Original vs. Service Replacement Quadrajet

[Mark E.]

Other than its date, how can a service replacement Quadrajet be distinguished from an original?

Would it be stamped with the same part number as the original it replaces? Or would it have a PN identifying it as a replacement?

[Edward J.]

Re: Original vs. Service Replacement Quadrajet

Mark its pretty much the same carb, the part no. stamped on the side may have one of the digits that is not the same, and off coarse the date will be different. I had a serv. replacement on my 72. and found a properly dated carb for my car later on before I had it judged.

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

Other than its date, how can a service replacement Quadrajet be distinguished from an original?

Would it be stamped with the same part number as the original it replaces? Or would it have a PN identifying it as a replacement?

Mark------


It depends upon when the SERVICE carburetor was manufactured. If it's close to the time that the original carb was manufactured, then the SERVICE carb will be identical (assuming the original carb was ever available in SERVICE). As time goes on, things change. Part number consolidations occur and part number supersessions also occur. In addition, other minor features may change over time even if no part number change occurs.

By the way, no Q-Jets are currently being produced, either by GM or any other manufacturer and none have been produced in a very long time.

[Patrick H.]

Re: Original vs. Service Replacement Quadrajet

If it's close to the time that the original carb was manufactured, then the SERVICE carb will be identical (assuming the original carb was ever available in SERVICE).

Joe hit the nail on the head. He could probably give specifics, but there were many carbs that were not in service for very long, if at all. Others were seemingly in service forever because one part number "serviced" many in the field.

[Tom L.]

Re: Original vs. Service Replacement Quadrajet

Hi Ed, just wondering what the number on your service replacement carb is. I have a '72 LS5 and the carb is a 7042220 dated spring of '72. Runs great and looks like an original except for the last two digits, silly numbers : )

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

Hi Ed, just wondering what the number on your service replacement carb is. I have a '72 LS5 and the carb is a 7042220 dated spring of '72. Runs great and looks like an original except for the last two digits, silly numbers : )

Tom------


The 7042220 carb was originally used on most 1972 Chevrolet passenger cars with big block. It was not originally used for Corvette. However, I would expect it to be very similar to the Corvette carb. There should be some difference but I don't know what it is.

[Tom L.]

Re: Original vs. Service Replacement Quadrajet

I have checked the data. From what I've read it is the exact carb, metering rods and all, aside from the last two digits in the part number.

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

I have checked the data. From what I've read it is the exact carb, metering rods and all, aside from the last two digits in the part number.

Tom------


I have no doubt that the published specs are the same for both carbs. That's exactly what I would expect. Nevertheless, there's got to be some difference in the carbs. Likely, it's some feature not covered in the specs. At least, not covered in the specs that we have available.

[Justin S.]

Re: Original vs. Service Replacement Quadrajet

Mark, I was told that the service replacement carbs have a triangular casting on the front side below the accelerator pump.

[Mark E.]

Re: Original vs. Service Replacement Quadrajet

Mark, I was told that the service replacement carbs have a triangular casting on the front side below the accelerator pump.

That's interesting. I don't recall noticing that before, but I'll look for it.

[Mark E.]

Re: Original vs. Service Replacement Quadrajet

Mark------


It depends upon when the SERVICE carburetor was manufactured. If it's close to the time that the original carb was manufactured, then the SERVICE carb will be identical (assuming the original carb was ever available in SERVICE). As time goes on, things change. Part number consolidations occur and part number supersessions also occur. In addition, other minor features may change over time even if no part number change occurs.

By the way, no Q-Jets are currently being produced, either by GM or any other manufacturer and none have been produced in a very long time.

Are some Q-Jet PNs unique to service replacements? Or did service replacement carbs use a PN also used on a factory installed carb?

In other words, is there some way to tell if a Q-Jet began life as a service replacement?

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

Are some Q-Jet PNs unique to service replacements? Or did service replacement carbs use a PN also used on a factory installed carb?

In other words, is there some way to tell if a Q-Jet began life as a service replacement?

Mark------


Yes, some Q-Jet part numbers are SERVICE-only part numbers. For the most part, this involves part numbers that were supersessive to the original part numbers. As I mentioned previously, some original part numbered Q-Jets were never available, at all, in SERVICE but were SERVICED by a different part number, either an original part number for another application or a SERVICE-only part number.

If one has a Q-Jet of an original part number for a particular car with a date that could have been used for an original carburetor for a particular car, there is no way to tell if that carburetor started life installed in PRODUCTION on a car or started life as a SERVICE carburetor.

By the way, Rochester SERVICE part numbers were not necessarily the same as the on-carb part number even though the carburetor in the box might carry the original-on carb part number. In fact, usually the SERVICE part number (i.e. the number in the catalogs and on the box) was not the same as the number on the carburetor.

Rochester was one of the first GM divisions to start using 8 digit part numbers and I believe that's because Rochester NEEDED lots of part numbers and ran out of 7 digit part numbers early-on.

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

That's interesting. I don't recall noticing that before, but I'll look for it.

Mark------


I am quite sure that Rochester did not use different carburetor component castings for PRODUCTION versus SERVICE carburetors manufactured at any given time. However, as I mentioned previously, certain things evolved over time. It's very possible that by a certain time, perhaps long after a particular carburetor was used in PRODUCTION, features such as the one mentioned were added to SERVICE carburetors for earlier applications (as well as PRODUCTION carburetors for later applications).

[Peter S.]

Re: Original vs. Service Replacement Quadrajet

Hi Mark,

Justin may be referring to a specific case (at least that I know of), though perhaps it extends to other models. At least for the 7029207 L46 carburetor for 1969, an easy tell tale of a service replacement is the triangular mounting pad for some accessory. The one without the mounting pad would be a correct configuration for this original, specific carburetor in 1969.

I cannot say that this is the same case for the 7042220, but I wanted to provide some clarification to Justin's post.

[Joe L.]

Re: Original vs. Service Replacement Quadrajet

Hi Mark,

Justin may be referring to a specific case (at least that I know of), though perhaps it extends to other models. At least for the 7029207 L46 carburetor for 1969, an easy tell tale of a service replacement is the triangular mounting pad for some accessory. The one without the mounting pad would be a correct configuration for this original, specific carburetor in 1969.

I cannot say that this is the same case for the 7042220, but I wanted to provide some clarification to Justin's post.

Peter-----


What's the date on the SERVICE carburetor shown?