I had to replace the carb on my 350 as there was none when I got the car. I believe the correct carb for my car would have been the 7040250. I was able to get a 7040252 (I believe that is for a 455) very cheap that just needs refreshed/rebuilt. I'm guessing for optimal performance, I need to rejet the 7040252? Would anyone know what the correct jets would need to be or if anyone sells a kit to do the rejet?

Thanks.

 

The 250 has 070 jets,52 Sec jets, and 67 sec rods. 252 jets .070, sec jets 49 and sec rods 53

 

Here's the info I have:




edit: made a copy/paste error

 

The 455 is "fatter" as Harv points out.
As a baseline try running the carburetor with the existing 455 guts, see how it does.
Its not hard to change these parts on the car if it proves too rich.

The biggest concerns with a used QJet are bad filter housing threads, loose throttle shaft bushings and casting warp.
People tend to over tighten everything... the throttle body, the filter housing, the air cleaner wing nut.
You will be wasting your time if any of these problems exist.

The AVS door clock spring likely needs to be conservatively tightened (very sensitive setting performed on a running engine).
If its too loose it will (Qudra) bog on WOT.

Educate yourself before diving in blind unless you've tuned QJets before.

I tune carbs with a vacuum gauge.

To achieve optimal performance, super tune (calibrate) the carburetor in conjunction with the ignition curve.
The lame factory timing setting is a only a starting point, go up from there. Try 10-12 even 14° base.
Pay attention to the distributors vacuum and centrifugal advance curves. Total timing ~34-36-38°
The engine will tell you what it likes.

The AU secondary rods Fun shows are more desirable.

Use the highest quality parts you can find.
Look at the Corvette suppliers for the better ignition parts heavy duty points & condenser.
Taro makes USA wires, caps, rotors, points, & cond.

PARTS n BOOKS:
High quality carb parts: https://cliffshighperformance.com/
More parts: https://quadrajetparts.com/

How to books: Cliff Ruggles, Doug Roe & Every Day Performance. Start with Cliffs...I recommend all 3 though.

https://www.corvettecentral.com/
https://www.taroignition.com/

 

Late to the party....Delco 1970 document (attachment) in case you'd like a copy.

 

Interesting that Tornado 455 carb has the same primary rods and primary jets. The secondary rods are super easy to change. It could also be a different hanger too. Cliff's kit is super nice. His throttle shaft kit and instructions were good too.

 

'252 is for a Toronado. Not only is the jetting different, the throttle arm is different. Get the correct carb.

 

All good info. Thank you. I did notice the arm is different and have altered the throttle cable setup for that. I'll try a rebuild and leave the jetting as is and see how it runs. The carb body does not appear to be warped or damaged at all. I definitely would prefer to have the correct carb when my budget permits.

Thanks.

 

You can't see warp by eye.
Do yourself a favor and run the throttle body over a known flat surface with some wet n dry 400 & water.
Trust us on this. It will never tune if it's sucking air from a place it should not.

 

Will do. Thanks.