Ok so I have a 383 with a barry grant 750cfm dp carb, sports claw. The car runs great no problems, but I'm always tuning just for fun. Last year I got out the vacuum gauge and properly set the idle screws and everything worked out great. This year after reading about power valves I thought I would check the vacuum to see what power valve would be correct and the gauge reads no vacuum. Now when I increase the rpm a little I get some vacuum but only a little. I am using the correct port to obtain the manifold vacuum according to the carbs instructions, the front port on the passenger side.
I am running a crane energizer cam, .480/.480" lift 284° advertised duration (228° at .050")

Any thoughts???
Thanks

Maybe I Should just not screw with it and call it good but you know how that goes, always looking to make the car run a little bit better!!

 

where is the port you are testing from

 

I have two small ports on the passenger side of the carb I hooked the vac gauge up to the one towards the front of the car.

 

so are the orts you are using in the middle of the carb or on the base plate of the carb.

 

Yeah sorry, both of these ports are on the baseplate of the carb

 

well darnit it should be intake vacuum.
http://www.barrygrant.com/fromBarryG...n%20Manual.pdf

 

maybe your vacuum gauge is not functioning correctly?

 

You're tapping into the ported one which as you've found out will work when the throttle is cracked open. Use the other port for reading vacuum with a gauge.