Can't get low Idle speed

[drew43a]

I have a Edelbrock dual plan performer intake on my newly rebuilt 340 engine and i had a Holley 700 cfm double pumper carb. that i bought used. Altimatly we could not get the idle speed down below 1000 rpm before it would start to stumble and just die.  And i was told that it really was not the most correct carb to run. So i pulled it off and bought a Edelbrock New style AVS2 650. it seemed to run a little better  and wow so much more room around the Distributor and all around the intake.  BUT still cant seem to get a low idle and  i was told it should be about 700 - 800 rpm.  I was reading the other post about the guys intake and tuning issues he had but not ready to be turning and swapping parts yet. Looking for some input as to a cause.  With the holley we had about 10" of vac at idle(950-1100rpm)  never could get lower then that.  Have not checked new carb.  and yes we have searched high and low for Vacuum leaks  and have not found any.

[Rich G.]

The engine is rebuilt but what cam did you put in? A big cam won't idle low without a lot of modifications. Not much information to go by. Timing?

[Chryco Psycho]

There is a screw for the secondary from under the Holley often the the Holley linkage can interfere with the mainfold lifting the carb slightly , .
IMO the Holley is a far better carb , the dyno proves 40-50 hp loss using Eddy carbs .

[RUNCHARGER]

Either carb should work well on a good 340. What are the camshaft specs?

[cudabob496]

In my big block I have a solid roller, with 254/258 duration at .050 inches. For engine to run smooth at idle,
I have the idle at 1200. A high idle is also good for more cooling and more alternator output, when you are sitting at a stop
light.

[Cuda Cody]

Cam and vacuum it creates will play a HUGE part to do with how the carb functions on the idle circuit.   

[cudabob496]

ya, my vacuum is about 10 inches at idle, and I had to have a canister for my
power brakes to  work. Later, I ditched the power brakes.