Re: IML: 1967 Imperial Coupe / Carburator Help

[Mike Pittinaro <mechimike@xxxxxxxxx>]

> I recently installed a new edelbrock performer in my
> vehicle, the car seems 
> to idle fine but I cannot seem to get the thing
> adjusted corrrectly.  The 
> vehicle keeps backfiring, not sure if this is
> another issue all together.

The settings for the carburettor and timing, etc, will
vary based on dozens of factors from vehicle to
vehicle.  That said, it sounds like you may have an
issue with improper timing, or a mixture issue.  These
are my guesses.  What I would do, once you've
eliminated any possible leaks (hoses, gaskets, etc) as
sources of gremlins, set the carburator mixture screws
at exactly 2 turns each out from just barely bottomed
out.  Don't turn the screws in tight, or you WILL
damage the needle points.  Start the car, and adjust
the base idle (vacuum advance disconnected and the
hose from the carburettor plugged), so the engine is
idling at spec- check the FSM, I think its 600 RPM in
nuetral.  

Now we play chase the tail.  You want to set the base
timing to something around 5 to 10 degrees BTDC.  If
the engine is fairly fresh, no carbon buildup on the
pistons, and you're running 92 octane or better
(perhaps with some additive for lead or octane boost)
then you can go closer to 10.  If its an old engine,
that's been idled alot (carbon buildup on the pistons)
and you're a cheapo who uses 87 octane goat urine, set
it closer to 5.  

Once you've set the timing to something you like,
reset the idle to 600 RPM.  Now, play lean drop with
the carburettor- turn each needle valve screw 1/4 turn
out until the engine speed stops increasing the more
you turn them out.  Then, start turning them in 1/4
turn at a time until the engine speed starts
decreasing when you turn them in.  Now reset the idle
speed to 600 RPM.  

Having done all that, and reconnected the vacuum
advance to the distributor, let the engine warm up to
operating temperature- 160 to 195 degrees F, depending
on your thermostat.  Park the car on a nice open area,
get in, hold the brake pedal firmly and give it some
gas.  DON'T do this for more than 5 seconds, or you
could damage the transmission.  Just listen for
pinging while doing this.  Also, don't spin the tires.
 Just load up the engine at a higher RPM and see if it
pings.  If it does, back off the timing.  If not, you
can up it a little and recheck.  You want it as high
(advanced) as possible without pinging under load.  

Once you've set it here, do some test drives uphill in
high gear at 30-50 mph using as much throttle as you
can without it kicking down into 2nd.  Again, check
for pinging, and adjust accordingly.

The guess and check comes in when you re-adjust the
timing, the engine may want a slightly different
mixture, so you can get into a loop of adjusting
mixture and timing back and forth.  The law of
diminishing return applies here, though.

=====
--Mike Pittinaro

Beautiful Boxcar
American Grandeur and
Danish modern Style


		
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