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Old 05-22-2012, 12:41 PM
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Idle Fuel Restriction -too big??

My buddy recently purchased a pair of Holley 80576S 750cfm blower carbs for a BBC 496 and they run really, really rich at idle. (no drips/idle set/no leaks/4.5pv) I took the bowls off to see what jets he had in there and took a closer look at the metering blocks. It's a 4-corner idle, so the secondary metering blocks are identical. When I saw the IFR's they looked huge! So I measured them and they were .100....definetly huge!! I then measured the metering block from a plain 750 and they measured at .030. The screw in idle air restrictions measured at .070...which is normal for a 750.

My question is....are the IFR's too large at .100 ???
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Old 05-22-2012, 01:16 PM
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What is the size of the orifice at the green and blue arrow
in this pic.
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Old 05-22-2012, 01:27 PM
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Fbird

Is there a specific size that the green arrow orifice and the blue arrow orifice should be at?? As I don't have the metering plate with me. I need to drive back to his house and disassemble both carbs again. But, I could get you the sizes tommorrow.....
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Old 05-22-2012, 03:16 PM
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Quote:
Originally Posted by tubbedz
Fbird

Is there a specific size that the green arrow orifice and the blue arrow orifice should be at?? As I don't have the metering plate with me. I need to drive back to his house and disassemble both carbs again. But, I could get you the sizes tommorrow.....
Did he buy theses carbs used? Someone may have been running alcohol before which requires larger jets.
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Old 05-22-2012, 03:17 PM
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The idle feed can be restricted at either orifice so the smaller of the two would be your actual IFR.
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Old 05-22-2012, 03:25 PM
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Quote:
Originally Posted by TommyK
The idle feed can be restricted at either orifice so the smaller of the two would be your actual IFR.
Thanks TommyK

That explains alot.....so either the Green orifice or the Blue orifice will have a restriction and the smaller of the two will be size of the fuel restriciton. I got it!!!!
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Old 05-23-2012, 10:48 AM
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Quote:
Originally Posted by F-BIRD'88
What is the size of the orifice at the green and blue arrow
in this pic.
FBird'88

The orifice at the green arrow is .030 and the orifice at the blue arrow is .080
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Old 05-23-2012, 11:39 AM
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Quote:
Originally Posted by tubbedz
FBird'88

The orifice at the green arrow is .030 and the orifice at the blue arrow is .080
The IFR is .030" then. That is the top of idle well.

The IFR can be at either location. I am not that familiar with that specific metering block. The .030" IFR will not be excessive on a blower motor .
Try it as is , first.
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Old 05-23-2012, 12:04 PM
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What are the primary and sec idle and hi speed air bleed sizes in that carb?
what is the main jets? What is the size of the PVCR?
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Old 05-23-2012, 12:36 PM
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Quote:
Originally Posted by F-BIRD'88
What are the primary and sec idle and hi speed air bleed sizes in that carb?
what is the main jets? What is the size of the PVCR?
FBird'88

The idle air bleed is .070 on both the primary and secondary. I did not measure the high speed air bleed. The jets are "out of the box" 76-primary, 87-secondary. I did not measure the PVCR but the pv it came with was 10.5 and we changed it to 3.5. The secondary metering blocks come with pv plugs. It also has 30cc primary and secondary pumps and the squirters are 31 primary and secondary.

The car accelerates like crazy, it is "hell a fun", but at idle it's a little rich. The idle screws are all about a half turn out. We don't mind it being rich at idle we were just curious if we could fine tune the vehicle more.....always tinkering
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Old 05-23-2012, 01:29 PM
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What rpm does it idle at? Could it be pulling fuel out of the main boosters at idle? Have you checked the tslot exposure? What is the initial timing?
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Old 05-23-2012, 01:33 PM
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Define "rich" is rich smelly exhaust?
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Old 05-23-2012, 06:39 PM
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Quote:
Originally Posted by F-BIRD'88
Define "rich" is rich smelly exhaust?
Thanks FBird88 and TommyK for all the information!!

I spoke to him about the situation on the phone, as I was tired of driving to his house to troubleshoot. At this time he's going to leave it as is as he wants to attend a cruise night this weekend. When I have more free time, I'll attempt to diagnose more. All I can say is thank you everyone for your help!!
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