So the carburetor must need more accelerator pump shot, right?
The engine is a 493, MP 528 cam, Demon 850 with vacuum secondaries. The acc pump cam is the pink one. I have a set of new pump cams to test but before I do, I'm curious as to how strong of a stream I should be seeing.
For comparison, the Thermo quad I was having trouble with now has a steady stream but a much smaller width stream than my Demon. On the Demon, The lever rests right on the cam and the other end rests right against the pump arm. There is no slop there. It does immediately push fuel but not like a strong stream one might see after a few beers.

More info: The stumble is just off idle. Anything over 1900 rpms or so it is fine. Given my rudimentary carburetor knowledge, does this condition mean that the primary circuit is in play and the acc. pump isn't as crucial?
Also, it seems that this is a recent development. I'm wondering if the pump cam started wearing or if the turn to colder weather (35-55 degrees) is adding to the problem. The Charger is not driven daily, just when time and weather allows.

I'll also add that this stumble is both in neutral and when the car is driven. Thanks.

Before doing any more with the carb, as part of a diagnostic procedure, try advancing the timing 5 or 10 degrees and see if the stumble goes away and report back.

I was thinking the timing may be too far advanced and causing a hesitation.A demon 850 is a Holley 4150/4160 style carb correct?Check for a bad diaphragm(fuel leaking under bowl) or a clogged acc pump shooter/passage.

I will. It was set to 18-19 initial and 33 total but maybe it slipped? The idle speed is consistent though, say 950 in Park/Neutral.

How fresh is the fuel? Old gas doesn't vaporize very well, and summer gas isn't good for winter.

Check to see how much clearance you have between the pump arm and the pump diaghfram (SP?)at WOT. If it is more than .015 to .030 adjust the bolt longer until you get .015 left
Also check the size of the squirter nossles, they may be to big. I like .031 to .035 I.D. at the largest on my Holley type carbs

The gas is a few months old when it was in the high 60s/low 70s. Not quite Summer blend but I wondered about the fuel.
I didn't check the acc. pump/lever clearance at WOT. Good idea, I did read that some time ago.

Make sure the pump lever is adjusted right (should not have clearance in the idle position). You should really start by upping the squirter size before the cam, at least according to Holley. Jump 2 sizes and see if there is a difference. If not jump 2 more. Still no difference? Change the cam. Rinse and repeat.

That said if you don't have any nozzles start with the cam. The pink cam is junk. The blue cam is the most aggressive and will likely fix your stumble, may be too much though.

Is it a slight stumble just as you lean on the gas a little. Or is it when you get aggressive with the throttle?

If it is the first, look at additional initial timing, richening the idle mixture screws, larger IFR, or less IAB. Could be a vacuum leak too.

""It was set to 18-19 initial and 33 total""

""The acc pump cam is the pink one.""

""The stumble is just off idle. Anything over 1900 rpms or so it is fine""

"" if the turn to colder weather (35-55 degrees) is adding to the problem""

Depending on the carb, you may need to readjust your idle A/F ratio as the outside temps change. If you have the carb tuned for 60-80 degree weather, then you may need to richen it up for the 35-55 temp days. Since you say anything over 1900rpms is fine (transitioning from Idle Circuit to Main Circuit), then I would suggest richening up your metering screws (Idle Circuit). Since you have an A/F guage, and if the car does not have this issue in warmer weather, then I would start with idle A/F reading that you used in the warmer weather. The cooler weather will lean out the A/F readings (Idle to WOT) with no other changes to the carb. If you had 13.5 at idle in the warmer temps, then aim for that again and see how it reacts. If there is still a problem, then try 13.2 or so in the cooler temps.

The Pink cam is the leanest cam off idle. If you still have the stumble after you reset your metering screws, then I would swap cams from the Pink to the White and retest. If the White does not totally cure it, then test the Orange cam. The Blue cam is the largest and because of that, it would be my last test. Work your way up in pump cam sizes until the problem goes away. You may find out that you need a smaller cam in the warmer months (Pink/Black) and a larger cam in the cooler months (White/Orange).

I don't think you mentioned squirter size. But if you are already in the .031"-.037" now, then the "red flags" that I see are the temperature change (Metering Screws) and the Pink cam.


""It does immediately push fuel but not like a strong stream one might see after a few beers.""

