Author Topic: Olds Qjet recipe.  (Read 335 times)

Offline Kenth

  • Carb lover
  • ***
  • Posts: 81
Olds Qjet recipe.
« on: October 19, 2019, 12:17:27 PM »
Looking for the recipes on 7040255 an 7040256 Quadrajets.Anyone knows or where i can find the sizes of:
1. Idle tubes.
2. Upper idle air bleeds.
3. Idle down channel restrictions.
4. Lower idle air bleeds.
5. Idle screw discharge ports.
6. Main air bleeds in airhorn.
7. Main air bleeds in bowl.
8. Primary nozzle air bleeds.
9. Primary accpump jets.
10. Secondary initial pullover discharge jets.
11. Secondary well emulsion tubes.
12. Secondary well filling holes.
13. Wide open airvalves opening distance to back of chokehousing wall.

Thank you!

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 4321
Re: Olds Qjet recipe.
« Reply #1 on: October 20, 2019, 04:48:22 AM »
I just did one about a week ago but didn't write down the specs (7040255).

It had no power piston and straight off the jets.

Very tiny MAB's and small jets.

No bypass air in the baseplate but drilled primary plates.

The 7040256's are similar but not exactly the same.  Pretty special carburetors and rare as they don't use a primary power piston and primary metering rods. 

Most likely they decided the huge cams used in the 350 and 455 engines just wouldn't work well as there was pretty low vacuum at idle speed......Cliff

Offline Kenth

  • Carb lover
  • ***
  • Posts: 81
Re: Olds Qjet recipe.
« Reply #2 on: October 20, 2019, 08:32:04 AM »
Thank you Cliff!
I am setting up a 7040253 for a 1970 W31 missing the correct carb.
« Last Edit: October 20, 2019, 08:35:32 AM by Kenth »

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 4321
Re: Olds Qjet recipe.
« Reply #3 on: October 21, 2019, 04:51:21 AM »
It is difficult to duplicate the factory calibrations for the carbs that didn't use a PP.  The upper MAB's are really tiny and jets were pretty small.

I've built quite a few for those engines and used a PP and they work fine, just have to set it up with plenty of idle fuel and correct PP spring.

I'd also add that the early Ram Rod carbs for the 350's used a power piston in 1968, they didn't eliminate it till the 1970 models far as I know.  The 1968 calibration was pretty generous for an early Olds carb, but it works well......Cliff