12.5" Power Valve??
- Thread starter hunt2elk
- Start date
padam
Well-Known Member
You're going to be dumping some fuel in.
Are you sure you're figuring right?
Are you sure you're figuring right?
Just experimenting. On a car that has 16" of cruise vac, I want to see what happens with the valve opening earlier. Power valve doesn't open on the idle circuit.
I think so many guys think it will open on the idle circuit because of the way they have their carb/idle setup. If you have a big cam and have the idle screw turned up past the transition slots in the idle circuit then yes you are drawing on the main circuit of the carb. If you have the correct amount of air going into the carb without opening the throttle blades too far, then you are on the idle circuit and won't be drawing any fuel from the transition/main circuit. Oh and don't mention drilling throttle blades without thinking the carb is junk then to some, even though carb manufacturers send half their carbs with the throttle blades having holes in them.......
I watched a good dyno session on engine masters where Steve the dyno guy moved the power valve up a couple numbers closer to the vacuum number to get it to open a smidge early and take a small area of lean condition out of the cruise to throttle transition. It was cool how you could see that take care of a small area of lean condition right on the air/fuel number before and after.
10.5 is the biggest one they make. If you're into your cruise rpm the jetting will have 'some' effect unless you're going pretty slow, but I get it if you're trying to work the PMJ as lean as possible and have new-car response at the slightest rub of the throttle..tuning that overlapping area where both circuits are contributing is such a balancing act. I have gotten my big Demon to respond very well with a 9.5" and lots of trial/error with PVCR sizes, and adding adjustable transition slot restrictions.
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What are adjustable transition slot restrictions?
It requires drilling and tapping the orfices in the main body that feed the transition slots, so you can then install set screws. You drill the set screws out to whatever size you want the restriction to be. It's not always necessary, but it lets you dial in the mixture better during that part of the carb's operation that gets used the most.
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