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Discussion Starter #1
Posted in TOBT....got a 9380 850 annular discharge a guy brought me to go through. Secondary idle air bleed has no restriction. Is this normal? Both idle fuel restrictions are .037.
Pretty sure carbs never been messed with.
 

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Thread the idle jets and bleeds so you can tune it, should have had rear restrictors. They were probably removed in an attempt to lean it out.
 

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Are you sure it isn't the primary side that has no idle air bleed? I have seen them every which way, no IAB pri, no IAB sec, and no IAB in either one, but it is most common with no primary IAB. Nevermind all that, what it is ... it is, and it ain't right. Who knows what they were thinking.

The IJ is larger than it needs for most engines, .033" is usually OK with about .070" IAB. With 4 corner curb idle that will work as a starting point on both P and S. After you drive it some to learn what it wants, then tune the low speed level road with the primary IAB. It is best to not have any secondary T-slot exposed at idle.

The annular boosters have a stronger signal than down-leg so a smaller main jet than the same 850 body casting with down-leg boosters may be necessary. It depends on the engine and intake manifold, but PMJ as small as #74 is not unusual with annular boosters in that 850 body casting (1-9/16" venturi x 1-3/4" throttle bore). PVCR will still need to be determined after main jet is selected for best part-throttle A/F in mid-load vacuum above the PV opening point.
 

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Discussion Starter #4
Are you sure it isn't the primary side that has no idle air bleed? I have seen them every which way, no IAB pri, no IAB sec, and no IAB in either one, but it is most common with no primary IAB. Nevermind all that, what it is ... it is, and it ain't right. Who knows what they were thinking.

The IJ is larger than it needs for most engines, .033" is usually OK with about .070" IAB. With 4 corner curb idle that will work as a starting point on both P and S. After you drive it some to learn what it wants, then tune the low speed level road with the primary IAB. It is best to not have any secondary T-slot exposed at idle.

The annular boosters have a stronger signal than down-leg so a smaller main jet than the same 850 body casting with down-leg boosters may be necessary. It depends on the engine and intake manifold, but PMJ as small as #74 is not unusual with annular boosters in that 850 body casting (1-9/16" venturi x 1-3/4" throttle bore). PVCR will still need to be determined after main jet is selected for best part-throttle A/F in mid-load vacuum above the PV opening point.
Sorry for not getting back... was at work. It is primary without bleeds. Checked afew bleeds when I came home and seems as most aren't even the same. Pv was .063/ .067 ,idle air bleed were different two in sec. side. I'm soaking the metering blocks and will investigate more tomorrow.
 

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Discussion Starter #5 (Edited)
Thread the idle jets and bleeds so you can tune it, should have had rear restrictors. They were probably removed in an attempt to lean it out.
I was going to at least equalize existing bleeds and start as small as I could as they seem different. Pretty much like yeti recommended. Thats close to where I usually start....maybe a couple thou diff. It's not my carb and don't really want to get too involved but it is what it is. Don't know much about the car other than 468bbc......procomp:smt119 heads, mid 600 lift. Just try to get him in the ballpark. Done a lot of 850s just no annular booster and wondered what the difference in jetting would run. Stock was 78/78 with pv. This ones blocked in rear...I'll jet by area of holes added or close.
 

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I think that ^^^ will be rich, plenty rich.

With the old non-HP casting with the primary side made for a choke, the flat vertical sides of the choke horn encroach on the OD of the venturi in such a way as to cause the primary to act as if it is a smaller venturi, the result is this casting with annular or down-leg boosters does not use as large main jet + PVCR area in the primary as the secondary even though the venturis are the same 1-9/16" diameter.

In addition to the increased efficiency of the annular booster, the larger size occupies more area of the venturi than the down-leg and the combined result is the annular booster has stronger metering signal, so the jet + PVCR area is smaller than the same carb with down-leg boosters.
 

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Discussion Starter #8
Thanks for replys. Hard to believe this flows the same as a regular 850, man those boosters seem huge. Realized they pull better signal just didn't understand the missing bleeds. Only other carb I've done with boosters like this were factory Ford carbs off Mustang GT.....believe they were on primary side only. Need to get my grass cut before I mess with this one......rain go away!
 

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Discussion Starter #9
Got this back together and waiting on set screws to use for the bleeds. The holes for the IAB that were missing were to big to tap for anything but 10-32, then head of standard bleed wouldn't clear, so I'm just using brass set screws. Most times I've pulled bleed and just tap for 6-32 and never attempted to go to 10s as the old carbs don't have much boss to drill that big. Wondered if anyone has restricted bleeds at metering block mating surface and if it would work ok? This carb was big enough I only had to use the correct drill for10-32 in my pin vice and clean it by hand.......boy it's close though.
 

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Yeah, bleeds at metering block surface will work. Just a little more work to get at to change. I've HEARD of people doing that in class rules that prohibit adjustable bleed main bodies.... Lol
 
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