Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

7041251 tuning...

(1/3) > >>

Tancuda:
Hi everybody,

I would like your suggestion on what I could do to have better vacuum and idle...

The carb (7041251) is rebuild (stock) by a known rebuilder in the US.
 
What I know: 71 jets, 49b prim.rods, AK sec rod.
                    Choke work well, acceleration and cruise is ok.

Engine: 1970 455 (low comp) with headers
Cam lift is .448 INT, 456EXH, unknown duration.
Compression was 135 to 145.
Base timing 14, dwell 30
Plugs are pretty white with good gap.

What I did:   Did send it back to rebuilder last year and he said that he had enriched the idle a bit
                    but I don't see any improvement.

                    Idle mixture screws are out 7-8 turns
                    If I put my hand over the carb, rpm rise and my vacuum is much better (14 to 18)
                 
                   Checked vacuum leak with carb cleaner around intake and fitting with
                   all hose disconnected (PCV, brake booster, trans modulator, distributor)

                   No leak except a little one around secondary throttle shaft.
                 
                   So I really think the carb is the problem.
                 
Is there something I can try that wouldn't need the carb to be taken apart ?

Do you think that with today's fuel, the stock spec on that carb is wrong ?

Thanks a lot.

           

lightning boy:
Tancuda, if you can post some pics we can tell if the carb has been rebuilt by the wrong outfit. Hopefully your "rebuilder" is someone who specializes in Qjets. Unfortunately, you need to take it apart and measure a few things to see where it's at. Looks like it needs more idle fuel.

77cruiser:
With that low of cranking comp. it could use more timing too.

Tancuda:

--- Quote from: lightning boy on December 15, 2025, 01:05:32 PM ---Tancuda, if you can post some pics we can tell if the carb has been rebuilt by the wrong outfit. Hopefully your "rebuilder" is someone who specializes in Qjets. Unfortunately, you need to take it apart and measure a few things to see where it's at. Looks like it needs more idle fuel.

--- End quote ---

Thanks for the reply, yes the rebuilder specializes in Qjets, here some pics on and off the engine.
The carb is 7041251, and also I would like to know if it's the correct baseplate (7029025).

Thanks

Tancuda:

--- Quote from: 77cruiser on December 15, 2025, 02:55:00 PM ---With that low of cranking comp. it could use more timing too.

--- End quote ---

Thanks for the reply,
Yes I can bump timing but my total will be too much.
Would have to play with the advance in distributor. I wonder how I can't have it right with the stock setting ?

Thanks

Navigation

[0] Message Index

[#] Next page