Mountfield RSCT 100 rotavator carb question

Discussion in 'Engineers' Talk' started by Garagefairy, May 8, 2022.

  1. Garagefairy

    Garagefairy New Member

    Good day everyone. I hope someone can advise me. I have a Mountfield Manor rotavator (the small one) fitted with a Mountfield RSCT 100 engine. Not very old not much use, maybe an hour a year for the past 5 years. Starts first pull is normal. But after allowing a little time to warm up and then easing the throttle down toward the 'fast' position the engine hesitates and can almost stop. Returning to 'start' and engine picks up again. Unit is quite useable in this condition although there is some hesitancy on rough ground.
    I am pretty sure I should be able to move throttle to fast then slow then slower before stopping the engine but this seems not to be the case. I have not fiddled with the carb controls but did find a small lever with a light spring which I could move a tad, whereupon engine speed became much faster and ran quite happily ... I assumed this was a governor system?? I have failed to find an adequate picture of this carb and from googling I think it could be one of two units. I am not afraid of delving inside if I am aware of what I am doing and what to look for.
    Can anyone give advice, please? I have found posts concerning lawnmowers but am not sure if the carbs would be the same??
    Thanks, Phil
     
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    The main jet in the carb is partially blocked by a small piece of dirt. Drain or turn off the petrol, remove the float bowl on the bottom of the carb, 1 10mm nut I suspect. The main jet is located in the tube that dips down into the float bowl and also serves as the anchor for the 10mm bowl fixing nut. Use a flat screwdriver with a 4mm blade to unscrew the jet, look through the small hole in the jet to check for blockage. Blow through the jet from the top side to clear the hole.
     
  3. Garagefairy

    Garagefairy New Member

    Thank you. I will do as you suggest as soon as I can ...

    Cheers, Phil
     
  4. Garagefairy

    Garagefairy New Member

    Hello again. I removed the carb this afternoon and cleaned / sprayed the unit with 'carb spray' including removing the float chamber and the jet in the tube and the float / valve.
    I am afraid it made no difference... indeed I repeated the clean up; I found everything to be quite clean.
    Once again, the engine started first pull on 'start' with the air intake vale fully closed but when opening the valve with the throttle moving a little towards 'fast' the engine started to 'hunt' and if the control was moved further towards 'fast' the engine would stop.
    This is a puzzle. If I push the governor rod a bit then the engine speed increases nicely but this action makes no impression on the air intake valve.
    Any ideas?? I looked for adjustments but failed to find any apart from the choke/air butterfly on the throttle unit and that seems OK.
    I did notice that the seal on the float chamber (about 53mm id x 2mm cs) was not pristine but as there are no leaks I guess it is sealing OK ... I did try to find a carb gasket / seal kit but failed miserably. One difficulty was finding out what unit I had as the RSCT 100 engine and carburretor yield few, if any results. I did find out that the 'article number' is important. mine is: 211360063 / M13 but a fellow I spoke to at a spares shop failed to find details of the carb seals apart from the gasket between carb and engine block. I believe M13 gives the Mountfield Mano rotavator. Why do they make life so difficult?
    At the moment I am back together and running on full choke ... I expected this alone to cause hunting as the engine warmed up but it does not. As above, I am puzzled but will continue.
    But... all ideas welcome.
    cheers, Phil
     
  5. Bob Rathbone

    Bob Rathbone Screwfix Select

    The symptoms suggest fuel starvation, do you have a good supply of fuel into the float chamber, is the fuel stale or new.
     
  6. Garagefairy

    Garagefairy New Member

    Thanks to everyone for suggestions. Fuel is new and unit is kept over winter without fuel.
    After more searching I have found an exploded diagram of the Manor Rotavator that has parts numbers on it. Yippee. So before I delve further I have ordered a new fuel filter and carb gasket set. It seemed impossible to find the carb float chamber O ring seal as a specific item so will replace it with an O ring (BS033 I think is correct).
    I also found a service manual for the engine and carb which gives info on various adjustments so will make sure it all fits to spec.
    These parts should be with me by the end of the week so if it is fine and dry Sunday or Monday, I will fit them.
    Once again, thanks for the encouragement.
    Cheers, Phil
     
  7. MRY

    MRY Screwfix Select

    Is there a possibility that some spring or linkage has sprung or become unlinked?
     
  8. Garagefairy

    Garagefairy New Member

    Nothing loose but ... maybe later than expected I think it is fixed.

    My expectation is that it was fuel starvation caused by a partially blocked main jet that feeds the float chamber. I had unscrewed the jet in the central pillar and, I thought, cleaned out the main jet (?? about 3cm long small bore perforated tube that sits under the jet you unscrew). But obviously not as I could now see a bit of debris in the jet passage.
    All back together with new fuel filter and carb gaskets and away we go ... I hope.
    Thank you to all for encouragement and suggestions. I will be wiser next time.
    Fues drained now until unit is used again.
    Cheers, Phil
     

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