170- series metering rod suffixes

[cobalt327]

Of the late type 170-series metering rods I have, there are several different suffixes. I have "J", "P" and "M" rods. Above “Schurkey” asked about a “L” rod, I’ve not seen those before.

I see that the J (tapered) and P (stepped) rods have about 0.026" tips and the M rods have about 0.036" tips. I want to say the M rods are tapered even though they do have a step, but it seems the step is well above where a step would normally be if it was part of the metering area, if you follow me.

Is there anything else that you can add?

Again, thank you for your time and for generously sharing your knowledge.

[cobalt327]

I should have added "K" metering rods to those above. They have 0.026" tip, and are stepped. Are these similar to the P rods above?

[cobalt327]

I should have added "K" metering rods to those above. They have 0.026" tip, and are stepped. Are these similar to the P rods above?

I just found a post you made on the K rods:

"The "K" metering rods do not have enough adjustment on the upper section, so with each combination that you used, the control of the part throttle A/F was limited to a range of .005".

We never use "K" series metering rods, as they don't provide enough control via the APT screw to give full control of the part throttle fuel from rich to lean.  With a full tapered metering rod, the APT will provide an adjustment range from the larger section (.044" for example) all the way down to the .026" tip size.....Cliff"

So taking that a step further, it would seem the tapered rods (like J and M rods) are preferred over stepped rods when using APT?

[Schurkey]

My 45L rod:



[Later edit:]  I don't know if this is an ORIGINAL metering rod.   The carb was opened up before I got it--idle mixture screws un-sealed.  MAYBE someone has already played games with the fuel curve.

[429bbf]

my friend is giving me a 17056264 off his 76 pontiac 455 stock to rebld it was made by carter. date code E6. when i get it apart ill see whats in it for jets and rods. it never been off the car his folks bought it new.dean

[cobalt327]

my friend is giving me a 17056264 off his 76 pontiac 455 stock to rebld it was made by carter. date code E6. when i get it apart ill see whats in it for jets and rods. it never been off the car his folks bought it new.dean

I'd be interested in that. Coincidentally, I just took apart a '75 Pontiac carb (7045562) with CA calibrations. It has the aneroid-type APT deal on it and is jetted w/a "670" jet. I'm guessing that is a close tolerance jet, and is basically a 67. This carb didn't have the power piston or metering rods so it will help me to know what your '76 carb had for jets and rods.

[Cliff Ruggles]

So taking that a step further, it would seem the tapered rods (like J and M rods) are preferred over stepped rods when using APT?

"M" metering rods are not full taper, they are "stepped", with a .010" range of adjustment or taper on the upper section.  They also have .036" tips, and were used almost exclusively in the later single main airbleed late model q-jets. 

"J" and "L" rods were not used nearly as often as "K" series metering rods.  I see most of the "J" series rods in 1975 and 76 models, "L" rods show up in some Pontiac carburetors between 1975-1980, most used "K" rods.

In almost all cases we replace the primary metering rods, as they will have a "flat" worn on them from long term use.  Same with the jets, most will be "egg" shaped some from the rods sliding in them for many years.

I get hundreds of thousands of PM's, phone calls and direct emails concerning tuning "issues".  We are going to ask you two questions.

"Have you installed one of our kits to get your carb up to par for modern fuel?"

"Did you install new jets and metering rods during the rebuild?"

If you are are using low quality parts, and old jets/metering rods, it's going to be difficult to help you, as the tuning issues are most likely a fundamental problem with the parts being used.......Cliff

[cobalt327]

I get hundreds of thousands of PM's, phone calls and direct emails concerning tuning "issues".  We are going to ask you two questions.

"Have you installed one of our kits to get your carb up to par for modern fuel?"

"Did you install new jets and metering rods during the rebuild?"

If you are are using low quality parts, and old jets/metering rods, it's going to be difficult to help you, as the tuning issues are most likely a fundamental problem with the parts being used.......Cliff

I positively will continue to use your kits and parts as I've done in the past. And I will also start out w/fresh jets and rods once a preliminary set-up has been decided on.

To clarify, at this stage I'm still gathering information. But coming to a decision on how to best set up a carb (originally from a 4.3L V6) to work on a stock 3.8L V6 has me somewhat outside my comfort zone.

My original plans called for duplicating the OEM 1980 Malibu 229 cid DualJet primary calibrations, as the 2 barrel carb runs good for what it is. But my DualJet is a 2 small main airbleed design and the 4.3L V6 Q-jet I wanted to use has the single main bleed located in the airhorn.  

Regards, Mark