Expert: Matt Lyons - 3/17/2009

Question
QUESTION: I don't know if you remember talking to me yesterday about the 750 holley, on the 383 stroker with .470/.480 lift cam. You needed the reading to tell me what power valve I needed to get for it, but I did get a vacuum reading in gear today. It was around 8 lbs. The reason I say around is because today I had trouble with it idling. It would idle high, then drop down, then go back up and then back down. Not for sure why it did that, but while it was idling high enough to get a reading, is when I read 8 while it was in gear. With it out of gear it was reading 12 lbs. Did I do something wrong yesterday to get it to idle high and low like that? Thanks again for all the help.
Ron

ANSWER: Of course I remember you! The reason the idle is "hunting" is because you need to open the idle mixture screws some more. 8" in gear means you will probably need a 5.5" power valve. When you do this you will need a bowl gasket and metering block gasket.
I would take the carb off again, thread the secondary idle plate screw in from the top so you can make adjustments without having to remove the carb each time. Replace the power valve and ty it again.
If you need to you can call me at the shop between 9:30am and 4:00pm est. My number is on my website. www.lyonsperformance.com

---------- FOLLOW-UP ----------

QUESTION: Do I need a power valve for the secondaries or is there only one that I need to replace? Thanks for all the help. It means a lot to me and I know once I get it all going right, my son will have fun driving it. Thanks again.

Answer
That carb only has one power valve. Just for info, Holley recommends a vacuum secondary carb for your application. It would give you better throttle response and is a heck of a lot easier to tune.
Their website has a lot of good tuning info and they have a techline you can call.