Rich and Stumbling

Matthew68

Well-known member
Hi Folks, running into an issue with a stumble upon acceleration and carbon fouled plugs. It's a new build for the whole motor, new carb (rebuilt by KP Carbs from the old Pony Carbs). Details and issue below:

Build
200ci, 30 over zero decked
VI Aluminum Head/Intake
YT Roller Rockers
Schneider 270/270 cam, 110 LSA 2* advance
Stock C4, stock converter
Approx 10:1 compression
Autolite 2100, 1.23v @ 356cfm currently 55f jets
Recurved DSII by WSA at 18 degrees advance

Issue
I tuned using a vac gauge for smoothest idle and highest vacuum, approx 14mmHg (decent cam, stock C4). I know I'm running rich based on carbon fouled plugs and some black smoke out of the exhaust. It idles in park fine around 850, but as soon as I drop it in gear the idle becomes very low and rough, sometimes sputtering and it wants to die. Some accelerator or adding some choke will help, but that's a bandaid. If I tap the accelerator, it will move and get up to speed (slowly). If I give it any more than 25-50% throttle, it sputters and dies.

I've checked the float, seems fine. Carb was rebuilt and restored so I'm not worried about internals being gummed up. I'll be installing an AFR gauge in the coming days, but I'm wondering if it's the jets. I've adjusted the air fuel screws, adjusted the accelerator pump (currently at the outside whole, and the second from the top) and tried different settings with nothing really helping. No vacuum leaks I can find, fresh gaskets on the carb mounting bracket to intake and gasket at the carb. I pulled the plugs today and they were all carbon fouled.

Other than jets, which I have a few coming my way, any other things I should be checking or potential culprits? I've done all my tuning and testing with the air cleaner off as well.
 
How did you check the floats condistion? Did you check the wet fuel level? How did you check for vacuum leaks? With the vacuum gauge hooked up ideling in gear (D) what dose the gauge needle do? What power valve rating are you running? Do you have a good tach to use? I probally wouldn't be changing out the jets yet until you get it idle really good and have dialed in the accelerator pump so it can take off from a stop with out stumbling. One other thing to note is that a stock stall speed torque convertor isn't a very good choice for your combo of parts. Best of luck :nod:
 
bubba22349":10x21nhx said:
How did you check the floats condistion? Did you check the wet fuel level? How did you check for vacuum leaks? With the vacuum gauge hooked up ideling in gear (D) what dose the gauge needle do? What power valve rating are you running? Do you have a good tach to use? I probally wouldn't be changing out the jets yet until you get it idle really good and have dialed in the accelerator pump so it can take off from a stop with out stumbling. One other thing to note is that a stock stall speed torque convertor isn't a very good choice for your combo of parts. Best of luck :nod:

Thanks, Bubba.

Float condition: I removed the horn cover, unclipped the float and inspected for any holes, leaks. Did not find any. I needed to remove the float regardless to check what sizes jets I had in. I did not measure wet fuel level.

Vacuum leaks: I sprayed carb cleaner around all four sides of the carb, including at the mounting plate to the intake manifold. I did not get any idle changes upon spraying.

Idling in gear: I did not check out vacuum or accurate RPM in gear. I have an old style external Sears analog tach unit/engine analyzer. I do not have a tach inside the car.

Power valve: not sure. I will check this week.

For my accelerator pump, which settings on the up/down holes would give me the most shot? Outside or inside hole as well? Perhaps I can change a few more settings.

Stock stall: I realize that isn’t the best choice. Eventually the trans will be pulled for a rebuild a higher stall or a T5. When I did the motor I wanted to future proof it for those updates realizing this.
 
Hi, 2 things. If that was my engine I would want to try another carb on it. Do you think the fuel pressure is too high? Good luck
 
B RON CO":25e3vxm9 said:
Hi, 2 things. If that was my engine I would want to try another carb on it. Do you think the fuel pressure is too high? Good luck

Hi Bronco,

Not sure on the fuel pressure. I have a stock mechanical pump.
I wish I had another carb to try, but I don’t. This is the only one I have.
 
Hi Matthew68, Dry Float Level should be 3/8 inch. On accelerator pump shot the lever hole closest to the throttle shaft is the A and goes up to D. A gives the longest pump shot your at B right now which should be good to start. On the other end at the pump lever on fuel bowl you have an inter and outer hole you should be on the inner hole this gives the quickest shot. Actually on Autolites the its called an Economizer Valve sorry about misstating the name, in reality it does the same thing as a Power Valve on a Holley and the Holley valves are interchanable with the Autolites, Holley Power valves are easier to get somtimes and have a bigger selection of ratings. To get to access to your Economizer Valve the carb needs to be unbolted from engine its mounted under a four screw cover plate on the bottom of the fuel bowl. Pony Carb's was a great company so probally everything is done right. What i am leaning in the direction of is that the Economizer valve is the wrong rating for your engine combo this will take some testing using your vacuum gauge mounted so you can see it good while your driving, such as at a take off from a start. These valves can cause trouble somtimes by being defective or the wrong vacuum rating, or a bad gasket from being over tightened these will cause it to be too rich. If you pull off the carb check the base gaskets real good or post some pictures of them some base gaskets don't seal properly to intake.

