Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Vacuum Question
Thread: Vacuum Question
View Single Post
  #3 (permalink)  
Old 10-13-2012, 11:49 AM
cobalt327's Avatar
cobalt327 cobalt327 is offline
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by pukas84 View Post
I have a small block Chevy with a demon carb. I Have the vacuum tank hose, trans modulator hose and brake booster hose going to a connector screwed into the back of the manifold. Idle is a little rough. I was messing with my car yesterday and forgot to plug the modulator hose in and the engine was running smooth. When I plugged the modulator back the idle was rough again. Any suggestions on why this happens? Mahalos.
What is the initial timing set at? What's the cam specs?

Might be pointing to the idle circuit being too rich. The added air from the open modulator fitting leaned it back out and the idle smoothed out. Have you adjusted the idle mixture screws to the highest vacuum/idle speed? Is the curb idle screw adjusted so far in that the idle mixture screws don't do anything (or very little) when the screws are turned in or out?
Reply With Quote