can't pull vacuum

[dmstang]

Track rules states engine must pull 12" vacuum at 900 rpm. This is a new engine with new schneider cam, The guy (Jerry) who sold me the cam confirmed that it will pull that much.

What will cause low vacuum and how can I bring it up to 12"

I've checked for leaks and can't seem to find any, played with timing and didn't help at all.

Any suggests what to do? Thanks.

[84Dave]

How much vacuum does it pull on your gauge? Have you tried another gauge to be certain yours is OK? What engine is it? V-8 or 4-cylinder? Single carb? Manifold used? Where are you monitoring the vacuum? Is the vacuum the same, whether the engine is cold or hot? No cylinder miss? Cranking compression? Valve lash OK and not hanging a valve open? How did you degree the cam to the proper installed position? -Dave-

[PitManArm]

I always use a vacuum gauge to adjust my idle mixture. That might be a good place to start. Adjust each barrell a half a turn at a time until you have the highest vacuum reading you can get.

[little302]

Like pitman said. Adjust the idle mixture screws and acheive the highest amount of vacuum. This will not only take care of the issue assuming all else is correct, but will give you excellent throttle response. Many people in non vacuum classes overlook this major tuning advantage, and think there is something"wrong" with the carb, when all it needs is an adjustment. They laugh when I pull out the vacuum guage, and start to tune it. Until they see the results...;)