CJS, the idea is to get the IFRs as small as possible (to lean out the transition circuit) without negatively affecting the idle quality and without creating an off-idle lean spot. It is expected that you'll have to adjust the idle mixture screws counter clockwise after this change, so don't sweat that. Good idle quality while still having some adjustment remaining on the screws is the goal. The more you can successfully choke down the idle circuit, the more you'll help the light throttle/high vacuum cruise you're encountering. You might have to slowly sneak up on it. Don't go crazy all at once because you might get it "on the hairy edge of just right" today, and tomorrow's atmospheric conditions won't support it. That's why I said to get close with IFRs beginning with stock size IABs, then you can fine tune with IABs without having to get too far off the reservation.

An open power valve at idle won't affect a thing. Think about it - the PVCR feeds into the main well - the same passage as the main jet. Think of the PVCR as being in parallel with the main jet. If the mains aren't flowing, no fuel from the main jet enters the venturi. The same is true for the PVCRs with an open power valve. Another way to think about it - in any situation where a MJ change will not affect the mixture, neither will an open PV. You should have a vacuum gauge in the car as you drive. If the AFR begins going lean under load at, say, 8" hg, you might want to try a 75 or 80 power valve. This might allow you to go leaner on the MJ if you had previously jetted it up to cover this high load situation. Obviously, this strategy won't work if there is a second situation where you have 8" hg and the main circuit is working, but it isn't lean.

Shout back!

J