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Collection, Preservation and Display of Old Lawn Mowers

1973 Mountfield M3, Briggs and Stratton engine

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I am Delighted to join the club. I got this from my father, it is a little over 50 years young… it ran perfect for all those years only for one or two little fixes. It started idling high a few days ago and my father tried a few things and eventually ended up replacing the carburettor but no better. He just happened to come across another lawnmower free from my brother so he gave me the M3. I still believe lol.
I have some perplexing issues (to me) around this lawnmower.                     I’ve done my upmost to check and get some clarification on things  before posting here, as I dont like messing about. But I seem to just meet a dead end.
I’m hoping someone would be kind enough to tell me: WAS the original engine for the Mountfield M3, a briggs and Stratton engine? and if so is there any way to know if it’s the original engine that was on the body when it came out of factory?

How hard is it to get parts for this, for example, grass box?

I’d lov to restore it for my fathers sake  and it has sentimental value to me as my first introduction to an engine! 
I’ll include some pictures with information 


thanks so much

kind regards 




wristpin Thu, 23/05/2024

Engine parts should be fairly readily available but chassis parts will be hard to come by - particularly a grass box. An image or two of the top of the engine with the blower housing (cowling) removed showing the carburettor, throttle and governor linkage will be useful, particularly with the original and new carburettors installed.

ronanpw Thu, 23/05/2024



Hi, thanks for your reply, here are some pictures. I havent got the old carb yet and I'd be apprehensive about swapping them over so hopefully these pictures will help.



olcadmin Fri, 24/05/2024

Thanks wristpin - ronanpw has added the images correctly but there seems to be a new glitch on the site which means they are not appearing. I will check and put right if possible. 

wristpin Fri, 24/05/2024

The governor spring has been stretched to the extent that it will never work properly and I notice that the throttle stop screw is fully screwed in. That aside it’s difficult to work at a distance !
If its any help, I attach a couple of images of a similar set up on my 1972 Hayterette , a non running  rescue that does the rough stuff a couple of times a year.











ronanpw Fri, 24/05/2024

Hi, wristpin, thanks very much for that. I appreciate it. I’ve adjusted the throttle stop. Would it be difficult to get another governor spring? This one’s for the bin but I will keep it for reference 

wristpin Fri, 24/05/2024

Probably. Different springs for different applications. Post the BS Model, Type and Code numbers that are stamped in cowling and I’ll find you the specific part number for your machine. 

ronanpw Fri, 24/05/2024

Apologies… you’ve stated engine parts shouldn’t be too hard to find. 
Is there a particularly unusual way of attaching these types of governor springs.

From what I can see from another mower, it’s just a ring on each end of the spring. How to get this attached baffles me. Any advice much appreciated 

ronanpw Fri, 24/05/2024

Thanks, very much!!

Model 92908 Type 1344-01 


so on the case it looks like.          
 92908 134401 73082808

thanks again 




wristpin Sat, 25/05/2024

I’ll sort out the part number this evening . There is a procedure for fitting it that’s actually shown in the BS manual. I’ll copy and post it later. 

ronanpw Sat, 01/06/2024

Hi again I’m picking up the replacement governor spring today.
Fingers crossed… Where would I get my hands on a BS manual relevant to my lawnmower? 

wristpin Sat, 01/06/2024

The BS manuals are specific to the engine model and production date not the mower to which they are fitted. That page was from the 1975Repair Instructions 1V which has, to a great extent, been replaced by the CE8069 Repairman’s Hand Book (1919- 1981) .  Possibly the post 1981 Single Cylinder L Head ( aka side valve) manual will be of more use. 
Manuals may be ordered from a Briggs and Stratton agent or, possibly , from Amazon. 

ronanpw Sat, 01/06/2024

Hi again. So I fitted the governor spring correctly… But it’s not moving the arm it’s attached to closest to the engine. When I turn throttle on, the governor spring seems to do what it’s meant to do but it is not moving the arm controlling (air? Think that’s right?)

any advice most welcome 


ronanpw Sat, 01/06/2024

Thanks so much wristpin.
I’ll be back later with some better details and some photos of the carburettor 

ronanpw Sun, 02/06/2024

stationary mechanism

This part will not move back and forth at all when turn throttle is on or off, Im no expert but it seems to be catching on something

new governor spring throttle off

New governor spring. Throttle OFF, doesnt look quite right (to me) incorrect carb??

its the correct spring





Side throttle on side side view


front view

front view

wristpin Sun, 02/06/2024

Looks like you havnt got the governor spring quite right at the link end. Seems to be hooked to the far side of the link loop. Also in one of your images the spring is being pulled round the inlet  - will end up with a distorted spring. 
in passing, you also seem to have the tin shield comes from under the cylinder outside the blower housing - should be tucked inside.

If I get a moment tomorrow I will take the top off my old Hayterette and try to pose the linkage as it should be. Not a lot more I can do.


wristpin Wed, 05/06/2024

Two issues. One that you’ve got part of the air duct  X from under the cylinder that should be tucked inside the top cowling jamming  up the throttle spindle. Second , looks like despite the instructions you have possibly got  the governor spring incorrectly fitted . Should not be under any tension when relaxed , neither twisted or stretched. Carefully remove it and reassemble it strictly as per the instruction sheet. 

ronanpw Tue, 11/06/2024

Hi wristpin. Thanks for your help and sorry for delay in reply, as I couldn’t quite grasp the details of the action.

as it turned out the linkage was bent/broken, diaphragm was torn and perished and the air filter was too restrictive [not a genuine and or suitable] briggs and Stratton part.

It is now running smoothly.
Thanks again for your help, I have acquired two of the most relevant manuals as suggested. The single cylinder L head and the CE8069 repair man’s handbook