Chevy Production Guru Questions / Q-jets

[imdarren]

Chevy production Guru's help with this please?

Did Chevrolet really quit installing Q-Jet's marked 7041xxx December 31st 1971, and start installing 7042xxx carbs January 1st 1972?
Would they use up the 7041 (1971 carbs on the 72's until they were gone)?

My 72 K20 Cheyenne Super has a carb (from1975) that needs rebuilt, and I have a 7041xxx Q-Jet I could send out to have rebuilt, but want a correct number carb for my truck.

Any Chevy Production Guru's out there know what Chevrolet's production practices were?

Thanks. Darren

[imdarren]

Ok. Maybe a better way to do this.
Could any of you who are confident you have the original Q-Jet on your truck read the numbers off the drivers side of the carb please, and post them?
This way I can figure out if they only used 1971 marked carbs on 1971 trucks, and 1972 marked carbs on 1972 trucks etc. Trying to learn a bit here.
This would be good info, and maybe save this in some tech archives on the board.
Thanks for the help.

Darren

[70cst]

ttt

[Tuff Gong]

#7041211

[70shortfleet]

7042218-1972 gmc 402 bb

[cpisani70@aol.com]

7041206 71 C-20 402
Posted via Mobile Device

[DANTIP]

The factory service manual has a chart of carburetor numbers for each engine/trans/emission combination available. I don't have my manual handy, but maybe someone would post a scanned page for you. This is the best way for you to narrow down your search.

[slikside]

First off: I am no guru.....but, here's what I found out when rebuilding my carb.

I thought I had an original Q-jet when I decided to rebuild it. I soon discovered that it was built in Dec of 1976! At first I was a little bummed, but I got Cliff's High Performance book and used his parts and some services (base plate bushing/primary throttle shaft) and found out that the later model q-jets are much improved carbs over the original design.

So unless you are going for a completely original restoration, the later model q-jet will be a much better carb for performance.

Funny thing is, I have had this truck ('72 C-10 SWB) for nearly 30 years, and had forgotten that the po had told me about the different carb. Seems they had quite a few problems with the earlier q-jets.

Good luck on your rebuild whichever you decide. This is a great 'Upgrade" if you will...my truck hasn't run this good in...well, about 30 years!!!

[oldgold70c10]

Originally Posted by slikside

First off: I am no guru.....but, here's what I found out when rebuilding my carb.

I thought I had an original Q-jet when I decided to rebuild it. I soon discovered that it was built in Dec of 1976! At first I was a little bummed, but I got Cliff's High Performance book and used his parts and some services (base plate bushing/primary throttle shaft) and found out that the later model q-jets are much improved carbs over the original design.

So unless you are going for a completely original restoration, the later model q-jet will be a much better carb for performance.

Funny thing is, I have had this truck ('72 C-10 SWB) for nearly 30 years, and had forgotten that the po had told me about the different carb. Seems they had quite a few problems with the earlier q-jets.

Good luck on your rebuild whichever you decide. This is a great 'Upgrade" if you will...my truck hasn't run this good in...well, about 30 years!!!

Everything he said is spot on. The early original 4m series Q-Jets will have issues that will need addressed to make them reliable carbs for daily use. That said, they were made until 1978, so if your absolutely set on using a 4mv, you can easily do it and have a newer carb that doesn't leak, etc. Your early style throttle shaft can be substituted into the later base, so your throttle linkages look/work the same.

However, if your more interested in ease of setup, reliability, get a modified Q-jet, the M4M Q-jet made from 76 and up. They have the integral choke that can be easily converted to electric choke, and one you get them setup, you can easily forget the vehicle has a choke. Throttle linkages can be a problem, but I had Cliff Ruggles rebuild a 77 baseplate and he was able to easily install a 70-72 throttle lever to the throttle shaft. 4M and M4M throttle shafts will not interchange. If you go this route, Buick and Pontiac carbs are the best unless you have to have the Chevrolet style side inlet.

[68 50th]

This is from the 72 Service manual:

[imdarren]

Dang! You guys are great!
Thanks for scanning the book and posting it. Sweet deal.

Mostly I was having a hard time believing Chevrolet had tight supply chain management, and actually cut off Q-Jets with 1971 dates at the first of the 1972 year. But Chevrolet made many thousands of vehicles each year, so I guess it's not far fetched to think previous date carbs would NOT carry over into the next year.

Yah, I'm just trying to get the correct carb number for my Cheyenne Super. It's a K20 A/C truck, and will be really nice when done, and I'm trying to collect the correct parts along the way. Just to have them mostly. Some of these old parts are getting harder and harder to find in decent shape.

Maybe I'll send out the 17057229 that is on there now, and have it rebuilt, since they were built better, and just run it, and find a correct 7042208 to keep for the numbers matching value later.

You guys have been very helpful as always. Thanks

Darren

[PatrickGMC70]

Well, I am also not an expert, but...

I don't think it would be a change at Dec. 31 - it would be when the model year changed over, not the calendar.

When you think about it, it's probably not that crazy an idea. It wasn't that they had to have enough carbs so that they ran out on a specific date. Instead, they knew how many vehicles they were going to produce, and just ordered that many 71 carbs. When they began the next model year's production, they started with the newer carbs.

Obviously, I wasn't there, but it makes sense in my head.

[DANTIP]

Originally Posted by PatrickGMC70

Well, I am also not an expert, but...

I don't think it would be a change at Dec. 31 - it would be when the model year changed over, not the calendar.

When you think about it, it's probably not that crazy an idea. It wasn't that they had to have enough carbs so that they ran out on a specific date. Instead, they knew how many vehicles they were going to produce, and just ordered that many 71 carbs. When they began the next model year's production, they started with the newer carbs.

Obviously, I wasn't there, but it makes sense in my head.

I agree on the model year change. The reason is because of the strict emission requirements. Each engine had to be tested and "certified". Once "certified" the manufacturer was not able to make changes. I suspect that is why my TLM engine code 402 was actually made in late 71 but is correct and certified (see your emissions label) for my 72 model year truck.