4M-Style SMB Truck Carb. Primary Rods...

[firefox3]

What style(or letter) primary metering rods do the mid to late 70's, 4M-style, SMB truck carbs use?

Do they have .036" power tips like the "M" rods used in the later M4-style SMB carbs?

Thanks...

[77cruiser]

Some later ones had K rods with the .026 tip.

[firefox3]

Some later ones had K rods with the .026 tip.

Wouldn't "K" rods be too short for a 4M-style SMB carb.?

[Ethan1]

What style(or letter) primary metering rods do the mid to late 70's, 4M-style, SMB truck carbs use?

Do they have .036" power tips like the "M" rods used in the later M4-style SMB carbs?

Thanks...

 What carb number?

[firefox3]

Carb. number is 17057213.

[Ethan1]

Carb. number is 17057213.

 Don't know if this helps any, but that carb came stock with 40B primary metering rods.

[firefox3]

Ethan, you must be a walking RPD Quadrajet specification manual.

That carb. is definitely a SMAB model with the triangular-shaped air bleed in the air horn.
So it seems as though both the SMAB and DMAB 4M-style carbs. all used either "B" rods or single taper rods with .026" tips.

Thanks...

[Cliff Ruggles]

The 17057213 is an older style divorced choke carburetor, but used the later style single main airbleed set-up.  There will take the early style "B" series metering rods, not the later style "M" series as used by the hot air and electric choke SMAB carburetors.

The early SMAB units are really nice carburetors, and came with very small main jets in them.  Usually 64's, but we've seen a few show up with 63 main jets in them, and they are factory calibrated with "B" series metering rods via the APT system in the baseplate.....Cliff

[firefox3]

So it sounds like they used very small main jets because of less emulsion air and the "B" rods smaller(compared to "M" rods .036" tips) .026" tips.

Thanks for the replies.

[Cliff Ruggles]

I would also mention that the factory calibrations on that particular carburetor varied some, and will NOT be what is found in the "book" if you look them up.

Most had either 63 or 64 main jets, and metering rods ranging from .036" to .040".  They were fine tuned by the factory using the APT system in the baseplate.

Those are excellent carburetors, using the later SMAB set up bit early castings and still divorced choke.....Cliff

[Ethan1]

I would also mention that the factory calibrations on that particular carburetor varied some, and will NOT be what is found in the "book" if you look them up.

Most had either 63 or 64 main jets, and metering rods ranging from .036" to .040".  They were fine tuned by the factory using the APT system in the baseplate.

Those are excellent carburetors, using the later SMAB set up bit early castings and still divorced choke.....Cliff

 Good point, Cliff. Some carburetors were calibrated differently, than what the book states. Agreed 100%.

[Cliff Ruggles]

Yes, I find LOTS of deviations in the jets/metering rods used, especially on the later production units.  The book should be used for "reference" only, at least when it comes to basic tuning/parts selection......Cliff