Help with vacuum line.

[rcl700]

Can someone help provide me some information on the line that vacuum line from the distributor to the carb on a 1948 deluxe. My car does not have this line. I guess it was pulled off some time long long ago. The carb currently has a plug installed. 

 

What size line should this be and what ends are needed to connect it to the distributor and car? 

My car is completely stock. 

 

I dont have a bender or flaring tool but I can get these items if needed. 

I think harbor freight has them at a relatively low cost. 

[Sam Buchanan]

It is likely the vacuum advance diaphragm on the distributor is defective. The vacuum line was probably removed to eliminate an intake leak.

 

A 1/8” NPT elbow at the carb and a pre-flared brake  line is all that is needed to connect the vacuum advance. But verify the advance unit is working first make sure your line is long enough for a stress relief loop at the distributor.

 

Edited October 15, 2023 by Sam Buchanan

[rcl700]

1 hour ago, Sam Buchanan said:

It is likely the vacuum advance diaphragm on the distributor is defective. The vacuum line was probably removed to eliminate an intake leak.

 

A 1/8” NPT elbow at the carb and a pre-flared brake  line is all that is needed to connect the vacuum advance. But verify the advance unit is working first make sure your line is long enough for a stress relief loop at the distributor.

 

So use 3/16 brake line and fittings? Then adapt down to 1/8"?

Is there 1/8" line? 

 

I'm sorry for my lack of knowledge regarding this stuff. 

[plymouthcranbrook]

You can also use a sturdy rubber line. I have a length of fuel line on my 52 Plymouth and it works fine.  Unless you are looking for the factory stock look.

[Merle Coggins]

I ended up using short pieces of line at the carb and distributor and connected the two with a piece of vacuum hose. If you do that you could purchase a short pre-made piece of brake line and but 2-3 inches off each end. Connect those ends to the vacuum advance and carb fitting, then use vacuum hose to finish the connection. No need to worry about how long to get the brake line, or worry about how, or where, to make the bends. 

 

I would also recommend testing the vacuum advance as someone else said. 

[Sam Buchanan]

22 hours ago, rcl700 said:

So use 3/16 brake line and fittings? Then adapt down to 1/8"?

Is there 1/8" line? 

 

I'm sorry for my lack of knowledge regarding this stuff. 

 

The elbow for the carb has 1/8" NPT threads. I don't recall exact size, Just get a line that has fittings that match the one on the advance unit. As mentioned above rubber vacuum tubing will work, just make sure it is situated so it can't be damaged by the hot cylinder head. But I suspect you have a defective advance unit and that is the reason the port on the carb is plugged.

Edited October 16, 2023 by Sam Buchanan

[Sniper]

In this picture you can see where the hard line for the vacuum advance hooks to the carb on my 51 Plymouth.

 

[Sniper]

In this picture you can see how the hard line is routed across the engine.  I do not have a good picture of the distributor end of the line, sorry

 

[Sam Buchanan]

Photos of the vacuum line in my '48 P15. The elbow at the carb eliminates the need for a sharp bend in the line. Also visible is the line crossing the cylinder head. As a bonus the home-made heat shield for the carb is also shown.

 

 

 

Here is the stress relief loop at the distributor that allows it to rotate to set timing.

 

 

Edited October 15, 2023 by Sam Buchanan

[rcl700]

Thank you Sam and Sniper. These pictures really help. ?

 

As for testing the vacuum advance, how is this best achieved? 

Edited October 15, 2023 by rcl700

[Sam Buchanan]

A rudimentary test just to prove it isn’t totally dead is to hook up one end of a line to it and suck on the other end. If resistance is felt remove the distributor cap and see if the points plate is moving when you apply vacuum. Most likely the diaphragm is blown and it won’t hold a vacuum and move the plate. Another failure mode is the unit being stuck.

[rcl700]

34 minutes ago, Sam Buchanan said:

A rudimentary test just to prove it isn’t totally dead is to hook up one end of a line to it and suck on the other end. If resistance is felt remove the distributor cap and see if the points plate is moving when you apply vacuum. Most likely the diaphragm is blown and it won’t hold a vacuum and move the plate. Another failure mode is the unit being stuck.

Thank you. I guess I'll pucker up and give her a test ?

[Dodgeb4ya]

Std. 3/16" steel brake tube is the factory vacuum advance line size ...

A 3/16" tube nut at each end.