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Idle Fuel

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1970LS5:
I have an original 7040205 EH carb on a completely stock 454. Cliff installed front shaft bushings and repaired all of the fuel bowl plugs and I installed an HP kit during the rebuild. The engine at idle exhibits all of the symptoms of a vacuum leak but I could find no leaks. After re-reading Cliff's book and searching the forum, I concluded that modifying the idle fuel system was in my future.

Since the car is completely stock, I intend to use the specs found in Chapter 6, page 96. Are these preferable to Recipe 1 under the above conditions? Additionally, if the upper idle air bleeds are found to be .090, is there a correction which can be applied to these measurements. The information in Chapter 6 states that all that a .003 to .004 increase should be applied for high performance applications.

Thanks,
Gene

429bbf:
gene if you read the next 20 sentences right after the .003 to.004 it says you can plug the holes in the main casting with a piece of tig rod and redrill them in the air horn from the bottom side . he also states that this is a lot easier than plugging them off in the main casting and resizing them in the main casting. id start with .050 in the air horn if you choose to go this way. hope i didnt confuse you. dean

1970LS5:
Thanks for your reply.

I did read the next twenty sentences about resizing, but since a correction was listed, I want to see if that applies to all applications. I was trying to avoid the resizing process, if possible, in the interest of time and expense since I don't have access to a single TIG rod to fill the hole. Has anyone used JB weld or Marine Tex for this purpose?
Thanks,
Gene

Cliff Ruggles:
Pretty common to find large upper idle airbleeds in Chevy carburetors made in the 1970's.

They also used pretty large idle tubes in many of those applications.  If your engine lacks enough fuel to the mixture screws, it will take larger idle tubes or less idle air to get it done.

I prefer to restrict those large upper idle airbleeds on those units in lieu of using huge idle tubes in them.

They easily tap for 4-40 brass set screws, which I re-size to apprx .059", then use smaller idle tubes in the casting. 

They can also be left blocked off and upper idle airbleeds drilled in the airhorn instead.  They will need to be apprx .050-.055"......Cliff

1970LS5:
Cliff,
 The original idle tubes that you returned to me after completing the machine work were less than .040". (that is the smallest drill size I have at this time) Just so I understand,  I should leave the current idle tubes in place unmodified and reduce the size of the upper air bleed. Would this action then eliminate the need to modify the remainder of the idle system as per recipe 1 or the specs on page 96?

Thanks again,
 Gene

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