One of the missed tuning adjustments required for a Holley is to check the
vacuum signal at idle the addition of a cam or a significant vacuum leak can
lower idle vacuum and result in the 'power valves' opening. Holley usually
sends 6.5 in. vacuum power valves as installed and they need to be tailored
to the actual vacuum in your car. The idle mixture screws with have an
affect on the volume of air/fuel passing the idle needle but not the ratio
and it could be overly polluted by the power valve opening.
Correction:
1. Check ALL areas for leaks and consider disconnecting the Brake
booster and plug the vacuum line to rule it out as a source of leak (or
fluid burning).
2. Use ether/starting fluid/ brake clean/propane sprayed around the
vacuum hose locations to check for engine speed variance (leaks) while the
engine is running.
3. Measure the vacuum at idle when the engine is warm and the engine is
idling at it's slowest speed with the chock (if there) wide open.
4. Determine the reading and ensure that the power valve is 2.0 in.
lower than the lowest attained reading for vacuum. As an example on my 349 I
read a 6.6 in. reading and had a 6.5 power valve. The result was that I had
poor idle control with the mixture screws and a VERY stinky idle despite
running jetted too lean on the dyno (needed 2 more jet sizes). It was also
very sensitive to idle speed as temperature varied. I put in a 4.5 in. Power
valve and the idle adjustment returned and NO MORE STINKY exhaust.
Best Regards,
Tim Ronak
Business Development Manager
Akzo Nobel Coatings
23961 Via El Rocio
Mission Viejo, CA 92691
Off: (949) 305-5393
Fx: (425) 955-6268
Cell: (949) 289-3357
email: timothy.ronak@akzonobel.com
VM: (800) 234-6747 ext. 2257#
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