Mountfield Manor Rotavator issue advice please.

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Phil Russell

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This is puzzling me and I know it is not necessarily apt for this forum but information is very scarce:
I have a Mountfield Manor cultivator, a small model suited to garden and small allotment use. It is about 6 years old. Fitted with a RTSC 100 engine.
Symptoms of fault: Engine starts perfectly on first pull, control on 'start' which closes the choke butterfly. But, even after a few minutes running and with engine hot if I attempt to move throttle control from choke to 'fast' the engine hesitates / hunts and can stop unless I move back to choke. I have cleaned out the carb float chamber and float needle valve and quirted carb cleaner in every orifice I can find. I have done this twice and it all looks sqeaky clean. As far as I can see, the throttle cable is adjusted OK i.e. in 'start' the butterfly is closed. If I twiddle the governor rod/spring then engine revs can increase markedly without movement of the butterfly.
Air filter is fine ... problem happens without filter.
Any ideas anyone? I can use the machine as it is and it runs happily on full choke and I can cultivate that way. But it niggles me as it is clearly not right.
All help appreciated. I am not aware of any adjustable jets.........
Cheers, Phil
 

Jameshow

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Might be worth posting on arbotech forum where they will have greater knowledge of small petrol engines??
 

Sandyn

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sounds like a fuel problem. Depending on the engine design, some things which are unlikely, but worth a check.
Needle valve sticking?
Filter on petrol line inside the tank blocked. There is often a nylon or sintered filter in the tank.
Does it have a priming pump, can you see fuel being pumped to the carb and returned to tank
E10 petrol causing gum formation in petrol lines.
Some carbs have complicated rubber gaskets inside which might have a tiny hole/crack. somewhere.
You have cleaned the carb, did you completely strip it down. There are sometimes little chambers inside the carb which can accumulate rubbish and cause problems.
Faulty fuel line from the tank/in the tank, they can deteriorate and fold causing blockage.
 

Phil Russell

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Thanks to everyone for suggestions. Fuel is new and unit is kept over winter without fuel. No priming pump. Carb stripped as far as I can see is possible.
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
 

MikeK

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If the engine runs fine with the choke closed, but starts to stall as soon as you open the choke, then it could be lean mixture (too much air and not enough fuel). You could have a crack somewhere in the carburetor body that lets too much air past the venturi or a main jet is clogged not letting enough fuel into the mix.
 

Housey210

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Any vacuum pipes? simular issue on a moped, turned out to be pin holed rubber pipe.
 

Fergie 307

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Does sound like a blocked jet or similar. Also have you checked the air filter? If it's the type that should be oiled and it is dry than it can allow too much air through, leading to lean running, being compensated for by the choke. Shouldn't cause as extreme symptoms as you have, but still worth a check. They also sometimes disintegrate, so you effectively have no filter, which can also cause lean running. And what does the plug look like? Should be a digestive biscuit brown colour of its running the right mixture. Black and sooty, too rich. Very pale or white, too lean. And have you checked the plug is the correct one and in good shape with the right gap. Worth checking these things just in case. If you don't use it often then I would either empty the tank and run it till it stops to empty the carb of petrol before storage, or use a fuel additive. Unleaded is awful stuff and will deteriorate rapidly in storage, even in just a few months.
 

imageel

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I concur with others - this is most likely a blocked idle jet most likely caused through the use of E10 - fuel with 10% ethanol in it. This stuff degrades over time and can gum up small jets - like the idle jet.
I had this happened to me on my small Honda Izzy which would start from cold fine, then start hunting as soon as the choke opened up when warm and the fix was to strip the carb and leave overnight in an ultrasonic bath to clean it.
Subsequently I always use a fuel additive, Briggs & Stratton - one which was the cheapest I could find and have not had a problem since.
This problem is more common with the smaller capacity engines because they have the smallest jets.
 

Fergie 307

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Apologies if someone has already said it but acetone is ideal for removing varnish like deposits from the jets or carb body, and blow them through with an airline or airduster.
 

Blister

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Time to buy a new carb , I assume you have used compressed air and blown through all the drillings
 

clogs

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having fixed many a mower etc...used to do it for a living......I decided to buy my own Ultra sonic cleaner, esp sinc this [email protected] fuel u get now......
sometimes taking a couple of goes to clean out the gunge.....
only once did I need to buy a new carb for a job.....
The carb - prob Chinese can be had with prices starting from £12'ish depending on type.....
Cant remember a carb being made anywhere else otherthan Japan....Honda etc.....
Carb cleaner spray does very little now as they have changed the ingredients.....
the old stuff was/had a mild acid.....
 

Phil Russell

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Hopefully all sorted:
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) previously by multiple bursts with carb cleaner. 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.
Fuel is drained now until unit is used again.
Cheers and thanks to all,
Phil
 

Blister

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Hopefully all sorted:
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) previously by multiple bursts with carb cleaner. 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.
Fuel is drained now until unit is used again.
Cheers and thanks to all,
Phil
That is probably called an emulsion tube , good job reviving the unit
 

Torx

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Hopefully all sorted:
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) previously by multiple bursts with carb cleaner. 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.
Fuel is drained now until unit is used again.
Cheers and thanks to all,
Phil

Late to the show, but…hopefully? As in, you didn’t try it?

I’d have suggested the mechanism is incorrectly assembled and you were choking it in the fast position, have a mountfield mower that’s been like that for 10 years, used weekly in the dry months.
 

woodieallen

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Hopefully all sorted:
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) previously by multiple bursts with carb cleaner. 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.
Fuel is drained now until unit is used again.
Cheers and thanks to all,
Phil
If you use Aspen fuel at the last fill up then you don't need to drain it.
 
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