That would be the same comparison as to the Pink cam versus the Blue cam!

30cc cam sizes smallest to largest in OA volume (Black, Pink, White, Red, Green, Orange, Blue). The Black, Orange and Blue have the most fuel off idle, then the White/Red/Green are the next aggressive off idle, then the Pink cam is way down there as far as fuel off idle. But if the carb is setup rich enough at idle, then the Pink cam would do fine.

Thank you very much. This stumble did just start happening. I do not know the squirter size. The carburetor is basically stock with the exception of having different jets, power valve and primary metering block.
I printed out the graph showing the "curves" of the different cams. Wow...This pink cam really is weak in comparison!

I got a little free time today so I tinkered with the car.

Timing is right where I left it. 18-19* initial, 33-34* total.

I took this info and also looked at the brochure that came with the Demon carburetor. I read where it stated that in some cases, there may be an off idle stumble if the idle mixture screws are LESS than one turn out. I checked mine and yes...the left side was 1/4 turn from being seated and the right side was about 3/8. I backed them both out to rest at about a full turn open and the stumble disappeared.

Strange thing though: The car seems to run the strongest at AFR numbers richer than what is considered correct. I have had bigger jets in there giving me cruise and WOT numbers at approx 13.0 and 11.0, numbers that are supposed to be too rich. I've rejetted to lower those numbers but it seems to cost power.
The days before these AFR guages I guess people tuned to the best idle vacuum and by reading the plugs. My plugs are always a bit black. Not as if they were painted black but still nothing like the plugs coming out of a late model car or truck.
I;m not drag racing the car so it isn't as if I am trying to squeeze every fraction of power at the expense of drveability. I do want it to run as clean and as efficient as I can get though.
Do oxygen sensors give false readings when they go bad or do they just fail? I ask because a couple of years back when I first installed the guage, I was dealing with those pesky detonation problems. I ran about 2 1/2 gallons of 110 octane Sunoco to see if more octane would stop the knock. That gas was leaded. I've wondered how much leaded fuel has to be ran through an engine to contaminate the sensor.

I would and do shoot for 14.5 AFR or leaner at idle and light part throttle cruise That should really help keep the plugs clean What brand and heat range plugs are you using? You may need to lean the transition fuel feed down also to get those readings As far as WOT AFR shoot for from 12,5 to 13.3 on pump swill, richer will FEEL better but the car will run better at the track with those readings Sometimes the butt dyno lies to us the time slips don't

Do you run E10 now?
What heat range plugs are you running?

I thought that I read that O2 sensors did not like leaded fuel, but I would assume that if that is true, it would have to be on a daily basis and not once mixed in.
If your car runs better cruising at 13.0 when others say it's best at 14.5, then run your 13.0! There are so many variables that will not allow all engines to run at the same A/F. Do your testing and reference what others say.
I have read that some can cruise at 15+, but my testing shows me that I am safer at 14.0-14.4 with E10. I also idle richer than some other auto guys at 13.4-13.6 and some 4 speeders can idle at mid-high 14's and plus.
Test and test some more until you find what works for you.

First, find the idle A/F that works for you.
Second, tune the transition A/F that works for you (off idle up to 45-60mph cruise)
You will also need to tune the PV/PV Restricters/Main Jetting/ and Primary HSAB's for acceleration. Then tune your secondary jets/HSAB's for WOT last.

I have limited knowledge of tuning the carburetor. I understand the basics of jetting, power valves and the accelerator pump. Once you get into stuff like the air bleeds, PVCRs and such, I get lost.
Awhile back, I dropped a wrench on my original metering block when I was changing jets. The wrench cracked that hollow plastic vent extension and I couldn't find another one. I switched to a Quick Fuel primary metering block with screw in plugs/jets for the PVCR and emulsion bleeds. I figured that these differences, it might help fine tuning.

AFR at 14.7, which I assume is what you are calling the "correct" ratio is not correct as you found out.

It is correct for emissions purposes. It is not correct for max power, richer usually is as you found out. It is not correct for max economy, as you will find out. With a carb and a wide band O2 you can datalog your changes and dial in the best ratios for WOT and cruise. It's more tedious a procedure than an EFI setup but it is doable. All the various adjustments you mentioned are there to dial in the setup. I am by no means a Holley guy so I cannot comment on it but many here can.