Correct Spring for Vacuum Advance???

[jimy]

I just received a new vacuum advance (diaphragm portion) for my 35 Dodge KC pickup.  As I was installing it, it sure seemed to me the existing spring (from the portion that was on the truck) seems very stiff.  It seems almost as strong as a valve spring.  If I squeeze as hard as I can it only moves 1/4 inch. I have my doubts the engine vacuum will give it any more than a tiny bit of movement if any at all.

 

I've never looked at one of these before so I don't know what to expect.  Any thoughts?

 

Jim

[Spinneyhill]

Have you had the curve checked on a distributor machine?

 

The starting point of the centrifugal advance curve is controlled by the installed length and tension of the spring. How quickly the centrifugal advance comes in is controlled by the spring stiffness. The stiffer the spring, the slower the advance curve.
 

[hwellens]

I think he is talking about the vacuum advance, There are specs on the amount of vacuum pull the provides the amount of advance. I have some of those specs for Delco distributors if you list the model number,

[jimy]

My model # is IGS-4111-1

 

(Perhaps with a few transposed letter I's and number 1's)

[hwellens]

On 11/6/2016 at 9:35 AM, jimy said:

My model # is IGS-4111-1

 

(Perhaps with a few transposed letter I's and number 1's)

Looks like you have an Auto-lite distributor. I have no information on those; just Delco

[Spinneyhill]

It is pretty hard to find the spring specifications. MoToR's Truck and Tractor Repair Manual 1950 says the IGS-4111-1 centrifugal advance should start at 3° @ 400 RPM and full advance is 11° @ 1850 RPM. The vacuum advance starts 2° @ 7-3/8" Hg to full advance 10° @ 17" Hg. The only spring tension given is the breaker arm at 17-20 ounces.

 

Of course this won't help unless you put it on a distributor machine.