Re: [Chrysler300] 300C suddenly idles VERY rich

["paul paulholm@xxxxxxxxxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx>]

On 9/25/2018 1:53 PM, Ray Melton rfmelton@xxxxxxx [Chrysler300] wrote:
> Hello All -
>
> After a nearly five-year comprehensive restoration effort, my late
> father's 1957 Chrysler 300C convertible has been running and looking
> great for nearly a year - First place or "best of Show" at nearly a
> dozen local car shows, and lots of compliments, thumbs-ups and honks
> from other drivers!  But suddenly two weeks ago it began running VERY
> rich at idle, following an abrupt braking incident - now it almost
> wouldn't idle in gear, and I had to shift to neutral at every stop to
> keep from stalling.    I suspected the sudden deceleration had sloshed
> fuel from one of the carb bowls, and indeed I initially smelled raw gas
> under the hood.   But repeated attempts to "unstick" either of the carb
> floats by tapping  a wooden screwdriver on the tops were futile, and
> short bursts of full-throttle to 90 mph (shhh!) to perhaps flush any
> debris from a float needle jet did not clear the problem. However, once
> at full-throttle and high speed, the car runs GOOD and happy!  But
> nothing has stopped the return to severely rich idle.
>
> It now starts sluggishly (whether hot or cold) and only if I hold the
> accelerator all the way down to give it maximum air, symptom of
> near-flooding.  Hard revving from idle gives black smoke from both
> pipes, but it seems to run OK once the revs get above 1500 - 2000 (no
> tach).  I don't suspect a fouled plug yet, since it runs good at top
> end, and BOTH sides of the dual exhaust show black smoke, instead of
> black smoke and sooty tailpipe from perhaps only a single fouled plug on
> one side.  Don't smell raw gas under hood any more, but too-rich idle
> persists.

> Although I don't think it's relevant, it should be noted that I had just
> recently switched to 91-octane NO-Ethanol gas ($3.29/gallon) as soon as
> it became available in town barely a month ago (August).  I had
> previously been running 91-octane ethanol-adulterated pump gas with 25 -
> 50% 100-octane low-lead aviation gas from my local airport
> ($5.25/gallon)  But at this point, cost is not a consideration, and I
> may go back to the avgas mix as soon as I run out the new ethanol-free
> stuff, just to see what happens.

> I can't yet find the info in the repair manual, but I need to clarify
> whether the engine runs on the FRONT or the REAR carburetor at idle and
> low speed, because that's where the too-rich running occurs; when the
> second carb kicks in, it runs fine!  Can anyone tell me which carb to
> start trouble-shooting?

> NOTE:  Jim McGowan restored both carbs and performed the modifications
> outlined in Service Bulletin 1002-CH and subsequent correction in
> Technical Bulletin #364, which involved drilling new holes, lowering
> float levels and installing different jets and metering rods, which I
> had custom-made by the fellow who actually bought the original machinery
> that Carter used to fabricate the jets and metering rods back in the
> 1940's and 1950's - no modern carb specialist could hold the necessary
> tolerances, whereas this fellow says he can hold 0.0005", just like when
> Carter was making them over 60 years ago!

> I appreciate any help!

> Ray Melton   Las Cruces, New Mexico  white/Gauguin convertible S/N 3N572517

The Carby With the Choke!!   :-)

And I'm going out on a limb here, that should be the rear carby??
(I didn't go look, its a very dreary day here at this time)


-- 
Paul Holmgren
"The apparent lesson of the Inquisition is that insistence on uniformity
of belief is fatal to intellectual, moral and spiritual health."
     -The Uses Of The Past-, Herbert J. Muller


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Posted by: paul <paulholm@xxxxxxxxxxxxx>
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