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Jet sizes?

  1. #29
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    Quote Originally Posted by 058 View Post
    Sorry Art, I'm not buying that, if the p/v is open at idle it will not effect idle one iota. If you track the fuel path of the p/v into the pvcr it goes in to the main jet well. The only time a good p/v can effect idle is if the p/v is occilating[sp] in effect pumping fuel into the main circuit. This condition is rare and would be one of the last things I'd look at if I were chasing a rich idle condition. It would be easy to spot as there would be fuel dribbling from the boosters.
    Bob, did I mention "Idle Circuit"??, if the power valve is open at idle it will dump fuel in the motor thru it's own cicuit and make it idle rich, in fact you can just about turn the adjusting screws all the way in and it will still run!.. Didn't we have a about a 10 page discussion on this a while back, LOL!....

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    Quote Originally Posted by GoFastRacer View Post
    Bob, did I mention "Idle Circuit"??, if the power valve is open at idle it will dump fuel in the motor thru it's own cicuit and make it idle rich, in fact you can just about turn the adjusting screws all the way in and it will still run!.. Didn't we have a about a 10 page discussion on this a while back, LOL!....
    Huh???

    I missed this discussion!

  4. #31
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    Quote Originally Posted by GoFastRacer View Post
    Bob, did I mention "Idle Circuit"??, if the power valve is open at idle it will dump fuel in the motor thru it's own cicuit and make it idle rich, in fact you can just about turn the adjusting screws all the way in and it will still run!.. Didn't we have a about a 10 page discussion on this a while back, LOL!....
    Art, we beat this subject like a rented mule and no, you didn't mention "Idle Circuit" but I don't see how a open [good] power valve can make for a rich idle assuming all other things are correct like no cross-channeling or internal leaking. Can you provide a link to the thread where this was discussed? My CRS must be kicking in as I don't remember the gist of the discussion.

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  6. #32
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    Quote Originally Posted by GoFastRacer View Post
    Bob, did I mention "Idle Circuit"??, if the power valve is open at idle it will dump fuel in the motor thru it's own cicuit and make it idle rich, in fact you can just about turn the adjusting screws all the way in and it will still run!.. Didn't we have a about a 10 page discussion on this a while back, LOL!....
    Interesting.. This is exactly what I am experiencing. It keeps picking up rpm the more I tighten the idle screws (all 4 corners) until they are bottomed out.

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    Quote Originally Posted by GoFastRacer View Post
    Bob, did I mention "Idle Circuit"??, if the power valve is open at idle it will dump fuel in the motor thru it's own cicuit and make it idle rich, in fact you can just about turn the adjusting screws all the way in and it will still run!.. Didn't we have a about a 10 page discussion on this a while back, LOL!....
    Care to ellaborate???
    I spent 10 years tuning and modifying 4150 carbs at a proffesional level and this is a new one to me??

    Always open to learning something new, or maybe just refreshing my memory that isn't what it used to be!!

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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!.....

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    Quote Originally Posted by 058 View Post
    Art, we beat this subject like a rented mule and no, you didn't mention "Idle Circuit" but I don't see how a open [good] power valve can make for a rich idle assuming all other things are correct like no cross-channeling or internal leaking. Can you provide a link to the thread where this was discussed? My CRS must be kicking in as I don't remember the gist of the discussion.
    Yes we did beat it up, but that was in HB and that's all gone now, think it was back about when we beat up the prop nut subject!..

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    Quote Originally Posted by GoFastRacer View Post
    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!.....
    I need you to explain this to me because I'm still not catching your drift.

    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.

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    Quote Originally Posted by GoFastRacer View Post
    Yes we did beat it up, but that was in HB and that's all gone now, think it was back about when we beat up the prop nut subject!..
    WOW....that DOES go way back... and you expect me to remember that far back? CRS ya know. And yes, "THE" prop nut thread. Back to topic, The only way a open p/v can effect idle and its quality is if the p/v is occilating or pumping fuel into the main jet well. If it stays open or closed nothing will flow without enough airflow to initiate "pull" thru the boosters/main jet well. If the p/v is occilating [pumping] then it could be seen dripping at the boosters at idle.

  12. #38
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    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.
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  13. #39
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    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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  14. #40
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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.
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    Quote Originally Posted by BDMarine View Post
    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
    Not sure on a "boost referenced" 4150, but I would bet if you figured out why it was changing the AFR it would run better....because it won't change it unless something else is off...........or the main jet is smaller than the idle feed restriction


    I hope we know a little more about carburetors today than we did in the "early 70's"

  16. #42
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    Quote Originally Posted by Warp Speed View Post

    I hope we know a little more about carburetors today than we did in the "early 70's"
    Why? They haven't changed much since the early 20s. Maybe thats the problem

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