I have a 1976 Mountfield M1 rotovator 3.5hp Briggs & Sratton Engine.
It starts first pull with or without choke and bellows out thick black smoke.
i have changed the oil, and petrol, spark plug, air filter & points & have also cleaned the carb with carb cleaner and airline.
the carb diaphram is not split or brittle, carb filters are all clean. There is no dirt in fueltank .
It does rev up and run but smokes and hunts on idle,
i have been on the briggs and stratton web site and they dont have a book for this age model ,
Model number 92902 1328-01 76121702.
i know it is a modle 92902 was made in Dec 17 1976 production line number 02.


How do i ajust the carb to make it run right or is there more problems with this enigine?

Neil, April 2008

hi the problem may be that the valves are blowing and that they need reseating ? try regrinding the valves with grinding paste so the seat and seal correctly.the black smoke is caused when u have a leaky valve seat and you may need a new head gasket or some gasket sealer too regards paul
ps do you have a service manual for this model as i have one too and i have serviced mine but need to set the points up and need the gap info can you help thanx

paul, March 2010

google a bit harder for a b&s maintenance manual.
I downloaded one last weekend for my old M1 and have now done my annual till.
9379684-How-To-Repair-Briggs-Stratton-Engines.pdf

johannes, March 2010

To me it sounds as though the rings are getting worn. Oil is leaking in to the head space. A problem with horizontal cylinders. Needs new rings.

Steve.

Steve, February 2010

my rotovator stops when it starts to dig, but runs fine above ground.

simon, December 2008

Go to Briggs&Stratton web site,search for online manuals,download &print. Model 92500 series.It is available.
Seems like overfueling,choke sticking. Mine has same problem. There is adjuster screw at rear of engine..thro small hole in fueltank carrier bracket.
Turn screw clockwise until it stops-dont force it,then turn anti-c/w 1.5 turns. start engine,let it warm up.Now turn a-c/w until idle is fast but not 'cloggy'.
Anyway, I'm hoping someone will steal mine !.

Tim2, July 2008

There is no float on this model. the carb sits straight on top of the fuel tank .
if i manage to get it running , it runs for about 5 seconds smoothly then hunts and if i use it in the ground it cuts out. it sounds like there is an eratic spark bit points and condenser are fine.

Neil, June 2008

Black exhaust smoke is indicated when there is too much petrol (in the air fuel ratio) being drawn into the engine. Check for a Fuel float that is'nt floating by submersing in fuel to see if it sinks or fuel is heard inside it when shaken. Check the float is free to move in the float chamber onits pivot pin if it has one. Check the float needle valve is closing off the supply to the chamber when the float rises to its proper maximum height. Check jets have not become loose or fallen from there correct positions.

Bazzal, April 2008

Hi Tim.
There is plenty of compresion. I cannot turn engine by hand on bottom pully and i can feel there is plenty of comp on pull cord. I dont have access to a propper compresion tester.
and i cant keep my finger over sparkplug hole when puling cord.

Neil, April 2008

have you tries a compression test on it ? i have one the same throwning out smoke and the rings have worn out !

tim, April 2008