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  1. #1
    FEP Senior Member waggin's Avatar
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    Default YFA Carburetor Tuning Help

    Can someone give me a little direction in trying to tune my YFA carb? (1bbl carb on 1978 200ci I-6)

    I rebuilt it, then noticed when tuning the mixture screw for maximum vacuum, the farther out I turned the screw, the higher the vacuum. Idle is smooth. It also seems like there's a bog/stumble when I hit the gas to accelerate. Other than that, it seems to be running rich. Once past the little bog/stumble, it really runs nicely.

    My mechanical ability level is novice, but I'm trying. Ideas for where to start would be much appreciated!
    '78 Fairmont Box Top w/Straight 6/3-spd Manual Everything
    '81 Zephyr Wagon 4/4-spd
    '84 Mustang SVO 5.0 Swapped semi-junker (I didn't do it!)
    MAF, GT-40, BBK Shorties

  2. #2

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    Good for you doing it yourself! Was the engine up to operating temperature while adjusting the idle mixture? Give a try to putting the vacuum gauge in the toolbox (I never use one for idle mixture adjustment anymore... think I mighta once many years ago, lol...), and once the engine is up to thermostat/operating temperature, block the wheels very well and/or set the emergency brake on hard enough so that you KNOW the car will not move forward while idling in Drive (best to do both blocking wheels and emergency brake on), put the car in Drive, and turn on the fan to maximum and the headlights on and onto High Beam... while listening closely to the engine idle, adjust the idle speed to what it is supposed to be, and then slowly turn that idle mixture screw in until you hear the engine idle just begin to slow/roughen a wee bit (that's on the edge of being too lean), then turn the mixture screw back out 1/4-turn. Readjust the idle speed if necessary. The off-idle bog/stumble could be idle circuit related, or accelerator pump related. Readjust the idle speed and mixture as above, and take 'er for a spin. If bog/stumble is still there, Park it and see if there is a nice strong stream of fuel squirted in immediately when the throttle is moved off idle... bend a rod or adjust as necessary if there's any apparent slack at idle...
    Last edited by Walking-Tall; 07-16-2018 at 03:24 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  3. #3
    FEP Super Member erratic50's Avatar
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    Only other thing I can think of if the above advice (which is spot on imo) doesn’t resolve is possible double check float level. Too little fuel in the bowl yield too little fuel to the motor.... too much fuel in the bowl results in the opposite problem generally.

    Did you mess with anything during the rebuild or just give it a good cleaning and a carb kit?

  4. #4
    FEP Senior Member waggin's Avatar
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    Thanks, folks! I did a full rebuild and checked the float setting per gauge while it was apart. IIRC, I did do a minor adjustment to the float linkage (& maybe metering screw internally?) to bring it into spec. Other than that, it was an attempt at putting everything back together exactly as it was. Before I started, I had an even worse bog/stumble, and I expected that with the new accelerator pump diaphragm it would take care of it. It is much better after the rebuild, but I know it can be improved.

    Unfortunately, I can't put it in drive to set it up, as it's a stick. Idle is a bit high, so I'm going to dial that back, then try tweaking the accelerator pump linkage to give it a bigger shot, along with running the mixture screw back in a bit. It's a low-mile car that sat in the desert for decades, so there's no throttle blade linkage shaft wear/vacuum leaks. I'll also check the squirter operation.

    Eventually, this is going to get a 5.0 and a 5-speed, but I really want to make it run better as is first. If I'm successful, then I'll do all the suspension stuff first before the engine swap. A little success would be motivating!
    '78 Fairmont Box Top w/Straight 6/3-spd Manual Everything
    '81 Zephyr Wagon 4/4-spd
    '84 Mustang SVO 5.0 Swapped semi-junker (I didn't do it!)
    MAF, GT-40, BBK Shorties

  5. #5

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    Sorry, I missed that it is a manual in your signature. Is that ever cool!

    Okay, yeah, then the probable 600-700rpm in Neutral. Really needs to be nice and slow so you're certain it's only getting air:fuel from the idle circuit, that idle air:fuel mixture screw.

