General Category > Quadrajet Carb Talk and Tips

QJet tuning on SBC 350

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Cliff Ruggles:
I don't like to use "K" series rods with those units, as they only allow .005" of tuning ability on the upper section.  I'd set it up with a full tapered rod instead.

"M" series don't work well in large MAB carburetors.

I can supply idle tubes, tuning parts, and anything else that you need for it when you are ready......Cliff

kfa670:
Well, this thing has about frustrated me enough haha.

I can tune for an awesome mid-range or an awesome top end, but can't seem to get both.  And always rich off idle with puffs of black smoke.

So, what kind of recipe would you suggest for this carb? 

Idle tubes?
Rods?

I understand I may have to play with the mains a little to get it just right, but would you suggest altering any other parameters of the idle circuit?  Let me know and I will place an order

Thanks

kfa670:
I forgot to mention I tried a few different combinations:

.071 Mains
44K rods (from Cliffs HP)

-This has given me the best mid-range and a pretty decent idle so far.  A small hesitation off idle and some black smoke.  Pretty flat feeling on the top-end.  This is the best I have gotten the truck to run.

.076 mains
.052Ms

-Attempting to keep the mid-range the same and add just a little more fuel on top-end.  Mid-range sucked, Top-end a little better, idle and off idle not great. 

The best vacuum I can ever get at idle is about 14g.  I'm at about 6000k elevation. 

You mention using a full taper rod... would that be the older style?  I didn't think they would work that well in a newer unit?

And again, if you can put me a list together for a good kit for this MAB, I'm more than happy to get out the credit card :)  Had enough of taking this thing off and putting it back on...

Thanks again for all the help!

kfa670:
Or should I just quite messing around and put some smaller MABs in this dang thing too....

omaha:
yes, high altitude can present some problems. I think airbleeds would be a good move. Maybe somewhere in the .070 to .080. range. Slower pump shot (outside hole) and less stroke would help. You got less air  out (up) there so less fuel to go with the less air.  full taper rods would be more adjustable. maybe a lower tension spring in the APT so you don't over fuel it. Most of us "flatlanders" carbs will smoke if we take them up to those altitudes. That is why you need the slower fuel curve. Also the heavy weight of the vehicle . maybe .034 - .036 in the idle tubes. The idle transitions into the off idle so it is important to have it set up right. This is my opinion only and I know others may have more, better advice on the set up but I think the general direction would be this. good luck and don't give up now, youll get it figured out.

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