Rochester Carburetor Issues

[Pat M.]

Hello everyone, my 70 came with a Carter Carburetor, and it worked fine until recently, when I noticed it was leaking fuel at the fuel inlet fitting.

After speaking with several people, they said that the long-thread repair fitting, nor the helicoil repair procedure would work on a Carter, because supposedly the metal around that fitting is soft and thin.

So, for safety reasons I decided to replace it with a rebuilt Rochester carb. A trusted mechanic friend of mine put in the Rochester and it doesn't seem to "want" to idle. It's fine at about 1300-1400 rpms, but dies when you try to slow it down.

Vacuum measurements seems fine, and we can't figure it out. Any suggestions? Thanks

[Mark E.]

If it's rebuilt by a commercial service, it may be junk. They are often Frankenstein carbs with components from a variety of Q-jets mixed together during volume production.

Post some close up photos and the numbers from the original and rebuilt carbs.

IF the Carter unit is original to the car, it may still be your best option. Contact CliffsHighPerformance.com or Lars (contact information on CorvetteForum.com) and ask about options for its salvage.

Next best option is to find an original core and have one of these guys restore it.

[Pat M.]

Hi Mark, thanks for your response.

See attached. First is Carter code, next are rebuilt rochester codes.

[David M.]

Pics of the bad fuel inlet. We need to see the threads up close.

NO QuadraJet (QJ) will work out of the box to 100% of its capability. Yes a Carter is a QJ, by design, just made by Carter.

Do you want to learn how to do this yourself? Do you have the aptitude, patience, and basic quality tools to rebuild a carb?

Get Cliff Ruggles and Doug Roe's books and read.

They are not hard to tune IMO if you take your time have the right parts and have a vac gauge. But then I've been at it since 1980 so I'm a little biased regarding zero intimidation and simplicity of a QJ. There a few YouTubes that are worth watching.

You could use the new float bow with your OEM carbs parts installed in it. IF the castings are a match. Compare.

You could send your OEM out for professional repair/rebuild.

You could pull the guts out of your OEM and install into the new carb...primary jets, both rod sets and AVS cam etc... But it will still need to be tuned.

Start with a call to Cliff and get his parts. He'll talk your ear off as long as you dont ask real stupid questions. He's not rebuilding anymore, I think I got his last 3 carbs.

Nothing beats a well tuned QJ.(and a well tuned distributor)

https://cliffshighperformance.com/

https://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189?crid=108P34HJZIVGQ&dib=eyJ2IjoiMSJ9.JSM Puo2HG7SbOBgUouzglmctuvcHPOT1gmcM_k7bfarGjHj071QN2 0LucGBJIEps.3CqZPD-aSD5RAjoKOtc95Qr7nkjmLB1F7POn38veEXk&dib_tag=se&ke ywords=cliff+ruggles+quadrajet+book&qid=1746578721 &sprefix=cliff+Ruggles%2Caps%2C157&sr=8-1

https://www.amazon.com/Rochester-Carburetors-Revised-Doug-Roe/dp/0895863014?crid=5PDOJQZHNT7Q&dib=eyJ2IjoiMSJ9.KYiE xVfu3eKzE2Gby3FpUhbbrUd3lxCe6MIkCugrc_k.Cb6YVC5-8Cqn8v9T2Y34VuF9wjbNZ-j44Dh4_2KW_lU&dib_tag=se&keywords=rochester+carbur etors+by+doug+roe&qid=1746578757&sprefix=Doug+Roe% 2Caps%2C137&sr=8-1

[Mark E.]

I can't read the numbers on the Carter. It looks like you have a 300hp 4-speed, so the original the pn should be 7040203 or 7040213. The 5th digit will be 5 if it's a California car (RPO NA9). Its date should be within about 6 month of the car's build date. If it's the original, it may be worth restoring.

