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SO I picked up a 73 auto carb (apparently 454) 7043200 carb years back as a "spare" and it's sat on the shelf since then. Doing some pre-winter cleaning and I figure I should do something with it rather than collect dust (or maybe it should collect some more)
(I've had mine apart more times than I care to count and it's made the round trip to Lafayette for a Viking hammer tune so I'm not looking to really replace it)
Without opening it up, what would I look at to see if it's a worn-out or "commercially rebuilt" mess? or if it's worth rebuilding?
From: At my Bar drinking and wrenching in Lafayette Colorado
That's a very nice, original, unmolested carb in great rebuildable condition. Somebody has been into the carb before, but you're not going to find a used 50 year old carb that hasn't been opened up at some point in its life, so you're probably going to find some minor assembly or setup irregularities. The over-hanging gaskets are correct - that's how these carbs were built.
Some things I look at are:
All the hardware is correct, and has the correct plating. Airhorn screws are slotted head screws with black phosphate coating - not phillips or torx screws with silver zinc.
The airhorn and the float bowl have not been sandblasted - they have their original brown-ish chromate conversion coating, and it's not in bad shape.
There is no "blockoff T" jammed down into the bowl vent at the rear edge of the choke tower - commercial carb builders jam a Rochester 2GC accel pump checkball retaining "T" into that hole to prevent idiots from pushing their air cleaner stud through the float.
Colors and plating on the steel parts are correct: The secondary airvalves and the choke plate are plain silver cad - not yellow dichromate. Same on the throttle linkages. There is some minor degradation in the plating from corrosion, but it's original and insignificant. Commercial builders will either sandblast and strip the silver cad (leaving a bare steel surface that is usually severely rusted) or they will zinc plate the parts with a yellow dichromate dip, making the parts bright gold. Carbs with gold colored airvalves and chokes have been hacked.
Fuel inlet threads are in outstanding condition. Many commercial builders will install a steel thread insert in the bowl whether it needs it or not. This carb is in great condition.
The throttle lever is the correct big block throttle lever with the lower part of the lever removed by the factory. Hacked big block carbs often use small block throttle plates (with the small block throttle lever). Further verification of this carb having the correct throttle plate is the size of the idle air bypass holes in the primary throttle bores - only the big block carbs had idle holes this big - the small block carbs have smaller holes. Good indication that this carb is correct and unmolested.
All the choke, fast idle, and choke pulloff parts are correct for the model and year. To determine this, you need to have a good photo reference "library" of carbs. Commercial builders, and many backyard mechanics, will alter the choke system, delete parts, or install choke systems from other years and models. This carb has all the correct parts installed.
The long hose on the choke pulloff is correct, as is the rare "T" vacuum fitting that the hose is connected to. The only thing incorrect is that the hose should be connected on the cross portion of the "T" and not on the straight leg inlet. This "T" fitting is usually cracked or damaged on these carbs (the solder joint in the "T" location is very fragile), so most builders will replace it with a straight fitting. The fact that it's intact indicates the carb has not been treated too harshly. It still has the correct, original choke pulloff with the nipple pointing outwards - these are no longer available, and the replacement pulloffs have the nipple pointing inward. If the pulloff is functional and not leaking, just clean it up and use it - don't discard it or replace it.
The choke shaft and throttle shafts still have indication of the green coating originally installed. Good indication of an original carb that has not gone through a commercial stripping operation.
The 2 rear (long) airhorn screws are not grossly recessed into the airhorn casting, indicating that they have not been over-torqued to distort and bent the casting. The carb is not warped, and the secondary airvalves are not jamming against the casting.
The primary well plugs are unaltered, and nobody has smeared any crap-*** epoxy all over the plugs. Good indication that hacks have not trashed the carb.
Overall, you got yourself a winner - very nice rebuildable carb!
Lars
About the only things you can see from the outside is that the configuration of the throttle plate assembly, the throttle linkage and the body and air horn castings appear correct to the part number stamped on the body casting. If you are Lars, you can do this "by eye"....
From: At my Bar drinking and wrenching in Lafayette Colorado
If you either post or e-mail me a few pictures from each side/corner of the carb I can probably give you a pretty fair assessment. If you post those photos here, I can provide public comment for all to see if there are issues, and explain what to look for. If you prefer to keep it private, just e-mail me.
