Fuel/Air screws
06-12-2009, 02:53 PM
#1
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Fuel/Air screws
Question:
I am not getting a response from my fuel/air screws. I can see a difference on the vacumn guage & tune them accordinly that way, but no difference in the way the motor actaully runs. I can screw one in totally, no change to idle whatsoever. Is that normal?
Set up: Quick Fuel 950 Hp 76 primary/ 80something in secondaries blocked PV w/jet extensions. No vac advance, or other needed vacumn sorces other than guage. Secondary idle adjustment on carb is only used little.
Checked these things: no vac leaks, PV valve is good & 2.5 inches below idle vac, primary jets seem good @76 (tried 78 & they were too fat). Good seal on each screw, floats seem fine looking at the windows, needle & seat seem to be working fine... etc... what I am I doing wrong? Thanks, Scooter
I am not getting a response from my fuel/air screws. I can see a difference on the vacumn guage & tune them accordinly that way, but no difference in the way the motor actaully runs. I can screw one in totally, no change to idle whatsoever. Is that normal?
Set up: Quick Fuel 950 Hp 76 primary/ 80something in secondaries blocked PV w/jet extensions. No vac advance, or other needed vacumn sorces other than guage. Secondary idle adjustment on carb is only used little.
Checked these things: no vac leaks, PV valve is good & 2.5 inches below idle vac, primary jets seem good @76 (tried 78 & they were too fat). Good seal on each screw, floats seem fine looking at the windows, needle & seat seem to be working fine... etc... what I am I doing wrong? Thanks, Scooter
06-12-2009, 03:09 PM
#2
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Normally when you get no response to turning the screws that means you have the idle SPEED screw turned in far enough that you are exposing too much of the transfer slot in the base plate causing you to pull from the main circuit rather than the idle circuit. Slow the idle down if you can and adjust it and I bet you will see a difference. If it won't run with it backed that far down you may need to drill holes in the throttle blades or flip the carb over and open the secondary blades a small amount with the little screw on bottom
06-12-2009, 03:24 PM
#3
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Tod: good point... I did not even think of that!! It has a pretty lofty cam & likes a high idle... so I do most of the idle adjustment on the primary idle & a little on the secondary idle. I have never even tried that idea so i will see what happens. Thanks!!
06-24-2009, 02:27 PM
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DParker....
I just saw you asked me this question & I forgot I posted this thread. This is a drag car that I am de-tuning for street/strip. It will see the street far more than Woodburn. I am finding that this is a challenging thing to do. The fuel system has been a challenge for street purpose....
I just saw you asked me this question & I forgot I posted this thread. This is a drag car that I am de-tuning for street/strip. It will see the street far more than Woodburn. I am finding that this is a challenging thing to do. The fuel system has been a challenge for street purpose....
06-26-2009, 03:20 PM
#7
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d/aprker:
It could be I am just paranoid... It is not fouling plugs or anything. They are black though. It likes about 1200RPM or a little higher, although my tach just died. What i am trying to do is adjust f/a screws to best potential via vacumn @idle. My goal is best f/a mixture I can get w/o potential ring wash... simply put, micro tuning carb best I can for street use (like being at the cruses) where I am using more of the low/mid range instead of WOT. Some of this is like "your cake & eat it too" when you cannot really have a race car be a street car I guess. Scooter
It could be I am just paranoid... It is not fouling plugs or anything. They are black though. It likes about 1200RPM or a little higher, although my tach just died. What i am trying to do is adjust f/a screws to best potential via vacumn @idle. My goal is best f/a mixture I can get w/o potential ring wash... simply put, micro tuning carb best I can for street use (like being at the cruses) where I am using more of the low/mid range instead of WOT. Some of this is like "your cake & eat it too" when you cannot really have a race car be a street car I guess. Scooter
06-26-2009, 06:37 PM
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Originally Posted by Rigsby
d/aprker:
It could be I am just paranoid... It is not fouling plugs or anything. They are black though. It likes about 1200RPM or a little higher, although my tach just died. What i am trying to do is adjust f/a screws to best potential via vacumn @idle. My goal is best f/a mixture I can get w/o potential ring wash... simply put, micro tuning carb best I can for street use (like being at the cruses) where I am using more of the low/mid range instead of WOT. Some of this is like "your cake & eat it too" when you cannot really have a race car be a street car I guess. Scooter
It could be I am just paranoid... It is not fouling plugs or anything. They are black though. It likes about 1200RPM or a little higher, although my tach just died. What i am trying to do is adjust f/a screws to best potential via vacumn @idle. My goal is best f/a mixture I can get w/o potential ring wash... simply put, micro tuning carb best I can for street use (like being at the cruses) where I am using more of the low/mid range instead of WOT. Some of this is like "your cake & eat it too" when you cannot really have a race car be a street car I guess. Scooter
I don't know if I can explain this very well but I'll try. If you lean your idle screws and air bleeds your idle rpm will go up, then your intermediates will start to add fuel. If you richen your carb up at idle it will slow the idle. My advice would be to be alittle rich at idle, keeps engine cooler and more responsive, and lean your mains out some I would try 72's in the primaries and leave the 80's in the rear. You'll just have to run the rrrs up every so often to keep the plugs from getting to black. That way you might be able to get the idle down to 1000 to 1100rpms. Let me know what you do. take care Scooter....
06-27-2009, 03:05 PM
#9
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Duely noted d/parker.
I never thought about going down that far on the primaries at 72. I certianly could try for sure. At any rate, what you say makes sense for the lesser of the two evils... being it is not really a good street engine. I will be on it soon & let you know the outcome... I may need more advice too. Thanks budyy!! Scooter
I never thought about going down that far on the primaries at 72. I certianly could try for sure. At any rate, what you say makes sense for the lesser of the two evils... being it is not really a good street engine. I will be on it soon & let you know the outcome... I may need more advice too. Thanks budyy!! Scooter
06-28-2009, 07:13 AM
#10
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Originally Posted by Rigsby
Duely noted d/parker.
I never thought about going down that far on the primaries at 72. I certianly could try for sure. At any rate, what you say makes sense for the lesser of the two evils... being it is not really a good street engine. I will be on it soon & let you know the outcome... I may need more advice too. Thanks budyy!! Scooter
I never thought about going down that far on the primaries at 72. I certianly could try for sure. At any rate, what you say makes sense for the lesser of the two evils... being it is not really a good street engine. I will be on it soon & let you know the outcome... I may need more advice too. Thanks budyy!! Scooter
