Engine troubles

[Harlow]

Alright guys, I'm real close to getting this thing up and going properly. Now my only problems are:

1. When I rev the engine (in park) I noticed that the vacuum drops from about 7 to 5 initially and then jumps up to 10+ (depending on how much I give it). Is it normal for the vacuum to drop and then quickly jump up?

2. When I put the car into gear the RPM drops from 850 to 550-600 and wants to die on me. What going on?

Could these two problems be the result of a vacuum leak?

This is a 383/727 Auto

[Plumcrazy]

A vacuum leak could cause both of those problems.

[Chryco Psycho]

it is normal for the vacuum to drop as the throttle is opened & jump back up as the throttle is either held open or closed , the drop in idle Could be a vacuum problem or just a tight torque converter dragging the engine down

[Back N Black]

At idle you should have around 17 to 20 inches of intake vacuum, unless your running a really big cam, where are you hooking up your vacuum gauge?intake vaccum or ported vaccum?

[Harlow]

I'm hooking the vacuum gauge up between the vacuum advance on the distributor and the vacuum port on the primary metering block. I know its got a pretty big cam for a 383. About 15 years ago the guy I bought it from said he put in a comp cams 292 .510. I'm kinda new to this (17) and I'm not sure what ported or intake vacuum means, if I knew what it meant I could tell you.

[Chryco Psycho]

you are hooked to ported vacuum , above the throttle plates it works so that they is no vacuum at aidle & it increases with rpm , manifold vacuum below the throttle plates works oppostie highest at idle & drops with rpm

[Back N Black]

OK sorry about that, intake vacuum is vacuum below your throttle plates or butterflies whatever you want to call them. So with when your engine is at idle and throttle plates closed thats when you have max intake vacuum 17-20. When you step on the accelerator throttle plate open and vacuum drops off because of the rush of air down in the carb.
Ported vacuum is above the throttle plates and reads zero at idle opposite of intake vacuum.When you step on the gas and open the throttle plates air rushes by these ports causing a vacuum called the venturi effect.
When your hooking up vacuum lines to your carb. it important to know which fitting to attach to because some are ported vacuum and some are intake vacuum.If you have a peek down in the carb. you will see which one are above and below the plates.
So if you checking at the vacuum tree at the back you should be fine.Now for vacuum leaks i use a propane torch,turn on the gas not lit off course and move slowly around the vaccum lines and the base of the carb.if there is a leak the engine will rev. up.
If you don't like the torch spray water and the engine should stumble.Hope this helps, my pointer finger is really tired from typing.

[Back N Black]

I was too slow typing Chryco got to it before i did.