The rebuilt unit is a replacement Edelbrock 1901 Quadrajet (no longer produced)... at least the fuel bowl is. It was made on the 267th day in a year ending in 8. I believe Edelbrock started producing these in the 90s.

[Pat M.]

Hi David and Mark.

I don't have the Carter carb with me me right now, but it has @ 2-3 threads on the intake fitting, and I don't have the ability to try to repair this by myself.

The Carter carb reads 7040203 DB K9.

Thanks for your help, best regards

[Mark E.]

Hi David and Mark.

I don't have the Carter carb with me me right now, but it has @ 2-3 threads on the intake fitting, and I don't have the ability to try to repair this by myself.

The Carter carb reads 7040203 DB K9.

Thanks for your help, best regards

That's the right PN for the car. What's its date?

Contact one of the resources mentioned above to have them repair the threads. David is correct- Cliff has stopped restoring carbs but he can refer you to a resource.

Using the original Q-Jet will provide the most reliable performance and enhance the value of the car.

[Pat M.]

That's the right PN for the car. What's its date?

Contact one of the resources mentioned above to have them repair the threads. David is correct- Cliff has stopped restoring carbs but he can refer you to a resource.

Using the original Q-Jet will provide the most reliable performance and enhance the value of the car.

If I'm reading the TIM and other sources correctly the date is "K9" = October 1969.

I realize that date is out of line with NCRS's normal 6 month rule (my car has a May build date), but I'm convinced it's the original carb for this car. The part number is a production code for a 1970 4 speed, and my original dealer's copy of the tank sticker clearly shows the car came with a Carter. Moreover, the previous owners of the car didn't care about "numbers matching" stuff. What are the odds they either on purpose or mistakenly found a production coded 1970 Carter carb for a 4 speed?

I will look into the resources mentioned.

Thank you and David for your help.

[Mark E.]

If I'm reading the TIM and other sources correctly the date is "K9" = October 1969.

Good catch. I forgot Carter Q-Jets have a different date code format. What's the date on the car's trim tag?

[Patrick H.]

This is not a repair you want to do on your own.

You can send the whole carb (the original) or just the main body to someone like Custom Rebuilt Carbs, or Cliff's High Performance. Ideally you would want someone to recolor the body once the new helicoil is installed, as any "open" or exposed metal will start to corrode.

I would not waste time with the rebuilt one you purchased. You will spend more time, and possibly money, on it than just having your original fixed.

And as already noted, it's a Rochester built by Carter, not a Carter-designed carburetor.

[Pat M.]

Good catch. I forgot Carter Q-Jets have a different date code format. What's the date on the car's trim tag?

Car's trim tag is 5/70

[Pat M.]

This is not a repair you want to do on your own.

You can send the whole carb (the original) or just the main body to someone like Custom Rebuilt Carbs, or Cliff's High Performance. Ideally you would want someone to recolor the body once the new helicoil is installed, as any "open" or exposed metal will start to corrode.

I would not waste time with the rebuilt one you purchased. You will spend more time, and possibly money, on it than just having your original fixed.

And as already noted, it's a Rochester built by Carter, not a Carter-designed carburetor.

Thanks Patrick. Based on what you all have said, I'm going to try to salvage the original Carter.

[Mark E.]

Car's trim tag is 5/70

7 months after the carb's date is officially beyond the 6 month judging guideline, but quite possible in the real world, IMO. Depending on the week in October and May, the time span may be 6 months plus a week or two.

Lots of inventory fluctation isn’t surprising then. GM had terrible production and inventory control plus this was the aftermath of a strike.

[Pat M.]

7 months after the carb's date is officially beyond the 6 month judging guideline, but quite possible in the real world, IMO. Depending on the week in October and May, the time span may be 6 months plus a week or two.

Lots of inventory fluctation isn’t surprising then. GM had terrible production and inventory control plus this was the aftermath of a strike.

That's my opinion as well. Given all the evidence it seems far more likely this was an exception to the normal time frame for parts.