mountfield lawn mower sp480t engine hunting?

just fixed my rs100 mountfield from hunting revs remove carb
remove plastic idle screw remove black plastic plug which was located under screw and found small O ring had broken off .through O ring fit plug without O ring .jobs a good one

eric
September 2017

Hi all
Mower was working fine, then ran out of petrol. I filled it up but it wn't start now. Any ideas?
Thanks in advance of any advice

colin
July 2014

Your problem is the diaphragm in the carburettor. Purchase kit number 795083 from any Briggs and Stratton agent. It consists of a new diaphragm and gasket. The diaphragm is located between the carb base and the top of the fuel tank. You will need to remove the tank and carb as one unit and then remove the five carb retaining screws to the tank. LIft off the carb, remove old diaphragm and gasket and replace with new (diaphragm goes on first, then gasket) equally re-tighten the five screws and refit carb/tank assmeble. Clean out air filter and test. Should be fine.

Pleasant
September 2011

Quick update.

Apparently the spring is called a Governor Spring and I found them on ebay here:

http://www.ebay.co.uk/itm/BRIGGS-CLASSIC-GOVERNOR-SPRINGS-MOUNTFIELD-HAYTER-/110732171024?pt=UK_Home_Garden_GardenPowerTools_CA&hash=item19c826d710

walker-14
September 2011

I have the same mower / same problem.

On my mower it's caused by a spring that regulates the engine speed. The spring has lost all of its 'spring' and isn't doing its job properly. I tried to shorten it to give it a bit more spring and that worked for a while, but the spring is so short now that there's no adjustment left.

If you take the top plastic cover off the engine, then remove the air filter assembly the offending spring is underneath. You can't miss it.

Run the mower without the air filter fitted and you will see the little regulator arm swinging backwards and forwards in step with the engine revs. The spring is supposed to open the throttle a little more when the rotor shaft is under load and slowing down.

With a slack spring, the engine constantly goes from high revs to almost stalling then back again. I assume that this sounds like the problem you're having

Now that I have found the problem, my next challenge is to find a replacement. I usually find things in less than 30 minutes with google, but I've already spent about an hour and no luck so far. If you find one please let me know.

walker-14
September 2011

Could be fuel mixture adjustment screw needs adjusting while the engine is running. Is the air filter clean ?

davidj
September 2011