Hi,--You really should go back to stock ,— it is not just jet size , it is the profile of the tapered mixture control rod responsive to vacuum across the rpm range and the operation of the vacuum advance curve just off idle which were all carefully designed. And all that are ruined , compared to factory calibrations by say operating the two carbs at once . Or low vacuum due to a hot camAdd in that lower vacuum if cam has been significantly stepped up and that leads to lots of problems . I think the 300 had 280 advertised duration on the hemi , pretty hot for a street motor. You go more , idle has to go up some. you get stalling then when pushing drive . And no power at 1000 rpmToday they would add a loose converter can’t do that with the old torque flite.They worked very hard to get a balance between performance and drivability , they did very well . It is not a race car now, 375 hp you can use is a lot better than 400 that barely runs unless you are at 135 mph . ( if you ever get 400, often you lose hp)In an absolute 2022 sense they are not fast cars anymore , rather classics that we can drive , —-souping up a well balanced ,well thought out 392 as one might safely do to a stick Chevy 283 brings nothing but grief .But almost all of us do this once .. (smile )I did it to a J , cam and trans shift kit ,It shifted at 6000 + or so blew off all the belts , wrecked a few radiators caused me to walk a bit . Stalling on engaging , hassles with power brakes.Older now , would think twice .On this —- first step is go to totally stock carb operation, if that does not solve it , you may need to go to 280 or less cam .What cam duration is in it now?“ great mechanics “ do not know more than the guys who designed it ,ran it , set records with it when new , that is just a fact , sort of ? Right ? They sorted it all out , probably 30 of them .. engineers.Pump shot if poor might help , but that has to be way off to really hurt , — but be sure it is working . I have encountered in last few years where check balls or brass check valves in that part of carb get crud on them from (?) ethanol , kind of a white deposit , when sitting a year or so . No pump squirt= can’t start car but will run once started . FYI . ..John GSent from my iPhoneOn May 7, 2022, at 4:27 PM, Ray Melton <rfmelton@xxxxxxx> wrote:True - But in this case, how does the mechanic know what size to drill? And which jet(s)? And in rear carb only or both? Are replacement jets available if the bigger jet produces no change or makes things worse? Drilling is largely irreversible.
Good instrumentation on a series of chassis dyno runs could really help pinpoint the problem and lead to optimum performance. (Lotsa labor changing jets - assuming you have alternatives readily available - and making adjustments in between runs = pretty costly, but even at $100/hr could be worthwhile investment. ) Unfortunately, I don't have access to such facilities anywhere near my small town in New Mexico.
A good place to start with the carburetors is with Chrysler Service Bulletin #1002-CH, Dated March 1, 1957. (Available through Club website - Technical) And of course, the Factory Service Manual.
Personally, I would go back to the original stock progressive configuration, ensure baseline adjustments per the Bulletins and Service Manual, then perform the recommended carb modifications and go from there.
Ray Melton
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On 5/7/2022 1:58 PM, Gary wrote:
--Gary G.With a No. and letter drill set you can dill jet to any size you need.GaryFrom: Gary GettlemanSent: Saturday, May 07, 2022 12:25 PMTo: Ray MeltonCc: 300 ClubSubject: Re: {Chrysler 300} Need more fuel!Ray,Thank you for your way over my pay grade response.Mechanic is very talented and has some very high $$$$ builds to his credit.That said, his main business is high end Resto Mods.Did a buddies '41 Cad coupe on Art Morrison frame with 2021 Cadillac Hot Engine and 8/10 ? speed tranny.Very High end builds, yet he will work on old Detroit iron like our beloved 300's.I like your suggestion re the service bulletin update and will start there and let you know how it goes.Best Regardsgary gettlemanThe once "Golden State" (but not so much any more) of California.--On Sat, May 7, 2022, 12:07 PM Ray Melton <rfmelton@xxxxxxx> wrote:
Hello Gary -
Sounds like it could be insufficient accelerator pump shot. Which jets is he suggesting to be changed, and to what size? How did your mechanic decide which jets to change and the new size - anything scientific or just WAG? How will you find those jets for such an obsolete carburetor? Even if jets for the later Carter AFB would fit, is the internal fuel/air flow circuitry the same as for the WCFB? Since the 300C was originally intended to run on only one carburetor at low RPM, you may have upset the A/F ratio right off idle when you converted to synchronous (non-progressive) carburetor function - going too lean because of the unintended extra airflow from the other carburetor. Have you incorporated the carburetor modifications recommended by Chrysler in Technical Bulletin #364 of July 16, 1957? That may/may not help, but it couldn't hurt. I had Jim McGowan do that mod when he restored my carburetors - excellent workmanship and results!
Depending on the elevation where you primarily operate, you might also want to consider different metering rods, too, although that will not affect your off-idle stumbling issue.
Ray Melton 300C in New Mexico
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On 5/7/2022 12:31 PM, Gary Gettleman wrote:
To All the Great Folks in 300 Land.--Apparently the cam that we installed during the C engine rebuild is a bit lumpy as compared to the stock cam.Have what I would call a momentary stutter when the right foot presses down.We adjusted carb linkage so instead of running on 2 barrels it's now on 4, which has improved performance, but still get the occasional hiccup.Mechanic said we need to swap out the jets for larger size and that will solve problem.Figure someone else has had this problem and would appreciate your help with this issue.Thanks to all.gary gettleman300 C Export
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