Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet part number 7029282

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Chris_Oz:
Hi,

I am also in Au and am just learning the Joys of tuning a Qjet.

71 to 76 jet change is HUGE, that is a 24% increase in effective jet size on cruise and a 17% increase when on the thin end of the needle.

Try to keep changes UNDER 10% or you will get lost. Do you have any smaller needles, a .042 would give you a 8% increase.

The float should be right at 10mm, if you didn't have the hesitation before, the high float level may have been hiding it as it dumped fuel down the throats.

Your carb should have APT, have you adjusted it? Did you reset it back to factory after you rebuilt it?
What Piston spring are you using? If the spring is too weak or you have low vacuum, it can cause a hesitation until the secondaries start feeding it.

Do you have Cliffs Book?

Cliff Ruggles:
What size are the main airbleeds in the airhorn and main casting?  On the Chevy carbs built for US engines in that period they were nearly 1/8".

Up until 1969 the Chevy units used very small MAB's just under .050".

Fuel delivery to the engine is effected much more by the MAB sizes than by which jets and metering rods are used.

Float level also effects fuel delivery as does the size of the fuel inlet seat.  Very few kits have the correct N/S assembly in them so the smaller hole lowers the fuel level some even with the correct float height.

I would use a .135" N/S assembly and set the float to 1/4" (.250") and leave that alone.  We do NOT tune these carburetors by moving the float height it is done by using the correct parts, settings, then jets/metering rods/PP spring to get the engine running correctly in all areas.......Cliff

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