    By a long shot, not the fastest thing I've owned, but the '66 Fairlane sedan with the 200 and automatic that I once had was a very enjoyable car to drive... (after a driveway rebuild (stuck #1 rings from sitting a long time, fouling that spark plug about every 1000 miles... and a carburetor rebuild on the same/similar carburetor like you've done)) a surprising little bit of pep, and very nicely conservative on fuel use. Good luck with it, you'll get it
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  6. #6
    FEP Super Member xctasy's Avatar
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    Quote Originally Posted by waggin View Post
    Can someone give me a little direction in trying to tune my YFA carb? (1bbl carb on 1978 200ci I-6)

    I rebuilt it, then noticed when tuning the mixture screw for maximum vacuum, the farther out I turned the screw, the higher the vacuum. Idle is smooth. It also seems like there's a bog/stumble when I hit the gas to accelerate. Other than that, it seems to be running rich. Once past the little bog/stumble, it really runs nicely.

    My mechanical ability level is novice, but I'm trying. Ideas for where to start would be much appreciated!


    YFA is not a stock carb for the 1978 1-bbl 3.3 T code engine.


    It's a bolt on, but its got to be sourced from a 250 L code or 300 Big Six Truck, or a 1982-1988 Fox or Ranger, and there are a lot of differences.



    If you have the time, see these three posts.

    https://fordsix.com/viewtopic.php?f=1&t=77388
    Quote Originally Posted by xctasy
    My suggestion is to yse the Fox body 3.3 system, seen here in three version, each with the very common (non standard) Carter YFA 1-bbl carb off an F150 truck.

    On later carbs (post 1970, and certainly after 1973), they had a delicately balanced Purge CV ( Vapor Canister Purge Valve) which stole the BV, bowl vent vapors, vented the stuff to an activated carbon canister. There were Delay Check Valves to sort out reducing surges. Any problem with the grommet or PCV, and the carb would surge like a B -tard.






    Element 1: Lower Line to under the carb. EV89 PCV valve on the Fox body rocker cover puts the oil filler at the back.

    The PCV valve hookes to a 3/8" grommet, and the line goes under the carb on an adaptor like this





    The lower manifold BSP bolt (also used for the power brake booster) can be used as a last resort if its head is 1960-1979. The later 80-83 heads are like the ones above. I'd personally use the stock adaptor.

    Element 2: Upper line from a sealed oil filler cap


    This goes to the air cleaner with a felt junction

    A better view



    If you grab the 1976 onwards racker covers, they are baffelled so you don't get oil-throughs.



    a 66 will run and take the later fittings very easily. Its simple, and will do the job.

    The earlier diagrams for PCV routing, see Stormin'Norman's Electrical and Vacuum Trouble Shooting (EVTM) and Vhecile Emission Control Information (VECI) diagrams for Clean Air Act Fords from 1965 to 1968.

    Quote Originally Posted by Stormin' Norman
    [Alldata's VECI labels only go back to 1982, AutoZone's for the 1978-1979 Fairmont use a lot of 2.3 - 4 banger diagrams.

    BUT this document gives all the basic diagrams and the best Non-Geek Speak explanation of every emissions system device known UP TO 1968.

    PLUS, it gives complete and clear VACUUM Issues Diagnosis for all the I6 and V8 engines, both for Manual and Automatic transmissions from the 170 CID and up to the 300 CID sixes and all the SBF and BBF V8s.

    Its kinda like that book, "Everything You Wanted To Know About He-ing and She-ing", only the pictures are in black in white!

    http://www.mustangtek.com/Library6/V...Book-5000.html

    The basic VECI Diagrams start at page 31 but the details on them start on page 29.

    And while you're there, check out the other menus as well as all the Ford TECH and Sales books. Most are in PDF format.

    http://www.mustangtek.com/LibraryFordTech.html

    http://www.mustangtek.com/index.html

    I found the site looking for VECI diagrams using the part number on an old label.
    Your conversion is exactly like Frankenstang's https://fordsix.com/viewtopic.php?f=...562727#p562727


    and Asa's. https://fordsix.com/viewtopic.php?f=1&t=76871 and https://fordsix.com/viewtopic.php?f=1&t=76774


    All tuning problems with YFA's are just PCV, ignition and metering rod "needle" and jet specification settings. There is a little in the rebuilding process, and about 85% of all rebuilt YFA carbs are in fact wrong for a 3.3 i6 Fox, but don't let that stop you. Its a nice carb.

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