Mountfield RS100 Running Flat out

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Glencmp
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Mountfield RS100 Running Flat out

Hi ;) Its been a while :) My Neighbour has a Mountfield RS100, Not that old, but when he starts it runs flat out, Ive checked the springs etc and everything seems fine, is there anything I can check for him?

 

Cheers

Glen

wristpin
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A bit modern for me but is it

A bit modern for me but is it one with a fixed throttle  - no lever on the handle bar and intended to always run at a fixed governed speed.?

hortimech
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Never had much to do with

Never had much to do with these, but it sounds like a governor problem. Is something jamming the linkage (yes, I know you said you checked the springs), does the linkage move freely when the engine isn't running ? Is the clamp on the end of the governor arm loose ? Is the governor set correctly ?

Failing a linkage problem, something could have gone wrong inside the engine, the weights could have fallen of the governor gear. the gear could have stripped its teeth, etc.

 

Glencmp
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Hi ;) So The linkage is free,

Hi ;) So The linkage is free, no apparent problems there. So when you start the mower the lever moves in to the flat out position, if you move the lever forward it goes to Idle and idles great, but let it go and it springs straight into Flat out mode. I have a horrible feeling its inside the mower, but im hoping it might be fixable outside the mower. Nothing looks missing. 

Cheers

Guys :) 

Glen

He who Cuts Last, Cuts Longest!!

hortimech
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It should do the opposite,

It should do the opposite, when the engine starts, the governor should try to shut the engine down and the spring should try to open it up again. it is the balance between the governor and the spring that sets the maximum revs.

Has anybody removed the carb for any reason ? They may have refitted it incorrectly.

You could try resetting the governor if everything is in the right place. at the bottom of the governor arm there should be a clamp bolt, slacken this, move the arm so the throttle is fully open on the carb, noticing which direction this is. now turn the shaft that sticks out of the engine, the one that the arm is normally clamped to, turn it in the same direction as you turned the arm to open the throttle, it should come to a stop. At this point, with the throttle fully open, hold everything in place and tighten the clamp bolt.

Now test run the engine.

 

wristpin
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You havn't  answered my

You havn't  answered my question re the throttle control.

If it is a "recent mower" with a fixed throttle  - that is no handlebar speed control (not to be confused with the Operator Presence Control which has to be held to keep the engine running - it will always run at its pre-determined govern speed - no slow run or idle . 

As described by Hortimech the governor will attempt to slow it down but in the case of a fixed throttle machine that will only be to its governed operating speed  - probably about 2800 rpm .

EDIT Just looked at an image of an RS100 on that well known auction site and there is no throttle control .

Also found this

http://www.servicelink.org.uk/sites/default/files/Manuals/0d0444af.pdf

No throttle control just a bulb primer for starting.

That confirms that it has a fixed throttle and will only run at its governed working speed, so that will be the slowest that it will run. Possibly what you describe as "flat out".

.

Glencmp
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Thanks Guys, Im a little

Thanks Guys, Im a little protective of Motors running flat out, but this really is flat out!!!! Ill have a look at the Manual you've provided and see if I can figure this out, and yes its a fixed Throttle with no control, my Neighbour was using the Brake to control the speed of the engine, So I could be wrong, its meant to run that way but its hell of a fast!!

ThanKs Guys

Glen

He who Cuts Last, Cuts Longest!!

wristpin
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Neighbour was using the Brake

Neighbour was using the Brake to control the speed of the engine,

Not really sure how he could do that as releasing the "brake" (OPC bar) first kills the ignition and then applies a brake block or band to the flywheel. 

Glencmp
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I thought it was weird but he

I thought it was weird but he shown me how he did it and it works.

He did get in contact with Mountfield and they said it looks like he has chucked the weights of the Governer :( Thats an expensive bill :( 

He who Cuts Last, Cuts Longest!!

hortimech
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If the weights have come off

If the weights have come off the governor gear, it could be cheaper to fix it now, than to wait until the engine gets damaged. If the bits are floating about inside the engine, then they could get jammed up in anything, this includes the piston/bore. If this happens, then it will probably be cheaper to buy a new mower.

It will probably be easy to fix, remove engine, remove sump, check for damage and if okay, remove debris, remove old governor gear and replace with new one. Fit new sump gasket and refit sump. re-adjust Governor, refit engine and test run. This will undoubtedly be cheaper than a new mower.

wristpin
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Has anyone actually put a

Has anyone actually put a tachometer on it to see what “ flat out” is ? Just might save unnecessary dismantling etc.