Old Tractor Carb adjustment

Discussion in 'Shop Talk' started by mary,tx, Oct 31, 2004.

  1. mary,tx

    mary,tx Well-Known Member Supporter

    Dec 4, 2002
    I have an old Ford 850 tractor I recently purchased. The previous owner converted it from LP to Gasoline and used a Zenith Carb. The parts house had that carb listed for an Allis Chamblers tractor.

    I put in a new carb kit as best as I could and need to know what to do next. There are two adjustments, but I do not know the steps/process to make necessary adjustments. Slow idle the tractor seems to run, but when I turn up the throttle, it dies out.

    I put in the kit since the tractor would sputter and lose power when I tried to use the shredder. It also had a pretty bad fuel leak around the gasket where the two parts of the carb come together. At least there is no leak now, but it doesn't run quite as well as when I started. :(

    Dale (dh of mary, tx)
  2. rambler

    rambler Well-Known Member Supporter

    Jan 20, 2004
    How far out do you have the main needle? I think 2 full turns out is a starting point, but I forget... Anyhow sounds like you need it turned out farther. You can do this while running, see if it smoothes out.

    When turning it in, do not bottom it out very hard. Be gentle with that.

    It is possible some gunk is stuck in there yet, that happens after a rebuild, some stray dirt floats into the needle & messes it up.


  3. John Hill

    John Hill Grand Master

    May 12, 2002
    New Zealand
    This is bit of a hard one Dale without more information but I will stick my neck out. :) This is for a very simple type of carb.

    You say it idles OK dies when the throttle is opened. There are quite likely two distinct 'carbs' in one, the tiny little fixed jet one that does the idle and the main power system. There is possibly a small screw that adjusts the amount of air that is mixed with fuel while idling. Identify this if you can and for the moment leave alone.

    The other adjustment may be the one that controls the amount of fuel that is used during the power phase.

    Can you open the throttle just a little until the engine starts to stumble and hold it there? With the engine idling screw the main power adjustment in as far as it will go without forcing things, count the number of turns so you can restore it if necessary. Now slowly open the throttle until you get to that stumble stage, slowly screw the big screw out and see if the engine smooths out, if it does then open the throttle a little more and if it stumbles again repeat the process.

    I hope someone can give you better advice but if not I hope this helps you out.
  4. moopups

    moopups In Remembrance

    May 12, 2002
    In beautiful downtown Sticks, near Belleview, Fl.
    All carbs, worldwide, are designed to run at 1 and 1/2 open from soft bottoming.
  5. unioncreek

    unioncreek Well-Known Member Supporter

    Jun 18, 2002
    SE Washington
    I don't know whether the carb has two adjustment screws one for idle the other for full throttle. The only way to find out is start turning screws. Try adjusting one if the idle increases it is probably the idle ajustment screw, but if it wants to quit or runs funny turn it back. Make a point to record how many turns or part of turn you do. If there is another screw turn it counterclockwise a little and open the throttle almost full open. Then keep turning that screw counter clockwise until it runs evenly, if it starts to stumble and run funny turn it back until it runs smooth.

  6. rutter

    rutter Member

    May 12, 2002
    Turn load jet to bottom, turn out approx 1-3/4 turns start, run at fast idle for a few minutes. adjust open until engine starts to loose power, turn in until even run. Then check under load adjust using minor movement to give full power.

    Be sure prior to starting this that engine is at operating temp. further it does no good to adjust if timing, points etc are not in good working order. From your previuos description I would also check the condenser, many times this has proven to be the problem, rather then the carb it will give same syptoms . especially if it runs at idle ok.