65silververt

Does anybody know what length secondary diaphragm arm is correct for our holley carbs? Specifically, the 2818? I need to order a new one, but i am not around my car where i can measure currently. There are 3 different arm lengths in the parts catalog.

Thanks for the help!

Vetterodder

I don't know about length but as I recall the stock spring was the silver one. You should be able to find an assortment locally or through Summit or Jegs. Moroso, Holley, Mr Gasket and others market them and they have several weights for faster or slower opening.

65silververt

I have plenty of springs. However, if the arm is too long, the secondaries will never open fully regardless of what spring is installed. So, beware when buying a diaphragm at the local parts store. There are 3 different lengths that i am aware of.
And actually, the stock spring for a 2818-1 is the purple spring.

Vetterodder

The length doesn't determine the opening rate, the spring tension does. For example, in those kits I mentioned contain two yellow springs and the longer one has less tension than the shorter one. Which spring is best for a particular application depends on several factors, rear end gearing being a big one. The goal is to match opening rate to the engines power curve, gearing, and weight.

Mike Geary

The Holley 2818 "Trick Kit" 37-1539, provides a secondary diaphragm with a 2 1/4" rod.

65silververt

I dont think you are following me. The secondaries will still open with a diaphragm that has an arm that is too long and at the same rate as the correct diaphragm, but they will not open all of the way due to the arm being too long.
I have a plethora of springs and that is not my concern. Now that i am home, i can measure the diaphragms and the carburetor so that i can order the correct unit. I just thought somebody might know the correct length so that i could go ahead and place my order with summit.

itsonlyairandfuel

Holley part# 135-4. Ron B.