That excellent that your have the Sears tach unit I would like you to reset your carb idle mixture screws starting by lightly bottoming out the mix screws then set to a setting of 1 1/2 turns out. With engine warmed up good to operating temp turn each of the screws out until you get the highest idle RPM then turn the screws in 1/4 turn to lean the mixture this is the lean best idle mixture. Next set the curb idle RPM with the trans in drive park brake set or someone in the car hold their foot on the brake. This idle RPM should be around 550 to 650, but the engine needs to be able to keep running smoth enough. Repeate the mixture screw adjustment and the the crub idle again to see if it changes any. Once this is set you can see how it takes off from a stop if it's still stumbling then start adjusting the accelerator pump shot timing to dial that in. At that point it will be time to dial in the Economizer valve. Once that's dialed in you can check on the jetting with your AFR gauge. Hope that helps you some. (y) :nod:
 
Possible blown power valve on a leaking one.
Dump it & get the Modified Holley i have for sale in the small ford six section for sale.
Flows as much as a Holley 390 4bbl.
Set the idle in P to 1000 RPMs.
 
bubba22349":3ckgmo00 said:
Hi Matthew68, Dry Float Level should be 3/8 inch. On accelerator pump shot the lever hole closest to the throttle shaft is the A and goes up to D. A gives the longest pump shot your at B right now which should be good to start. On the other end at the pump lever on fuel bowl you have an inter and outer hole you should be on the inner hole this gives the quickest shot. Actually on Autolites the its called an Economizer Valve sorry about misstating the name, in reality it does the same thing as a Power Valve on a Holley and the Holley valves are interchanable with the Autolites, Holley Power valves are easier to get somtimes and have a bigger selection of ratings. To get to access to your Economizer Valve the carb needs to be unbolted from engine its mounted under a four screw cover plate on the bottom of the fuel bowl. Pony Carb's was a great company so probally everything is done right. What i am leaning in the direction of is that the Economizer valve is the wrong rating for your engine combo this will take some testing using your vacuum gauge mounted so you can see it good while your driving, such as at a take off from a start. These valves can cause trouble somtimes by being defective or the wrong vacuum rating, or a bad gasket from being over tightened these will cause it to be too rich. If you pull off the carb check the base gaskets real good or post some pictures of them some base gaskets don't seal properly to intake.

That excellent that your have the Sears tach unit I would like you to reset your carb idle mixture screws starting by lightly bottoming out the mix screws then set to a setting of 1 1/2 turns out. With engine warmed up good to operating temp turn each of the screws out until you get the highest idle RPM then turn the screws in 1/4 turn to lean the mixture this is the lean best idle mixture. Next set the curb idle RPM with the trans in drive park brake set or someone in the car hold their foot on the brake. This idle RPM should be around 550 to 650, but the engine needs to be able to keep running smoth enough. Repeate the mixture screw adjustment and the the crub idle again to see if it changes any. Once this is set you can see how it takes off from a stop if it's still stumbling then start adjusting the accelerator pump shot timing to dial that in. At that point it will be time to dial in the Economizer valve. Once that's dialed in you can check on the jetting with your AFR gauge. Hope that helps you some. (y) :nod:


Ok, so I took the PV cover off and it was not leaking and dry, which is good. However, I have no stamp on what size it is. See photo. I’m putting the carb back on an making some accelerator pump adjustments and idle mixtures, but not sure what to do about the PV.

I’m 400’ over sea level and average around 14mmHg on vacuum. Should I order a 6.5 or 7.5? This is if nothing else works in terms of accelerator pump changes.

Pic here: https://imgur.com/gallery/OXOJLxh
 
Look at the side of Economizer valve will have its markings on the edge of the hex flats, carb rebuild kits may come with a 6.5, 7.5, or 8.5 this denotes at what vacuum the valve starts to open. The 14 HG average reading isn't very helpful in determining the right Valve rating that you need to use. To be able to know which rating you would need to use you need to hook up a vacuum gauge to a manifold vacuum sorce for an accurate reading while the engine is idling. Remember that a stumble can be caused by either being too rich or to lean since as you indicated above that your plugs are dark so as you stated its way too rich i.e. the valve could be opening to soon.

