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vacuum line

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Anonymous-0

Well-known Member
The vacuum line on my 1936 flathead 6 International stakebed truck is 1/8" copper tube that has a ferrule at each end.I removed this thin tube and the ends are almost sealed shut.They have only a tiny pin hole aperture and it is difficult evn to blow ai thru the line. This cannot be correct. Does anyone know whether i shouls ream these ends out some? Also I think I should replace it with at least 3/16" tube?. thanks
 
(quoted from post at 14:21:55 04/14/14) The vacuum line on my 1936 flathead 6 International stakebed truck is 1/8" copper tube that has a ferrule at each end.I removed this thin tube and the ends are almost sealed shut.They have only a tiny pin hole aperture and it is difficult evn to blow ai thru the line. This cannot be correct. Does anyone know whether i shouls ream these ends out some? Also I think I should replace it with at least 3/16" tube?. thanks
Click to expand...
acuum line supplying what? May have a restriction for a good reason.
 
I assume this is the line to the vacuum advance on the distributor?

If so, it should not be restricted. Sounds like someone made a replacement line with a very dull tubing cutter and did not ream the end of the line.

I would keep the original size, but do ream the ends.
 
"it should not be restricted."

HOW do you know that? Over the years, all sorts of restritors and delay valves were used on vacuum advance setups.

I do NOT claim to know for sure his particular setup is intended to be restricted, but if it in fact IS, it would NOT be unusual!
 
I've seen lots of older carburetors with a restriction built into the vacuum part, I believe some older ones even had brass jets in part of the advance vacuum circuit.

Pretty much a different version of the same thing.

I would suspect the restriction is to help protect the diaphragm from engine backfire, and also to keep the advance from being too active and wearing parts more than necessary.

It needs to slowly advance as vacuum rises as the engine stabilizes under a given load, for maximum power and fuel economy.

On the other need, it DOES need to drop back fairly quickly when the "go pedal" is mashed, to retard timing and prevent spark knock.

In the somewhat modern era, before computer control, the two opposing needs were met by having a tiny orifice to slow advance, and a check valve across the orifice to allow for repaid retard when vacuum drops off.
 
When I am working with Vac. advance on an old car. I try to see if first if my Carbuartor Vacume port is clear.Then I will run a vacume rubber hose to the port and to the dist advance. This is only a test hose to see if it works. If the engine runs better that way I will go to the part store and buy a new metal tube than replace the old one out. Most old metal tube get bent or get some rubber in them when the Vacume advance goes bad. Some time compressed air if blown threw them will clean them out and then they will work better. You can always get a new metal line at your favorite Auto store.
 
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