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  • OT, tractor Carb problem

    Need to get help with adjustments to a carb on a MF135. It is a '73 or '74 gas with a Zenith #013338 carb. Was bush hogging earlier this fall and could just keep pto at 540-560 rpms, engine maxed out at 2000 rpms. Things got worse and inspection found the sediment bowl screen covered in rust and the bowl about 1/2 full of sediment. The filter at the carb was also full of rust. Managed to break of the brass elbow the filter was screwed into, so had to remove the carb to get the broken part out. Got a carb rebuild kit to get replacement gaskets. Cleaned the carb thouroughly, and replaced the float shaft and the brass seat and needle that is operated by the float. Left the other jets and components alone. Just got it back on and started. The engine revs to over 2500 rpms and the throttle will not slow it down. I re-checked the linkage and it is hooked up properly. The throttle butterfly was not removed while torn down, so it should be OK. The choke linkage also works as it should. I tried closing down the screw(needle valve) just below the throttle shaft and that had no effect.

    I have a little experience working with engines, but need guidance.

    This is my Dad's tractor but he is in a rest home with Alzhiemers and was not any better at mechanic-ing than me. I have the operator's manual but it is no help.

    Thanks in advance for any help you can give.
    North Central Arkansas

  • #2
    90% odds the throttle butterfly is stuck partly open. Disconnect the linkage and see if the butterfly shaft lever moves freely and closes firmly against the idle stop. You may have to remove the carb to look at the butterfly. It should close to within maybe 1/16" at the widest part of the gap.

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    • #3
      MF vs Ford

      I am not sure on your MF but could the spring that pulls the lever back on the govenor have slipped off? Vaguely remember my 8N having a spring that pulled the lever back on the govenor that ran the throttle. Jan

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      • #4
        I'll check it tomorrow.
        North Central Arkansas

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        • #5
          If you're going to continue working on that tractor, get an I&T shop manual for it. While not as comprehensive as an official factory service manual, they're usually good enough and inexpensive to boot. Places like Tractor Supply carry them (or used to!), or you can order here: http://www.tractorpartsinc.com/servi..._2937_prd1.htm Price is only $33.00.

          The governor linkage has a spring that pulls the throttle open; the governor closes the throttle. Operate the throttle (speed control) lever from idle to WOT and observe the throttle on the carburator. It should be closed at "Idle", and go wide-open long before the speed lever is full-on. Do this with the engine Off!

          Make sure you have your hand on the ignition switch when you try it, don't let the engine over-rev.

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          • #6
            Look for a vacuum leak!!!

            THANX RICH

            People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!
            People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!

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            • #7
              ulav8r: I have the same tractor. 3 cylinder GAS Perkins with zenith carb. hav not checked the carb number. I have the full service manual from MF. If I can copy and send you a few pages by email let me know.
              John Burchett
              in Byng OK

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              • #8
                I too would be checking the linkages from the governor, and the way they connect to the carb. Normally the hand throttle does not connect to the carb at all. The hand throttle simply changes the governor's spring pressure.

                So I would be looking to see what happens when you open the throttle lever wide (engine off), it should increase the force from the governor holding the throttle open. Is it possible to get the linkage, or the arm on the throttle shaft, mixed up (upside down?) so it it doing the opposite of this?

                If the short arm on the butterfly shaft had been removed, I would check that first probably.

                Note: I have not seen one of these tractors, just taking a guess based on other engines.
                Last edited by Peter S; 12-11-2010, 10:47 PM.

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                • #9
                  I think the others are on the right track, sounds like you have something fouled up on the governor spring or linkage.
                  James

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                  • #10
                    Thanks all. Email sent to kc5ezc.
                    North Central Arkansas

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                    • #11
                      Checked the governor linkage, seemed to be OK. By leaving the choke on, I ran it long enough to to get the bush hog hooked up and in the barn. I will get back to it later. I am three hours away so can't work on it every day.

                      Will probably tear the carb down again, should I use some kind of sealant on the gaskets?

                      Looked at changing the spark plugs and could only see one of them. Looks like the exhaust manifold or the gas tank will have to be removed to get to the rear three plugs. Will also have to find a 7/8 plug socket.
                      North Central Arkansas

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                      • #12
                        Disconnect the fuel line at the carb, then turn on the gas valve. Have a coffee can or something under the end of the line while you check to see that you have a good flow of fuel out of the line.

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                        • #13
                          Mark the throttle at totally closed position and verify that its staying there whilst operating --- its real simple, you either have an improperly assembled governor and or linkage/springs OR you have a massive vacuum leak,

                          engines need two things to run past idle - more fuel AND air, so unless your using some kind of anaerobic fuel look for a place where its getting more air - I suspect your throttle plate is cracking open some as it would not take much at all -- I suspect this more than the other due to the plate compensating for fuel air mixture due to the airflow having to go past the carb venturi,
                          A vacuum leak elsewhere will most likely result in a mixture too lean to run @ that kind of RPM without falling on its face...

                          Need to add; You could reassemble the carb and governor linkage to the T - exactly the way you took it off and it could still be the problemo,,, carbs (esp. from that era) mounted on very loose fitting bolt holes that can totally change the governor's linkage function too them -- every time a carb is removed and put back on the governor should be re-calibrated...
                          Last edited by A.K. Boomer; 12-13-2010, 10:30 AM.

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                          • #14
                            Carb gaskets don't need sealant if they are new from a kit, I have added a little between carb and manifold if reusing an old gasket. Since you rechecked and are sure that springs and linkages right, I would bet on a bad vacuum leak somwhere, either between the carb and manifold or elsewhere. Running with choke on is probably cutting down the extra intake air enough to limp it into the barn.
                            James

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                            • #15
                              OT, tractor Carb problem

                              Sometimes the hole in the carb body where the shaft pivots gets worn oversize and this lets air enter the venturi and causes the engine to rev. I have had this to happen on older engines. This can be repaired by oversizing the shaft hole and installing a bushing. ....Jim

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