Quadrajet Problem Solving > Quadrajet Parts and Numbers

Restamp 7040256 ID

(1/5) > >>

4speed455:
I bought a beautifully restored restamp carb. It is stamped 7040256 which is a 1970 W30 4 speed carb, but is an obvious restamp. The pad shows no casting detail that would normally be present under the stamp, so it was machined off and restamped. Looks like it was setup close to the specs of a true 0256 carb with 58 jets and no power piston or primary rods and BE rods(should be AU). I want to add a power piston and primary rods and change the secondary rods and jets so I can use it on a stock cam 1968 Oldsmobile 455 with performer manifold, headers and HEI. I bought the book and some micro drill bits so I can measure everything. This is what I came up with so far. Upper idle air bleed is in the main body, float fulcrum is the early design and idle pass air is present.

Idle tube: not removed or measured yet
Idle channel: .046
Lower idle air bleed: .070
Upper idle air bleed (main body): .070
Accelerator pump discharge holes: .026
Main air bleed (main body): .060
Main air bleed (air horn): .040
Secondary POE well restriction: 0.36
Secondary POE restriction: .052
Secondary tube restriction: .035

Looks like everything matches what a 1970 Oldsmobile carb should have came with originally from the best I can tell. Also most measurement match recipe #1 except the MAB are smaller, which appears to be correct for an early Olds also.

I have 58, 70, 72, 73, and 76 jets as well as BE, AU, BP, CH, and CV secondary rods already but only the 49c priamary rods. My plan was to set it up as a 7040251 with 49c primary rods, AU secondary and 70 jets. Should I drill the MAB and use different rod/jet combo or leave the MAB and go with a more traditional olds setup? Also what size idle tubes should I have with the 49c/AU/70 combo?

Let me know if you need any more information or if you suggest any other mods, thanks Joel.

4speed455:
Besides the idle bypass it also has 7/64 holes drilled in front of the primary throttle plate. Cliffs book says some “high-performance” quadrajet used 3/32 holes but these are bigger then that. I’ve also read that these are more common on olds then other brands.

Kenth:
The 49c/AU/70 combo would be a nice start.
I would use .052"-.055" idle down channels and .038"-.039" idle tubes.

Also, your carb has a Carter made Chevy base plate and with .109" idle bypass air no need for drilling the throttle blades.
And the choke pull-off rod sits upside down and in the wrong direction for the proper function.

Cliff Ruggles:
Good find Kenth, not exactly sure how you could install one of those backwards but it's on there that way?

You will have trouble tuning the carb without a working APT screw in the baseplate if you convert it to a power piston style carb.  49 rods are pretty "fat" on the upper section and teamed up with .070" jets you will need the ability to raise and lower those rods.

The Chevy baseplate will probably work, but it is different in several areas than the Olds variety including the length and location of the transfer slots, another good reason to have a working APT system.  I'd add here that "Frankencarbs" and commercially "remanufactured" carbs are the most difficult to tune, so prepare yourself.  This simply happens because of the differences in the parts used to build them, plus "builders" often make changes in several areas which are seldom for the better.

As far as tuning it will matter which "stock" 455 1968 Olds engine you are going to use it on?  Olds made several different 455's and specific camshafts for them, which determines the "tune" required to get it to work well.

I would also recommend getting one of my high flow N/S assemblies (non-windowed) and one of my accl pumps at a minimum even though it is a "fresh" rebuild.  If it has a brass float in it toss that in the trash and get a float for it as well........Cliff

4speed455:
Thanks for the suggestions. First off the choke pull off rod was installed upside by the prior owner after opened it up to check the setup, it has been noted the correct orientation. As far as the base plate what tells you it’s a carter Chevy plate it has a similar casting number to the other carb pieces? It does appear to have APT installed complete with adjustment screw and tension spring. The opening is still capped so it doesn’t appear to have been messed with. As far as the cam it was originally a high compression 2bbl motor with the mild cam. As far as the idle tubes and down channel restrictions I thought I read that olds used smaller opening to work with the fatter 49 primary rods and the smaller 70 jets? That’s why they used smaller MAB from my understanding. I am still a newbie and here to learn though. Thanks again.

Navigation

[0] Message Index

[#] Next page