I have a 4150 HP series Dp Holley. Its the 600cfm no choke. My question is regarding a certain vacuum line. The vacuum line goes from the distributor to the carb itself. However, there are two slots in which it has been used and I do not know the difference between them. One is in the front of the carb under the primary fuel bowl. The other is on the side of the carb in the lower middle portion. I think its the vacuum advance for the distributor and both "plug ins" seem to work fine but I just have to know exactly what each one does. Anyone have any ideas?

Photos would really help. Some vacuum ports are direct manifold vacuum and others are ported vacuum sources. From just your description alone, I'd say both are manifold vacuum and there won't be any difference between them.

One quick way to tell if either one is ported vacuum: with the engine warmed up and idling, uncap one port at a time. If you feel vacuum on the port with your finger it is manifold vacuum. If you feel very little or no vacuum on your finger, it is probably ported vacuum. Most of the time you want to use manifold vacuum for the vacuum advance system on your distributor.

Alright thanks that makes sense. Ill try to get some pictures in just to be sure about everything.

I have a 750DP with a port on the base plate and one lower down on the side of the carb - they are the same vacuum signal, just different locations - assuming they both have vacuum at idle. If so, pick one and plug the other.

Like RIch says, if one does not have vacuum at idle, that is ported. You can use either, but most street cars tend to favour the manifold source.. although people argue this from time to time. If you use the manifold source, the vacuum will advance your dist at idle, the other will not.

I have a 4150 HP series Dp Holley. Its the 600cfm no choke. My question is regarding a certain vacuum line. The vacuum line goes from the distributor to the carb itself. However, there are two slots in which it has been used and I do not know the difference between them. One is in the front of the carb under the primary fuel bowl. The other is on the side of the carb in the lower middle portion. I think its the vacuum advance for the distributor and both "plug ins" seem to work fine but I just have to know exactly what each one does. Anyone have any ideas?

The vacuum nipple in the base plate is constant manifold vacuum.The nipple in the primary metering block is ported vacuum and requires some throttle angle to expose its source.Route your dizzy vac line to the baseplate.it will allow you to close down the throttle angle at idle..keep you out of the transistion ckt and not foul plugs on the street with a proper tune.