Lets put it up here for future searches, maybe help someone at some point,
Here's what I see as someone who is just a hack
A couple of the flat screw heads I believe I can see where the screwdriver marked the sides of the slots. Also would think the gaskets wouldn't hang out that far in a stock setup and the rubber hose on the choke pull-off seem long
(Sad part is I believe this is still in better shape than what mine was when I started)
OK Lars, what are all the real warning signs without opening it up, hell maybe we can open it up a step or two and show everyone what to look for / at
M
From: At my Bar drinking and wrenching in Lafayette Colorado
That's a very nice, original, unmolested carb in great rebuildable condition. Somebody has been into the carb before, but you're not going to find a used 50 year old carb that hasn't been opened up at some point in its life, so you're probably going to find some minor assembly or setup irregularities. The over-hanging gaskets are correct - that's how these carbs were built.
Some things I look at are:
All the hardware is correct, and has the correct plating. Airhorn screws are slotted head screws with black phosphate coating - not phillips or torx screws with silver zinc.
The airhorn and the float bowl have not been sandblasted - they have their original brown-ish chromate conversion coating, and it's not in bad shape.
There is no "blockoff T" jammed down into the bowl vent at the rear edge of the choke tower - commercial carb builders jam a Rochester 2GC accel pump checkball retaining "T" into that hole to prevent idiots from pushing their air cleaner stud through the float.
Colors and plating on the steel parts are correct: The secondary airvalves and the choke plate are plain silver cad - not yellow dichromate. Same on the throttle linkages. There is some minor degradation in the plating from corrosion, but it's original and insignificant. Commercial builders will either sandblast and strip the silver cad (leaving a bare steel surface that is usually severely rusted) or they will zinc plate the parts with a yellow dichromate dip, making the parts bright gold. Carbs with gold colored airvalves and chokes have been hacked.
Fuel inlet threads are in outstanding condition. Many commercial builders will install a steel thread insert in the bowl whether it needs it or not. This carb is in great condition.
The throttle lever is the correct big block throttle lever with the lower part of the lever removed by the factory. Hacked big block carbs often use small block throttle plates (with the small block throttle lever). Further verification of this carb having the correct throttle plate is the size of the idle air bypass holes in the primary throttle bores - only the big block carbs had idle holes this big - the small block carbs have smaller holes. Good indication that this carb is correct and unmolested.
All the choke, fast idle, and choke pulloff parts are correct for the model and year. To determine this, you need to have a good photo reference "library" of carbs. Commercial builders, and many backyard mechanics, will alter the choke system, delete parts, or install choke systems from other years and models. This carb has all the correct parts installed.
The long hose on the choke pulloff is correct, as is the rare "T" vacuum fitting that the hose is connected to. The only thing incorrect is that the hose should be connected on the cross portion of the "T" and not on the straight leg inlet. This "T" fitting is usually cracked or damaged on these carbs (the solder joint in the "T" location is very fragile), so most builders will replace it with a straight fitting. The fact that it's intact indicates the carb has not been treated too harshly. It still has the correct, original choke pulloff with the nipple pointing outwards - these are no longer available, and the replacement pulloffs have the nipple pointing inward. If the pulloff is functional and not leaking, just clean it up and use it - don't discard it or replace it.
The choke shaft and throttle shafts still have indication of the green coating originally installed. Good indication of an original carb that has not gone through a commercial stripping operation.
The 2 rear (long) airhorn screws are not grossly recessed into the airhorn casting, indicating that they have not been over-torqued to distort and bent the casting. The carb is not warped, and the secondary airvalves are not jamming against the casting.
The primary well plugs are unaltered, and nobody has smeared any crap-*** epoxy all over the plugs. Good indication that hacks have not trashed the carb.
Overall, you got yourself a winner - very nice rebuildable carb!
Lars
My suggestion would be for the OP to send that carb to Lars for rebuilding and for proper adjustment. Money will be well spent, if Lars was willing to take it on.
WOW, now that's a detailed answer and evaluation
I do have a question, what's with this baffle between the primary and secondary area?
I don't have one on my 72 carb, it that something missing or was it added in the 73?
Is it needed, beneficial, meaningless? What was is supposed to be for?
Thanks
M
From: At my Bar drinking and wrenching in Lafayette Colorado
It's a fuel reversion prevention baffle. When the secondaries are slammed open at high rpm, there is a "plume" of misted fuel that shoots out of the secondary accel nozzles and primary discharge nozzles and up out of the secondaries for a split second. The baffle prevents that fuel plume from being ingested down the primary side, and keeps it mostly directed to be ingested on the secondary side. GM doesn't spend money on installing parts that are not needed, not beneficial, and meaningless. The baffles were used on some carbs as early as 1971, but they are not shown or referenced in any of the Rochester parts bulletins. All of the M4M carbs had the baffle. Not all 4MV carbs had the baffle, and I have not seen them on any pre-'70 carbs.
Carb "unmolested" or not?
