DIYbanter - View Single Post - Briggs & Stratton 3.5hp running too rich? (Cutting out)

wrote:

Hello everyone! I have a Briggs and Stratton 3.5hp engine fitted to a
Hayter rotary mower from the mid 1970s. The Model number is 92982 and
the Type number is 1640-01. It's a 4 cycle, single cylinder, L-head,
air-cooled engine for information.
The problem is I have had it sitting idle for 5 years as the starter
rewind spring broke and lack of time prevented getting it sorted
sooner. Last week I bought a new spring, rope, (approved Champion/B&S)
spark plug and air filter foam element (old one was disintegrating,
saturated new one with oil and squeezed excess out), filled the sump
with fresh oil and put in half a tank of fresh 95RON unleaded.
So far, so good. But pulling the rope and some carburetor needle valve
tweeking got the engine to start eventually, burning off the oil I had
put in throught the spark plug hole. It then splutters and pops (rich
mixture burning within the exhaust?) The spark plug has looks like it's
not running lean (fuel/oil on it). It then cuts out (maximum of about
15 seconds after starting). Then you can restart straight away. Any
ideas as to the adjustments I need to do (I have found I can start it
and get it to idle very slowly with the throttle lever set to minimum).
Do I need to play with the idle adjustment screw? Is there the
possibility that the carburetor needs new parts too? I've heard B&S do
carburetor kits - how much would I be looking at (UK Pounds) and what
parts do they contain - anyone ever used one?
I know this is a long posting, but i'm not too hot on my knowledge of
getting carbs to work perfectly for a smooth idle.
Thanks in advance. (This email address is invalid because of spammers
so reply on here).

Ive got that model, from the mid 80's tho.

I had a huge problem with mine, traced eventually to te fact that when
it had been serviced and teh head overhauled, they had failed to set the
thibng up so that it had any choke on 'maxiumum rabbit' whatsoever.

It may be that yours has a similar problem in reverse - the choke is
permanently on. That, or a bolcjeked air filter, are all I can think of
to suggest rich running - which will be lumpy, smoky and prone to
stalling when hot.

Pull the air filter right off and try again, and see whether the choke
is in fact working correctrly. From memory it should be spring loaded to
flap inline with the airflow when not required. It may simply have
gummed up.