Are you looking for a vacuum leak or a positive air pressure leak?

The former may be determined using propane. The engine will rev higher when it sucks propane into a vacuum leak. Connect a fine flexible hose to your propane torch on a low setting.

The latter may be tested with Magician's Smoke in a Can.

http://www.filmtools.com/diffusionin...kaAtk4EALw_wcB

Courtesy of the Tappet Brothers.

Peter Wieck
Melrose Park, PA