17057253 Rochester question main body air bleeds

[Mr.Pontiac]

On my second carb. Rebuild and found that the air bleeds are so small, I am seeing .028. Your book calls for .070 a huge increase. Why are the air bleeds so small from factory.? Referring on page 32 in your book.

[Cliff Ruggles]

The Oldsmobile carbs from that period used a smaller indirect MAB in the main casting.

If you are rebuilding it for a stock application it should be left at the stock size......

[Mr.Pontiac]

Explain MAB Please

[Kenth]

Smaller Main Air Bleeds equals more fuel thru the circuit.
Most M-style Olds units uses small lower Main Air Bleeds and thicker (leaner) primary rods to match.

[Mr.Pontiac]

Thank you for that great explanation.

[Mr.Pontiac]

I was following Cliffs book, I opened up main air bleeds to .070, I thought I was ok,where do I go to from here? Different rods and jets?

[Cliff Ruggles]

What are you setting the carb up for?  Engine details?

[Mr.Pontiac]

Spare street, strip, spare for my 400 motor, with headers and 410 gears, rpm intake.automatic,670 heads

[Cliff Ruggles]

OK, that's a little better.

400CID
670 heads
headers

Compression ratio?

Cam specs (advertised duration, .050" duration, LSA, ICL)?

[Mr.Pontiac]

10.0 to1 compression, 60919 beast cam,.470 lift, 230duration.

[Mr.Pontiac]

Will be ordering a carb. Kit from you shortly

[Cliff Ruggles]

With a RAIV cam in a 400 build at 10 to 1 compression it's going to like a lot of idle fuel and bypass air.

You'll need to use smaller primary metering rods as well.  Those carbs come with pretty large .049" "K" series rods and 73 jets if memory serves me correctly.

Should have CV secondary rods, those are a good choice for what you are doing...

[Mr.Pontiac]

So I did not hurt carb at all by opening up the air bleeds? Yes I’ll get those rods from you.last time I rebuilt one of these carbs you sent me 74 jets.

[Cliff Ruggles]

Not at all.  I've built hundreds of those carbs and they are among my favorite for late model custom units that I sold here over the years.

Linkage, available vacuum ports, convert easily to electric choke, front fuel inlet, etc.....

[Mr.Pontiac]

Thank you