RE: [Chrysler300] 300C suddenly idles VERY rich

["chesnutt@xxxxxxxxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx>]

Hi Ray,
You may have a leaky float. They are brass.
I had this happen on our 1957 300C many years ago. I drilled a hole in the float where there was solder and drained out the gas. Filled the hold with solder and then put the float in hot water and no bubbles cane out. That fixed the problem.

Another problem could be that you are using the wrong Spark plugs. Since you are using A.G.R. 32 or colder they will foul in normal driving and will only last 3,000 miles or less. In the 1950's, I went through 40 of the AGR 32's before the Chrysler Dealer advised me to get a hotter plug. The AGR 32 would leave black smoke out the exhaust. Use a hotter plug (AGR 42) and your problem will go away.

In a letter from the Chrysler Division, Dated April 8, 1958, Mr. E. P. Carr, Car Engineering, recommends spark plug AGR 32 for high speed driving. For normal driving I use Auto-Lite AGR 42 or equivalent (warmer plug).

Also, I set my ignition timing between 5 and eight degrees advance. I have never used the factory setting of 4 degrees.
These old WCFB's have brass sight plugs on the driver side which can be removed to observe the fuel levels in all 4 float bowls. Take them out and check the float levels in the carbs. The fuel should just wet the threads at the bottom of the sight holes. Good luck.

I have been using non- ethanol gas since we seldom drive our 1957 300C.  Our regular driver is our 1970 Chrysler 300 Convertible which we have had for 32 years and also use non- ethanol gas.

John Chesnutt


-----Original Message----- 
From: Chrysler300@xxxxxxxxxxxxxxx <Chrysler300@xxxxxxxxxxxxxxx> On Behalf Of Ray Melton rfmelton@xxxxxxx [Chrysler300]
Sent: Tuesday, September 25, 2018 10:53 AM
To: Chrysler 300 Club, Int'l <chrysler300@xxxxxxxxxxxxxxx>; John L. Chesnutt <chesnutt@xxxxxxxxxxxx>using A.G.r 32 os 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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Posted by: Ray Melton <rfmelton@xxxxxxx>
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Posted by: <chesnutt@xxxxxxxxxxxx>
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