ported vacume????

[nickdavis]

what is ported vacume

[Rev]

There are two sources for vacuum. One is sourced from below the butterflies of the carb. That's called manifold vacuum and that's the one you see at idle caused by the intake suction from the pistons going down on the intake stroke with the butterflies nearly closed.. That vacuum falls to near zero as you open the butterflies to WOT. That vacuum is also what draws the gas in through the idle/transition circuit and it also operates the power valve when vacuum falls to 3-6 in./HG.

Ported vacuum is the vacuum caused by the ventouri in the the carb bore and is added to by the booster ventouri. That vacuum is at about zero at idle because there is very little air flowing through those ventouri. As more air goes down through the ventouri, this vacuum inceases. This is the vacuum that actually sucks the gas in through the main jets and sprays it right into the booster ventouri and down through those butterflies as you open those butterflies more. That allows more air through the ventouri and therefore more gas making more power. This ventouri vacuum is also what makes the secondareis open up on a vacuum secondary carb. This makes the secondary butterflies open only on an as needed basis.

Hope this explains the difference in manifold and ventouri (ported) vacuum and how they each function in an engine.

Rev

[nickdavis]

yes it does thank you. it seems that ported seems to be better

[Rev]

Originally Posted by nickdavis

yes it does thank you. it seems that ported seems to be better

Better for what? You have to have both at the appropriate times for the carb to work.

Rev

[nickdavis]

im sorry i must have read it wrong. i looked at my carb. it has a vacume line coming of the distibutor that hooks into the side of the carb. then theres one that hooks up to the side of the carb on the back end that runs down the side of the engine to the looks like the exchaust manifold. it was sounding like that if you hooked the line that went to the side of the carb from the distributor that it would operate better.

[Rev]

The distributor needs ported vacuum so that it advances the timing when you give it the gas from lower rpm before the mechanical timing advance advance has a chance to kick in. The manifold vacuum line that you mention goes down to the vacuum modulator on the passenger side of the automatic transmission. That controls the part throttle shifts in the transmission either upshifts or down shifts.

There is a metal line on some cars from the automatic choke that goes down to the exhaust manifold to provide heat to operate the automatic choke, but it's not a vacuum line.

Rev

[nickdavis]

ok so if i only have two tubes is that bad thing or is that ok?

[Rev]

Should be OK. One ported vacuum line for the distributor advance and one manifold vacuum line for the vacuum modulator on the transmission.

Rev