Any insight to this small problem would be greatly appreciated.
I have a Rochester four barrel Q-jet currently on my chev blazer, 350 sb,
It is a great carb. Performs well, provides relatively good mpg. Chokes up
on cold mornings. Overall, there is notning wrong with this carb. Except
one minor annoying detail.
After an appropiate period of time for proper warm up, the choke kicks down
appropriately. But when I wait at a stop light it seems to take 30 or more
seconds for the idle to return to a normal point, somewhere about 750 rpm.
Seems the engine idle hovers around 1000-1100 for maybe even a minute. Then
begins to slowly drop down to the normal range. I have tried adjusting
everything external on the carb with out being able to correct this problem.
I have adjusted my timing multiple times. I have adjusted the idle-air
mixture multiple times. Like I said other than this minor inconvienience,
this is a great carb.
Any suggestions for what may be going on and how to potentially correct this
would be greatly appreciated.
Are you sue that the engine is thoroughly warmed up? This carb uses a
step cam for the cold idle and if the choke has not pulled off
completely, it will sit on one of the lower steps of the fast idle cam.
Also, is the vacuum break adjusted/functioning properly? You may have
the choke set too rich or it may take longer than you expect for the
choke coil to respond.
I would rather be exposed to the inconveniences attending too much
liberty than to those attending too small a degree of it.
~ Thomas Jefferson ~
Rich, thanks for the reply. I'm damn certain that the electric choke coil
is functioning correctly, and that the cam is stepping down incrementally as
the engine warms up. Oddly enough, in the morning is when I actually get
the best idle quality. After the cam has stepped down the engine is rock
steady at 750 rpm. Only after a few more lites does the "slow return to
idle" difficulty set in. I've searched hi & lo for manifold or carb vacumn
leaks, checked or replaced every vacumn hose. Still, I'm chasing a ghost.
This may not be your problem, mine stalled randomly, at lights.
The QJ has a gasket that has 4 bushings in the corners. This is to
keep you from warping the throttle body, when torque it down.
With age, this gasket shrinks, and allows air to enter around it, the
bushings holding the carb in it's original position. The fix is to
replace the base gasket, periodically.
This happened once on my 70 Grand Prix, and twice on my 78 Jimmy, in
You don't say what year -- Sticking advance weights will cause the
fast idle you describe, but the engine will appear to run fine,
otherwise. This is a common failure, in the HEI distributer, the
rotor punches through, and the voltage jumps to, and erodes the
advance pivot pins. This will creat red rust dust in the distributer,
and is obvious. A clean up and replacement of cap and rotor will fix
this problem, you may need more work if the pins are worn badly.
base On Mon, 15 Sep 2003 15:40:36 GMT, "Willis Layton"
Colorado Springs, CO
My advice may be worth what you paid for it.
Thanks Dan, The application is a '84 Chev Blazer 350 sb. I'm fairly certain
that the distrib. is doing ok. That was one of the first things I thought
of and checked. Rotor, cap, and advance mechanism seem to be fine. I do
like your suggestion regarding the insulator gasket between the intake
manifold and carb. Thats just the kind of simple problem that will probably
cause the symptoms I'm experiencing. I replaced the carb a couple of years
ago, and foolishly did not replace the gasket. At that time I remember
noting that the insulator was sorta dryed out and brittle. I imagine that
it may have cracked or warpped over the intervening years and is probably
sucking air somewhere. Although I did do the kerosene mist trick around the
manifold seal to the block. Passed that one.
I have developed a simple axiom when trying to diagnose a fix to a problem:
"Whats the simplest thing that can be wrong." And that's probably it!
May have overlooked the obvious on this one. Keep you posted.
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