Re: Fwd: Re: [Chrysler300] 300C suddenly idles VERY rich

["Ray Melton rfmelton@xxxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx>]

Hi John and others -

Thanks for the input.  Yesterday I was able to remove the air cleaners and found that the choke flap (rear carb) was fully closed (with correct gap), although I had made certain to NOT touch the throttle since the last shutdown, when the engine was hot and the choke should have been pulled off.  So, certainly the engine had been running with the choke flap closed (at idle when last shut down), although since the choke flap is mounted on an offset pivot shaft, high airflow through the carb (at heavy throttle) will keep the flap open as long as there is high airflow.  I believe that's why the car ran crappy rich at idle, yet would run strong and clean at higher revs, especially  all the way up to ~ 90 mph, but then the offset-pivot choke flap would return to closed at low throttle and idle, causing obvious rich condition.  The choke plate linkage seems free of any stiction.  I'm fortunate to have a solid-state Pertronix kit hidden in the distributor, aided by a matched high-voltage 40kV Pertronix coil (painted and labeled to look stock) and new-generation fine-wire NGK Iridium spark plugs (one step hotter than stock), so no indication of plug fouling, or it would've laid down on top end.  I looked in the manual and see the "choke pull-off" linkage, but am still figuring out how to test it for functionality; the hot air tube from the right-side head to the black choke bi-metal spring "pot" appears intact, so I think next I will remove that cover on that heat-activated choke pull-off "pot" and see if anything appears amiss, like a broken or disconnected bi-metal spring, although I doubt I'll find a problem there because rotating the black plastic housing does indeed reposition the choke flap.  For now, I merely rotated the round black plastic choke activator until the choke flap is fully open (no choke at all) even at "cold" start.  ("cold" here in New Mexico September means about 75 degrees.)  Now, the car starts quickly, idles normally, and runs clean and strong at all throttle settings, then returns to normal burbling idle.  No black smoke when revving hard from idle.  Although I've only run the car about 15 miles (highway and side streets) since resetting the choke flap, at this point, I don't think I'll even mess with disassembling the carbs to check for float levels (not a trivial task considering all the linkages!) unless I encounter further carburetion problems.   But I still can't figure why the "overly rich" condition would have occurred so suddenly - in barely two seconds!   Engine was warm and running fine, then instantly went "full choke = too rich" after an aggressive braking maneuver.  WTF?  There's a strong chance my problems are NOT entirely caused by the choke flap!

Does anyone have any thoughts about how to test the "choke pull-off" mechanism?  All I see in the service manual is how to set the necessary gaps and bend a tang to get the right clearances, but nothing to check actual function.  Maybe put a hot-air gun on the black plastic choke activation "pot" to simulate the action of the hot-air tube from the head?  If the hot-air gun actually pulls the choke off, then maybe the hot-air tube is inoperative.  That hot-air tube connects to the back of the head on the right (passenger) side, so it is really buried under the heater airbox, etc., and is virtually invisible and unreachable without removing a lot of parts.  If I disconnect that hot-air tube at the choke "pot" on the carburetor, is it correct to assume that it's a closed system whereby the heat from the head merely heats the stagnant enclosed air in the tube?  I don't think it's plausible for an actual "Flow" of hot air from the head into that tube - what would be the incoming air source and where would it exit?

P.S.  NOTE:  There is a spurious notation in a previous forwarded message that said I was running AGR 32 (Autolite?) spark plugs - I am certainly NOT, and I have NO idea where that erroneous information came from!  I'm actually running modern NGK fine-wire Iridium spark plugs BKR5EIX-11, which are approximately one step hotter than the old-generation AG42 plugs that were supposedly standard back in the day.

Ray Melton

On 9/29/2018 12:10 PM, John Holst wrote:

-------- Forwarded Message --------

Subject:	Re: [Chrysler300] 300C suddenly idles VERY rich
Date:	Fri, 28 Sep 2018 21:40:41 -0500
From:	John Holst <jholst@xxxxxxxxx>
Reply-To:	jholst@xxxxxxxxx
To:	chesnutt@xxxxxxxxxxxx

Hello Ray, the previous responses were all good advice. I have another story to pass along on my 1964 300 K. Also had a hard starting, ran too rich all the time and the plugs were fouled with carbon . Over the winter I would try and run the car once in awhile just to keep seals from failing with age. Each time I would start the car it would not idle and required running at a higher RPM for a few minutes to allow the car to run on it's own. Discovered an attachment on the carb called the primary Choke Pull off was not working at all. The flaps were staying closed and too much gas was running into the carbs. After I was able to find a replacement it turned out to be for a 1965 car which indicated that it had been changed out sometime in the past.Took only a few minutes to screw on the new part and now it runs great. Checked the plugs recently and they were normal. Just a thought. John Holst...

-----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: Ray Melton <rfmelton@xxxxxxx>

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