Briggs & Stratton Classic 35 (3.5bhp) runs rich...
 

Hi
I've seen older threads but don't seem to relate closely to my problem.
Mower is 5 years old. Recently (few months) began running slower than
normal and lumpy or slightly erratic. Speeds up to correct speed and
no lumpiness, just before fuel runs out.
This and the fact that the plug is sooty suggest rich running.
As I've replaced the plug and checked the gap, cleaned the foam filter
and recharged with oil there is only one thing left I guess & that's
the carb.
I notice that the two springs that possibly help adjust the fuel
mixture are very "soft" ie little tension. There is a good deal of
movement from them while the engine is running lumpy but I think that
is from the semi automated way the carb is set up.
I've read that the diaphragm on this carb can be affected by holes hair
line cracks etc and that there is a kit around that replaces this.
Can anyone confirm I'm on the right or wrong track here?
Any other ideas are welcome.

Briggs & Stratton Classic 35 (3.5bhp) runs rich...
 

"brush-head" wrote in message
oups.com...
Hi
I've seen older threads but don't seem to relate closely to my problem.
Mower is 5 years old. Recently (few months) began running slower than
normal and lumpy or slightly erratic. Speeds up to correct speed and
no lumpiness, just before fuel runs out.
This and the fact that the plug is sooty suggest rich running.
As I've replaced the plug and checked the gap, cleaned the foam filter
and recharged with oil there is only one thing left I guess & that's
the carb.
I notice that the two springs that possibly help adjust the fuel
mixture are very "soft" ie little tension. There is a good deal of
movement from them while the engine is running lumpy but I think that
is from the semi automated way the carb is set up.
I've read that the diaphragm on this carb can be affected by holes hair
line cracks etc and that there is a kit around that replaces this.
Can anyone confirm I'm on the right or wrong track here?
Any other ideas are welcome.


You say you checked the foam filter - what about the actual air filter. Mine
occasionally clogs up with fine grass/pollen and oil mist which you can
clean out/change filter if particularly bad.

Slurp

Briggs & Stratton Classic 35 (3.5bhp) runs rich...
 

brush-head wrote:
Hi
I've seen older threads but don't seem to relate closely to my problem.
Mower is 5 years old. Recently (few months) began running slower than
normal and lumpy or slightly erratic. Speeds up to correct speed and
no lumpiness, just before fuel runs out.
This and the fact that the plug is sooty suggest rich running.
As I've replaced the plug and checked the gap, cleaned the foam filter
and recharged with oil there is only one thing left I guess & that's
the carb.
I notice that the two springs that possibly help adjust the fuel
mixture are very "soft" ie little tension. There is a good deal of
movement from them while the engine is running lumpy but I think that
is from the semi automated way the carb is set up.
I've read that the diaphragm on this carb can be affected by holes hair
line cracks etc and that there is a kit around that replaces this.
Can anyone confirm I'm on the right or wrong track here?
Any other ideas are welcome.

Not quite the same problem as you've got - My mower was running rich,
lumpy performance and eventually stalling after a few minutes mowing. I
removed the carburettor and gave it a clean which seemed to fix it but
the problem re-occurred 15 minutes later....

I investigated carb service kits and found that a new one (including
pump spring, diaphragm and seals) was only £12 whereas the 'service' kit
was £14. I also bought replacement governor springs while I was at it.

New carb fitted (didn't bother with changing the springs in the end)and
the mower runs fine again...

Peter

Briggs & Stratton Classic 35 (3.5bhp) runs rich...
 

the Classic 35 engine only has one filter which is a foam one which is
charged with engine oil after cleaning (or you replace it).
Slurp wrote:
"brush-head" wrote in message
oups.com...
Hi
I've seen older threads but don't seem to relate closely to my problem.
Mower is 5 years old. Recently (few months) began running slower than
normal and lumpy or slightly erratic. Speeds up to correct speed and
no lumpiness, just before fuel runs out.
This and the fact that the plug is sooty suggest rich running.
As I've replaced the plug and checked the gap, cleaned the foam filter
and recharged with oil there is only one thing left I guess & that's
the carb.
I notice that the two springs that possibly help adjust the fuel
mixture are very "soft" ie little tension. There is a good deal of
movement from them while the engine is running lumpy but I think that
is from the semi automated way the carb is set up.
I've read that the diaphragm on this carb can be affected by holes hair
line cracks etc and that there is a kit around that replaces this.
Can anyone confirm I'm on the right or wrong track here?
Any other ideas are welcome.


You say you checked the foam filter - what about the actual air filter. Mine
occasionally clogs up with fine grass/pollen and oil mist which you can
clean out/change filter if particularly bad.

Slurp

Briggs & Stratton Classic 35 (3.5bhp) runs rich...
 

the Classic 35 engine only has one filter which is a foam one which is
charged with engine oil after cleaning (or you replace it).
Slurp wrote:
"brush-head" wrote in message
oups.com...
Hi
I've seen older threads but don't seem to relate closely to my problem.
Mower is 5 years old. Recently (few months) began running slower than
normal and lumpy or slightly erratic. Speeds up to correct speed and
no lumpiness, just before fuel runs out.
This and the fact that the plug is sooty suggest rich running.
As I've replaced the plug and checked the gap, cleaned the foam filter
and recharged with oil there is only one thing left I guess & that's
the carb.
I notice that the two springs that possibly help adjust the fuel
mixture are very "soft" ie little tension. There is a good deal of
movement from them while the engine is running lumpy but I think that
is from the semi automated way the carb is set up.
I've read that the diaphragm on this carb can be affected by holes hair
line cracks etc and that there is a kit around that replaces this.
Can anyone confirm I'm on the right or wrong track here?
Any other ideas are welcome.


You say you checked the foam filter - what about the actual air filter. Mine
occasionally clogs up with fine grass/pollen and oil mist which you can
clean out/change filter if particularly bad.

Slurp