Ok, heres the deal. On your carb you have a vacuum line going to your distributer advance. Every post I have read on this board says your ported advance should go to this distributer advance(the one with no vacuum at idle and increasing vacuum as you press the throttle).right Mine was hooked up backwards, I just posted a post on this. I called the guy tonight that built the car to check and see if he set the timing with the vacuum tube on the distributer advance, or with it off, so I would know if my timing is completely out of whack. He said he meant to hook the distributer advance into the full vacuum (the one with all the vacuum at idle and cuts off as you press the gas) He said he hooked it up like this because he built it for racing and if it was hooked up the other way it would not run right. He said the weights would advance the timing. This contradicts everything I have read on the board. Is this guy full of or, is there any way your car can run right like this. This guy works for a chevrolet dealership and builds engines all the time, so I would think he knows what he is talking about, but I wanted to ask your guys opinions, since there are alot people who know this area very well. If it will work like this, can you please explain to me how. I am confused. Thanks, please reply

 

Use the ported source. Using manifold vacuum is a very common mistake..altho I really have no idea why. Race applications use either mechanical only or locked out timing.

 

when you said using manifold vacuum is a very common mistake.... although I really have no idea why. Did you mean you don't know why people make that mistake or you just don't know why he would have hooked it up like that.

 

Back in the "old days", and I'm talking per-1966, full manifold vacuum was the norm (some of those old carbs didn't even have ported vacuum). With the advent of emissions concerns, the practice turned to using ported vacuum to decrease NOx. Carbs have been calibrated in the idle circuits ever since assuming no vacuum advance at idle.

It doesn't really make any difference for "performance", since vacuum drops down at WOT and the vacuum advance goes to zero. Sometimes, you can get an agressively-cam'd engine to idle a little higher using manifold vacuum (your cam doesn't fit in that category). Typically, though, off-idle transition will suffer.

BTW, whether ported or manifold vacuum is being used for the vacuum advance, the line should be removed and plugged when setting the timing.