Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (http://www.hotrodders.com/forum/)
-   Engine (http://www.hotrodders.com/forum/engine/)
-   -   Vacuum Question (http://www.hotrodders.com/forum/vacuum-question-224957.html)

pukas84 10-12-2012 11:34 PM

Vacuum Question
 
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.

timothale 10-13-2012 09:01 AM

air leak,
 
Is the Modulator good, sounds like the diaphram is leaking and too much air getting into the intake. A hand pump vacuum tester is handy to have , I have seen guys suck on the tube to see if it holds vacuum, not aa me, if the modulator hose is long enough, run the engine, pinch the hose so it won't leak, pull of the hose put your finger on the end . unkink the hose and you should feel some vacuum in the hose. ,a lot of times a leaking modulator will allow oil to get into the hose..

cobalt327 10-13-2012 11:49 AM

Quote:

Originally Posted by pukas84 (Post 1598619)
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?

bigdog7373 10-13-2012 08:28 PM

Since the engine runs better with it getting more air then you need to check your idle mixture. Sounds like it's rich. What's your timing at?


All times are GMT -6. The time now is 05:01 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.