7042240 Upper Main Bleed Question

[Rhett]

I'm doing a 7042240 from a Buick 455, and I'm at the point where I'm measuring and re-sizing the bleeds, etc...

I"ve found that the upper main air bleed in the body is TINY from the factory - .016! ....Cliff's book says to re-size to .070.... thats alot of drilling! The lower main is already at .070

Before I hog this thing out that much, is there something I'm missing? This is an idle air bypass carb, if that makes a difference.

Thanks, Rhett

[Rhett]

Correction - it's the lower mains - the uppers are in the airhorn.

[Rhett]

uppers are.070

[omaha]

      Not sure, a bit confused.... Sometimes you can get confused easy because of all the airbleeds on all of the various year carbs. Main airbleeds, Idle airbleeds  upper and lower, single main air bleed carbs. Secondary airbleeds air bypass holes. That is why I had to read the book about 6 times just so I could remember. (LOL). I like the pictures in the book.  It really helps.

What did you measure that had the .016 measure, the upper idle bleed?

[Rhett]

Ha! You and me both, brother!

These are the main air bleads - the upper is in the airhorn and is sized at .070 - no problems there. The lower is in the body, in line with the same passage and set back in a round recess in a round brass insert. The thing has the tiniest passage I've ever seen: .016 which is like a #78 bit - we're talking human hair sized.

The carb ran really well with the passage that small, I'm hesitant to drill it out if it's going to significantly change the performance chararistics of the carb....

But until I get a defininative opinion, I'm stuck and can't get this thing back together. 

[Zac Agee]

thats not the main air bleed. i think you looking at the ventura itself. look at pages 32 bottom right picture, page 94, big picture at the bottom shows a pen vise with a bit in the main aire bleed, 112 bottom right corner picture in cliffs book. those are the main air bleeds in the main body and yes those should be tho .070 like it says

[Cliff Ruggles]

I'd leave the MAB's in the casting as is.  They are indirect bleeds.  Don't remember them being that small on that particular carb number.  Some of the 244 carbs had really small MAB's......Cliff

[Rhett]

Zac - thanks for the response and yeah, thats the bleed I'm talking about. 

I started drilling it and got as far as .031 before I decided to get on here and ask some questions. None of my other 240 (66, 67, 73 and 76) carbs have had anything near that small

I wouldnt have though twice about hogging it out except this car was such a tire burner before I touched it.....

[Zac Agee]

yea i understand there.. the MAB's where very confusing when i first got cliffs book so i know what its like. hope it turns out great!

[Rhett]

I always have to get my head straight 2 or 3 times when sizing bleeds - after doing 6-7 carbs I'm about ready for a new copy of the book - mine is dog-eared and filthy, it stays open on the bench the whole time..