Yes so in order to narrow down the problems the very first thing you need to do is to reset the idle mixture screws correctly and then set the curb idle RPM with your tach. The vacuum gauge needs to also be hooked up and the engine is warmed up to operating temp. For an Auto Trans car you want to get a vacuum reading with engine idling with the Trans in Drive. With a Manual Trans car the Vacuum reading is with the engine idling in Netural. When you have this reading then devide that number by 2 this is Economizer / Power Valve rating you what to get or order, it should be right on if the carb idle mixture and curb idle is adjusted correctly see my above post for the details.

Next after those two steps are done, if when taking off you still have a stumble you could try adjusting accelerator pump timing but only do one of these changes at a time so you know the effects of each change. If I had to guess with your cam and what you are describing of how it's running I would say it might need a 6.5, 6.0, or 5.5 vacuum rated valve, but I would much rather first see the actual vacuum readings when its idling in Drive as its a much more accurate way to do it. Afterwards you can try both an easy and hard take off from a stop for further testing of a stumble to better dial in the accelerator pump. Then the very last thing to do is dial in the main jets to get your cruse AFR right. Best of luck (y) :nod:
 
Your problem is the stock 1650 torque converter, transfer slot and brass well tube configuration. The 2 bbl Autolite of that 1.23 carb venturi is set up for an early H code Windsor 351 to 400 non FE V8, or a simioar size AMC 290/304/343/360 and has one less hole in each well tube which makes it richer off idle. Go back to a five hole 4 bbl 4100 1.08 or 1.12 well tube or drill an extra 25 thou hole in the top of each well tube . The idle needs to be leaned back to avoid the rich stumble you are trying to fix with a leaner jet.

Contact users Peter62 or Crosley at Hughes Perfromance and ask about a 2350 rpm, 2.53 stall C4 200 converter based off a Pinto spinner.

See the two carb recondition sites Ill link below, but talk with KP and send them a link to this post.

2 stage power valves, if they fit your housing, or if you get a Jeep one, tend to restrict richening from the Power Valve channel restrictions. This is a crutch which always helps engines that have a too rich unloaded, too lean off idle condition caused by a lack of idle and transition vacuum.

Your options are open. You can respond to Bills kind offer, or do the research and have KP and Hughes dial in the correct parts to fix this air fuel related idle and off idle problem

Every Aussie guy knows Carb signal changes not at all between a 250 six and 302 2-bbl, or a 265 six and a 318 2-bbl, but on our small sixes, as soon as its cammed up, or has power steering, a/c or a new rope seal, its just too much to ask a 351 2bbl 1.23 carb to operate in a 200 environment with a huge plenumb and a very efficient aluminum head.

I put a 390 FE 2100 1.33 on a 265 Hemi 2-bbl...it worked fine, but a 200 is half the size of the engine that carb was designed for..

Walking Tall's site for carb rebuild info

https://carb-rebuilds-plus.boards.net/

https://www.tapatalk.com/groups/racingfuelsystems
 
dats nuz ta me...
:cool:
:unsure:
 
Xctasy, makes a very good point the smaller Autolite or Motorcraft 2V carb's off a 289 or 302 V8 is a direct bolt on and easier to tune on the small sixties. Not that you can't make your bigger carb work with some effort to mix a little more air in to lean out the idle circuit. Check his other posts link below for more info on fitting a two stage power valve and checking out the K clusters well tubes. Good luck (y) :nod:

Xctasy's Post on Autolite / Motocraft 2V
viewtopic.php?f=1&t=76966&p=592413&hilit=Autolite+well+tubes#p592412
 
First, try the basics. A good deal of tuning work-a-rounds are incorrectly set or absent. A 170 hp 200 small six is different to tune because Detriot never had big 2V carbs on aluminum head in lines with big cams and a large runner in take. The only thing close was the early Hyper Pack Slant Six Valiant V200 package.

Try Uncle Tonys Garage Jeep or AMC bleed back gasoline filter.

https://youtu.be/-t6geNGbEXM

A common problem is air fuel mixture swing when hot. Which Ford corrected starting 1963 on Air Con Lincolns Mercury and high end Fords with the Hot Engine Idle Compensator, a bimetalic strip which corrects air fuel by air bleed at high temparture when fuel is perculating. If you 1.23 carb is from an AC car, it will probably have one on or by the air horn.

Example of one car with bleed back, and the problem when bleedback is removed.

https://youtu.be/7svmL2mfpKE
 
Tony, always w/the cigarette (& backwards hat). Seen 'em w/o the ciggy, never w/o the hat? "Kinga da Mopwrs" :nod:
 
What is the initial ignition timing?
Larger cams with increased overlap require more initial timing.
 
pmuller9":2n2363i9 said:
What is the initial ignition timing?
Larger cams with increased overlap require more initial timing.
18 degrees initial.
 
HI Matthew68, have you made any progress on your carb tuning? :nod:
 
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