A few QJ things for your consideration. I worked my way through grad school
doing QJs for
local shops and tune up joints.
The single biggest QJ problem is jet well leakage. To facilitate (make
cheaper) production the QJ were
produced with holes on the bottom of the jet wells. This allowed the jet
mount to be taped from the
bottom most likely reducing a couple of machine steps in production. The
jet wells were sealed with
lead seals over time they ALL LEAKED some sooner some later. Many carb tune
up kit of the 70s
included a piece of crappy foam to put pressure on the seals to try and
stop the leakage, This fix
does not work particularly well.
Since your QJ is most likely aged it would be best to disassemble it and
catch a few other things.
The base on your older QJ is most likely cast iron so wear should not be a
problem but check
the butterfly rods for wear anyway. With the carb disassembled tap the lead
seals with a ball peen
hammer (flat side) to reseat them then use the peen end to dress up the
edges. Then use a high temp
chemical resistant (not 5 minute) epoxy to cover all four jet well seals.
Replace the needle and seat
and make very sure the float is not saturated (plastic) or leaking (brass)
and is adjusted properly.
You can adjust the QJ mixture but the technique is not for the faint of
heart. First you have to make sure
you have tapered mixture rods not the stepped ones. If you do then this
will work. The QJ mixture rods are
vacuum controlled with a spring return ie: the spring pushes them to a rich
position open throttle more fuel
close the throttle vacuum increases mixture rods are pulled into the jets
closed throttle less fuel. With this
in mind I'll tell you how I used to do it. The area I lived it was about
5000 ft above MSL so some leaning
of the 60s and 70s car was called for. I removed the mixture rod vacuum
piston and spring and cut about
1 and 1/2 turns off of it. This set the mixture rods lower in the jet for a
specific vacuum and thus leaned out
the mixture. This is a last resort after doing all of the carb servicing
above and should not be attempted
by anyone without a clear understanding of the consequences of screwing it up.
Hope this helps Jerry
>>
>> My GMC seems to running very rich. The tail pipe has some carbon black
>> deposits on it and when I run it for a long idle the floor shows some
>> black carbon film on the condensed water.
>>
>> Is there a small adjustment (not changing jets) of the Qjet to lean out
>> the mixture some?
>>
>> Any suggestions will be appreciated.
>>
>> Marcus
>Before you adjust anything, be absolutely sure that the entire intake
>tract is unrestricted and the air filter element is clean and flowing at
>least as much as stock.
>
>Terry Wallace
