Holley idle feed restrictors

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c1500sbc
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Holley idle feed restrictors

Post by c1500sbc »

I just modified a Street avenger 750 vacuum secondary to accept both changeable air bleeds and idle feed restrictors. Air bleeds are pretty close to stock configuration. I stupidly didn’t measure the idle feed restrictors before I drilled them out. I relocated them to the top of the metering block as well. I drilled them with a .8mm (.031) drill bit on the the primary and secondary metering blocks. It’s waaaay to lean at idle. Won’t even run with the idle mixture screws three turns out.

Anyone know what the stock size is? Or a good place to start?
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Re: Holley idle feed restrictors

Post by ClassAct »

My question is why did you move them up? They should be down not up. You also have to calculate what the idle air bleed is and deal with that. With a .031 idle feed restrictor you’re going to want to be at about and .072 or so Idol feed restrictor.
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Re: Holley idle feed restrictors

Post by c1500sbc »

ClassAct wrote: Wed Sep 08, 2021 10:47 pm My question is why did you move them up? They should be down not up. You also have to calculate what the idle air bleed is and deal with that. With a .031 idle feed restrictor you’re going to want to be at about and .072 or so Idol feed restrictor.
Just following the couple of online guides I saw for modifying the metering blocks. Plus, all the aftermarket ones have them at the top? By top I mean the “outlet” to the channel leading to the idle and transition circuit.

Did you mean a .072 main jet or idle air bleed?
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Re: Holley idle feed restrictors

Post by 1972ho »

He more than likely meant 072 idle air bleeds and the restriction should be around.035 in the lower section to keep it flooded with fuel.And does your butterfly’s have and bypass air.
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Re: Holley idle feed restrictors

Post by c1500sbc »

1972ho wrote: Wed Sep 08, 2021 11:26 pm He more than likely meant 072 idle air bleeds and the restriction should be around.035 in the lower section to keep it flooded with fuel.And does your butterfly’s have and bypass air.
I’m still newish to carbs. Read a few books but just starting playing around with air bleeds and idle feed restrictors. If I recall the idle air bleeds are currently .067. Why would adding more air at idle cure a lean condition? Also, why do the proform and quick fuel metering blocks have the idle restrictors at the top? The original spot, where the presses in restrictors are, is just a blank hole and they move the screw in bleed to the top. Same as I did mine?

No bypass air in the butterfly valves. The four corner idle adjustment has worked great. Prior to the change the idle adjustment screws were 3/4 a turn out for best vacuum and the transition slot was within spec.
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Re: Holley idle feed restrictors

Post by 1972ho »

https://www.tapatalk.com/groups/racingf ... olley-f25/ If you check out this sight there is info there by the moderator about the location of the idle restriction.And yes going higher in size on the idle bleed will cause it to be leaner.But sometimes at idle the exhaust can have reversion and making the O2 read a higher than it actually is.My QF 780vs runs lean at idle and no matter how large I have made the idle fuel restriction it’s still lean.
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Re: Holley idle feed restrictors

Post by Walter R. Malik »

c1500sbc wrote: Wed Sep 08, 2021 10:59 pm
ClassAct wrote: Wed Sep 08, 2021 10:47 pm My question is why did you move them up? They should be down not up. You also have to calculate what the idle air bleed is and deal with that. With a .031 idle feed restrictor you’re going to want to be at about and .072 or so Idol feed restrictor.
Just following the couple of online guides I saw for modifying the metering blocks. Plus, all the aftermarket ones have them at the top? By top I mean the “outlet” to the channel leading to the idle and transition circuit.

Did you mean a .072 main jet or idle air bleed?
They are at the top mostly because they are easier to change ... it will run better with that idle feed restriction below the fuel level.
The EPA emissions are a little bit higher at "start-up" in the lower placement and that is usually why the carburetor manufactures moved them.
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Re: Holley idle feed restrictors

Post by 1980RS »

Hope you added the sec pick up tube on that Avenger,, or all you will be running on the primary side only.
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Re: Holley idle feed restrictors

Post by c1500sbc »

1980RS wrote: Thu Sep 09, 2021 1:30 pm Hope you added the sec pick up tube on that Avenger,, or all you will be running on the primary side only.
I did. You are referring to adding the brass tube from the primaries to the secondary vacuum pod, right?


From the research i've done, the current IFR and IAB sizes aren't very far off from some of the stock set ups. I started small so I could enlarge as needed. Maybe I have a restriction in the metering blocks. I'm going to take them back out and blow through them to check.
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Re: Holley idle feed restrictors

Post by 1980RS »

c1500sbc wrote: Thu Sep 09, 2021 2:04 pm
1980RS wrote: Thu Sep 09, 2021 1:30 pm Hope you added the sec pick up tube on that Avenger,, or all you will be running on the primary side only.
I did. You are referring to adding the brass tube from the primaries to the secondary vacuum pod, right?


From the research i've done, the current IFR and IAB sizes aren't very far off from some of the stock set ups. I started small so I could enlarge as needed. Maybe I have a restriction in the metering blocks. I'm going to take them back out and blow through them to check.
=D> Yes that's the tube I was talking about, makes those 770's work pretty good.
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Re: Holley idle feed restrictors

Post by levisnteeshirt »

ClassAct wrote: Wed Sep 08, 2021 10:47 pm My question is why did you move them up? They should be down not up. You also have to calculate what the idle air bleed is and deal with that. With a .031 idle feed restrictor you’re going to want to be at about and .072 or so Idol feed restrictor.
Oh boy ,, it depends on what it's used for if it works better at the low spot or high ,, if i left off a trans brake leave it low if you want ,, if you like to play with O2 gauges especially

If you want it to be more responsive , move it to the top ,, i always move them to the top and the throttle response is way better ,, I'd like for some of these clowns that say to never put them at the top to build a carb for circle track ,, a footbrake drag car would like it too ,,

Go to a .035 IFR and a 072 idle bleed , make sure there isn't any vacuum leaks ,, idle mixture screw adjustment that doesn't seem to have any effect could also be a stuck open power valve ,,

How much idle vacuum does it have ?
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Re: Holley idle feed restrictors

Post by levisnteeshirt »

One thing , make sure all of the holes intersect in the idle circuit ,

Take the mixture screws out and shoot carb cleaner through them

Make sure the fuel level is right in the bowls ,, i like the orange cam usually and try a .031 squirter on it
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Re: Holley idle feed restrictors

Post by levisnteeshirt »

One thing , make sure all of the holes intersect in the idle circuit ,

Take the mixture screws out and shoot carb cleaner through them

Make sure the fuel level is right in the bowls ,, i like the orange cam usually and try a .031 squirter on it

Measure the diameter of the hole the mixture screws seat into when all the way in too
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Re: Holley idle feed restrictors

Post by BradH »

levisnteeshirt wrote: Sun Sep 19, 2021 2:03 am ...
If you want it to be more responsive , move it to the top ,, i always move them to the top and the throttle response is way better ,, I'd like for some of these clowns that say to never put them at the top to build a carb for circle track ,, a footbrake drag car would like it too ,,
...
I'll be interested in trying it in both positions to see if I notice any difference in a street/strip application.
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