General Category > Quadrajet Carb Talk and Tips

Lean condition at idle only

<< < (2/3) > >>

Cliff Ruggles:
Still a tad "low" for that camshaft if you truly have 9 to 1 compression in the engine.

In a stock 350/300hp engine with just a tad over 10 to 1 true compression and only 4 degrees initial timing you'll see at least 20" vacuum around 650-700rpms.

In a 9 to 1 350 with 12 degrees initial I'd expect at least 16" if not 18-19".

The carb has PLENTY of idle fuel for the engine specifications listed.  The 7044213 does have a pretty decent size upper IAB but it is offset by the .040" idle tubes and DCR's just over .050".

Do you see any improvement backing out the idle mixture screws a bit more?

If not might want to check the size of the holes under the mixture screws and open them up just a tad, to .86-.090".  Some of those later emission years carburetors had tiny holes to limit how much fuel you could add at idle speed even when they didn't put limiters or covers over them........

jberenyi:
Thanks Cliff.  I'll check how big those mixture screw exit holes are when I get home after work.  BTW, do you typically open those up when you build someone a carb or reserve that option to be done later if needed?

Cliff Ruggles:
I typically leave them at the stock size for stock or very close to stock applications.  If I get the carb on the test engine and it acts like it's limited for idle fuel deliver I'll take a look there before taking the top back off.

For what you are doing unlikely you'll need larger idle tubes or DCR's, at least if the cam is actually the correct part and intake isn't closing too late from a stretched out timing set, etc....

jberenyi:
I opened up the mixture screw exit holes to .089 and it runs much better at idle now.  If I cup my hand over the airhorn it barely raises the rpm with mixture screws out about 6 turns.  I was thinking of opening it up a little more but my friend was afraid to let me LOL.

jberenyi:
I might go to .093 allowing a little more flow and less turns on the mixture screws this weekend.  Thoughts Cliff?

Navigation

[0] Message Index

[#] Next page

[*] Previous page