tank will cause flooding.   The carb is designed for gravity feed, measured in ounces per square inch. 
https://www.allpar.com/threads/basic-vacuum-tank-repair.229060/
Glen Houlton CLC #727 
CLCMRC benefactor #104

fishnjim

That link looks like a good one to follow. 
May want to consider to put a vacuum gauge in line if there isn't one, so you can see what's going on.   Sounds to me like one of two, the vent is not opening or the vacuum is getting deep and the modern gas is flashing through the vacuum line and flooding the engine or the gas won't flow against the pressure drop starving the engine.
Monitoring the vacuum will help understand what's up.   A lot of these early inventions weren't up to today's standards and most are not familiar with the methods so they're a bit frustrating.   Personally, I won't go into pre-war autos.
Always be on the look out for homemade "repairs" made on cars this old, over time they may not hold up.   During the war things were scarce and people used their ingenuity.   

I had a similar issue come up industrially.  I was off managing other things so they pulled me completely off a smaller project that was coming up.   Some of those engineers thought they could control vacuum with a control valve throttling the vacuum line to the pump.  But vacuum isn't constant, the vacuum pump is.  It'll keep pulling down so long as it's connected.  They were having all sorts of start-up/quality issues.   I and others were called in.   What I found was the vacuum crystallizer would reach a certain point and vacuum would continue to deepen and cause it to auto cascade.   The heat of crystallization provided enough energy to boil the solvent and the cold condensing liquid returning to the crystallizer drops the temperature and pressure further and it goes out of control.   I had them add a small reverse acting vent control valve to let Nitrogen in to the vacuum control system to break the vacuum when it got too deep.   They had in essence one way control when two way was needed, ie no way for the pressure to come back up once below programmed set point.  I identified some other scale-up issues and turned it back over to others and it ended up quite successful once the changes were implemented.   Sometime you just need a little nudge from a different set of eyes.