Re: [Chrysler300] 300C suddenly idles VERY rich

Ray:

Years ago, I had almost the identical problem with my 1976 Chrysler NYer quadrijet. Turned out that the floats were non-metallic and eventually soaked up the gasoline to the point where they sank and allowed the carbs to run ultra rich. Replaced them with metallic floats and never had another problem.

Dan Reitz

Bell Canyon, CA

In a message dated 9/25/2018 11:10:00 AM Pacific Standard Time, Chrysler300-noreply@xxxxxxxxxxxxxxx writes:

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

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