Quote:
Originally Posted by RET_COP
Be careful about putting a low number PV in without checking your total driving habits with a vacuum gauge hooked up. This could lead to a LEAN condition at higher RPMs while letting off on the throttle and getting back into it.
I had 9"Hg at idle and thought I needed a low PV. I assumed that when I opened the throttle the Vacuum would drop from 9"Hg and also my cruise vacuum would be low. I was dead wrong. I discovered different when I hooked up a vacuum gauge. I also found out that my BG 650 carb is a little on the small side for my 355 and it tends to create more of a vacuum (across the board) during driving.
From idle on light acceleration the vacuum went higher.
I cruise between 8 and 11 inches depending on load conditions ( headwind, hill)
When I got into the throttle vacuum dropped but not as fast as I thought.
So I ended up leaving the 6.5 PV in as it was closed during cruise condition and opened when I needed the fuel without the possibility of a lean condition.
I think there are too many variables to make off the cuff decisions and assumptions. ( carburation, cubic inches, car weight, driving habits, CAM, jets etc.)
Try it on your combination you may be surprised
Lou
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you are right on. I checked my driving with a vacuum gauge hooked up and found that my vacuum varies from 11 to 17 inches of Hg in normal driving. Off the line easy, it drops to about 5. 3/4 throttle drops to about 2 and WOT drops tp 0 for a second and then works it's way up. a 4.5 may have been okay for me , but a 6.5 seemed a little high for my case.
but I still have that funny cruise I am chasing.... i'm looking into the distributor that I now broke....