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Wow this ain't nothing new, I can't believe you guys never had a problem trying to set the idle with an open PV, even worse if it's right at the point where it will open and close all the time, when the PV is open it's dumping fuel in the motor and the idle screws don't do squat, you can close the idle circuit and it'll still run from the fuel being dumped in by the PV!.....
The way I understand these things, the idle circuit is fed from the main well (unless you are dealing with a "divorced" idle circuit in which it has it's own feed passage in the bowl) but is independant from the main circuit having it's own jet (Idle feed restriction) and it's own bleed circuit (adjusted by the idle air bleed orifice).
How does something in the main circuit affect the idle circuit (unless the main circuit is being activated from improper carb adjustment)???
The only way the fuel from a power valve can get into the engine while it is idling is if the valve is ruptured (leaking down through the power valve referance port) or through a booster (because the throttle blades are open too far from improper carb adjustment/set-up or incorrect float height setting).
What are the other way's you are describing??
Last edited by Warp Speed; 03-11-2008 at 04:23 PM.
Just for another opinion. I also have tuned 4150's and 4500's for more years than I will admit.... (the early 70's)
The incorrect power valve for the amount of vacuum will make the engine run rich at idle. We proved this with a Motec digital A/F meter and wide band UEGO O2 sensor. It had the same results on a boost referenced 4150 on a turbo motor and a normally aspirated engine. I actually did this on a bet. We could change the A/F ratio as much as from 13.8 to 12.8 and more depending on the engine. We put a pv plug in and set the A/F at 13.8, then put in a pv with a HIGHER number than the vacuum reading and the A/F went to high 12's, removed the pv and put in a pv with a number LOWER than the vacuum reading and the A/F went back to 13.8.
We have also tuned many times in the water to check the vacuum reading under load at idle and found the same results.
Just my .02
B & D Marine Performance
El Monte, Ca.
I really have a hard time accepting this> That would inticate that EVERY time you set up or down you would have to reset you idle, And i HAVE never ever had to do that. Never! A power valve is nothing more than a pressure (negitive) sensitive valve that lets fuel enter the main well BEHIND the main jet thru a predetermined orfice that in the metering block installed at the factoru (unless it is removable as in B.G's etc.) I f the factory installed jet for the PV is roughly 6 jet sizes and I plug it your telling me I am going to have to reset my idle aiir adjustmment? Is that some how MAGICALLY defferant than just going down 6 jets and leave the PV in? Please explain how this is?
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i remember the thread well on HB. If you look at the path of the fuel through the PV, you can see there's no way it should have any effect on idle. It's physically impossible. I've never seen it happen, purely due to the PV. My guess is that when tests are performed that indicate such an effect, there's other things changing besides the PV. If you could mechanically open and then close a PV while the engine was running, with a properly adjusted carb, and nothing else changed, there should be no difference in idle mixture. If there is, then something else is changing as well. It's really a very simple system. If someone can explain how the fuel is getting through the PV enrichment system at idle in a manner that effects idle, I'm listening. "I don't know, it just does" won't cut it, either.
If God is your co-pilot, change seats!
Acts 2:38, the perfect answer to the perfect question.
I hope we know a little more about carburetors today than we did in the "early 70's"