Mountfield Mower Help

[groovynooby]

Hi All,

I've recently acquired an RV150 engined, Mountfield SP534, I bought it cheap knowing it had an issue as the previous owner said he hit a tree and a spring popped but as the mower started first time I took it on for £25.

Anyway, I first used the mower and it appeared to be running at full choke and It had zero rev adjustment using the throttle control (the adjuster moves but the revs don't change, no idle just full tilt) so I had a look and tried to diagnose the fault using various videos and web resources.

On looking it became clear that the governor flap was snapped in half so I bought a new flap, spring and link and installed today, I've just used it and it cut the grass well but the throttle control is still wrong; the engine appears to rev 100% at all settings apart from when the throttle control is pulled right back towards the handle bars, I've checked the adjuster is working correctly in that it moves the gubbins on top of the carb as it should and it does so now I'm stumped??

In addition, I don't know if this is relevant, but on stopping the engine often gives a little backfire.

I'm not very mechanically minded and I've never attempted to fix anything like a petrol mower before so any help or thoughts would most gratefully recieved.

Thanks,

Groovy

 

[Nige F]

IF it`s a Briggs and Stratton engine - it prob. needs a new carb. diaphragm Loadsa videos online show how it`s done

 

[Burnerman]

If the engine is on full choke, it will be chuffing black smoke and not running happily at all.....check the air filter for oil or dirt.
Can you move the lever on the top of the carb so that it closes on to the throttle stop screw? If it slows up then, its a governor issue.
Please bear in mind, if this is not a self propelled machine, the engine revs are always constant, and the throttle lever has generally little effect!
Ignore the backfire - thats the engine sucking fuel in, which gets ignited by the hot exhaust rather than the spark plug.
John

 

[groovynooby]

IF it`s a Briggs and Stratton engine - it prob. needs a new carb. diaphragm Loadsa videos online show how it`s done

Unfortunately it's not a Briggs and Stratton it's a Chinese offering I believe.

If the engine is on full choke, it will be chuffing black smoke and not running happily at all.....check the air filter for oil or dirt.
Can you move the lever on the top of the carb so that it closes on to the throttle stop screw? If it slows up then, its a governor issue.
Please bear in mind, if this is not a self propelled machine, the engine revs are always constant, and the throttle lever has generally little effect!
Ignore the backfire - thats the engine sucking fuel in, which gets ignited by the hot exhaust rather than the spark plug.
John

Well, I've used the mower again and it does appear to work ok, there's no black smoke, it's starts on the 2nd pull and happily runs without issue it's just very noisy compared to my previous mower, it is self-propelled but the revs seem pretty constant... Perhaps everything is as it should be, I don't quite think so but I think I will carry on and use it... 'twas a bargain for £25!

Thank you both for your help.

Groovy

 

[Extreamskier]

So I had this same issue and followed the movi by control rod to the front. It ran better with a little extra throttle or reduced air flow.

I played with the black ‘half moon’ grub screw in the bottom photo till it stopped bottoming out. Seems to work well now.