primary rod suffix confusion

[unruhjonny]

I have noticed 'B', 'C', and I believe 'M' & 'V' (going 100% off memory here);

I have taken what appeared to be original carbs which had suffixes on their primary metering rod, but was suprised, because I had though that these suffixes only appeared later (the most recent was a 7029202 which I believe had 'B' rods);

I have previously understood that the suffix denotes a different number/angle step from the thickest to the tip measurement - is this correct?

Do some of these suffixes only apply to 1967-1975 "70" carbs versus "170" carbs?
I have understood that the 1975 was a transitional year, but for the most part '70' vs '170' denoted a different fuel bowl depth - which necessitated a different length rod ('170 use a shorter rod because the floor of the fuel bowl had been raised).

The genisis of this (hopefully not too confusing) post is that I believe I mixed up some of my rods;
I only had a couple '170' rods, but apparently mixed them in with my '70' rods;
I observed that the '170' rods all had the same suffixes - and to date the rods with no suffix were all for '70' carbs.

Questions in point form:

1) do the suffixes apply only to '70' & '170' carbs inclusively? - or can you find (oh lets say a 45B for both '70' & 170' quadrajets?

2) can someone take a moment to spell out which suffixes are used?

I found the secondary metering rod chart in Cliffs book very helpful - I have been going through my stuff lately, in part because I am thinning out my inventory of spare parts, but desire to keep a nice collection of parts for my car, for which I currently have at least two early '70' Pontiac carbs for...

[Ethan1]

I have noticed 'B', 'C', and I believe 'M' & 'V' (going 100% off memory here);

I have taken what appeared to be original carbs which had suffixes on their primary metering rod, but was suprised, because I had though that these suffixes only appeared later (the most recent was a 7029202 which I believe had 'B' rods);

I have previously understood that the suffix denotes a different number/angle step from the thickest to the tip measurement - is this correct?

Do some of these suffixes only apply to 1967-1975 "70" carbs versus "170" carbs?
I have understood that the 1975 was a transitional year, but for the most part '70' vs '170' denoted a different fuel bowl depth - which necessitated a different length rod ('170 use a shorter rod because the floor of the fuel bowl had been raised).

The genisis of this (hopefully not too confusing) post is that I believe I mixed up some of my rods;
I only had a couple '170' rods, but apparently mixed them in with my '70' rods;
I observed that the '170' rods all had the same suffixes - and to date the rods with no suffix were all for '70' carbs.

Questions in point form:

1) do the suffixes apply only to '70' & '170' carbs inclusively? - or can you find (oh lets say a 45B for both '70' & 170' quadrajets?

2) can someone take a moment to spell out which suffixes are used?

I found the secondary metering rod chart in Cliffs book very helpful - I have been going through my stuff lately, in part because I am thinning out my inventory of spare parts, but desire to keep a nice collection of parts for my car, for which I currently have at least two early '70' Pontiac carbs for...

 I am not certain if metering apply for certain years, Jon. Great question! I suppose so after all the changes made in-and-around '75. And your assumption is correct about the suffix denoting single/double taper and size of tip.

1)Answered your first question already kind of. I am not certain if a 49B rod would work in a later unit. To be honest, I don't know why it wouldn't.

2)These are the ones I know of and I am sure there are others, so anyone, please feel free to add to list:

A .026" Single-Taper, B .026" Double- Taper, C .026" Double-Taper, D .050" Double-Taper, E .026" Double-Taper, J .026" Double-Taper, K .026" Double-Taper, M .036" Double-Taper, P .026" Double-Taper, S .026" Double-Taper, T .026" Double-Taper,  and V .026" Double- Taper.

[Cliff Ruggles]

Primary metering rods do NOT interchange between early and late designs.  Early carburetors use longer primary metering rods, the most common are "B" series.

Later carbs (two pairs of MAB's) will use shorter rods, and there are a wide variety, with "K" being very common.  '

Single MAB carbs for the most part used "M" series metering rods which are also shorter but have .036" tips instead of .026".  Some later units used special metering rods, also shorter with .036" tips, like the later Motorhome carburetors......Cliff

[Ethan1]

Primary metering rods do NOT interchange between early and late designs.  Early carburetors use longer primary metering rods, the most common are "B" series......Cliff

 Thanks for the clarification, Cliff.

[unruhjonny]

I never suggested mixing early (70) vs late (170) primary needles...

[Cliff Ruggles]

There are many carburetors starting with 1705 or 1708 that still use the longer primary metering rods, such as all of the Marine units, and 1975 to 1978 Chevy truck carburetors (no CA emissions)......Cliff

[unruhjonny]

/\ now that, I had no idea...

I had understood that the 70 vs 170 numbering system was to denote a raised bottom of the fuel bowl - which necessitated a shorter needle.

Huh.

Thanks for sharing some more of your knowledge Cliff!

[Cliff Ruggles]

As far as what you are most likely to find, "B" series were used in a lot of early units and many of those carburetors will have the early APT system in the baseplate between the mixture screws.

"K" rods are quite common from 1975 to 1980 or so and used in the later style APT units. 

"M" series rods were used in the 1979 and later APT Q-jets with the single main airbleed design.

Of course there are a few exception here and there, most will be Holden, Canadian, Motorhome and Marine applications......Cliff

[unruhjonny]

Thanks Cliff!