i have a 750 holley vec. sec. only partially opening rear barrels .i checked by put a hair clip on the rod only moving a 1/8 in. and i have the lightest spring in to. if in anyone has any idea why please help me?

 

you have a holley 3310-2 just like all of the vac-sec carbs the vacuum from the motor opens it at wide-open throttle with a load on it.it is openning when you drive it!

 

i did that test at the dragstrip made a pass and check it to see it moved.

 

It'll open as far as the engine can use.

But, that doesn't sound like much. How may RPMs were you turning? Make sure there isn't anything binding or anything wrong with the secondary diaphragm.

 

6000 rpm and i changed the diaphragm three months ago and a new cork thing. my motor should able to take more than that dont u think? its running 13.4 on a lil bigger than a two barrel.

 

By the cork thing I assume you mean the gasket for the vacuum passage between the diaphragm and body.

Make sure all of the passages are open and there aren't any leaks along the way.

 

Welcome to the world of Holley VS carbs. Getting the secondaries fully open ain't easy. Usually they won't open fully- there will often be a smidge of angle left on the secondaries. I think that the vacuum diaphragm isn't capable of full opening on some carbs (runs out of travel). You're going to have to do some investigation to see what the limiting factor is.

The reason you're seeing this is that you're actually CHECKING what most people ASSUME is happening.

I found the same thing on a few Holley VS carbs. Some were emissions-style carbs which use a slightly different VS system which can't possibly get the secondaries wide open.