Briggs & Stratton Classic 35 running fast

[zuki79]

Morning all

i was given a petrol lawn mower which has a briggs an stratton classic 35 engine.

the engine runs (after a new plug) but seems to surge an runs basically a bit lumpy. there is no throttle on mine, so when you start it, it just runs then you release the brake which stops the flywheel which stalls the engine

im guessing the lumpyness could be the two small springs that operate the carb?

what do you think?

 

[Burnerman]

The long fine springs belong to the governor mechanism - best left alone really.
As I recall, these carbs have no adjustment on them fuelling wise, so run the engine without the air filter to see if it behaves better.
Its common for these motors to have an unsteady running sequence really - often the governor speeds the engine up, then slows it down a bit, but under load it compensates and usually runs more cleanly.
As you say, to stop the motor, releasing the run handle switches the engine off and brakes the flywheel at the same time.
John

 

[zuki79]

cheers john

i will try it

i was thinking maybe its the carb? possibly diaphram which im told is common on these to leak

it seems to stall pretty easy if grass gets stuck in the collector

 

[Burnerman]

Certainly, if its the engine where the fuel tank is below the carb, these are notorious for failure - but that is usually a starting issue.
If the engine has a priming bulb, the gasket between the air filter and the carb is another wrong 'un.
John

 

[ellal]

Had the same problem and it was the carb/filter diaphragm. Mine was also belching out a bit of black smoke.
You can get an unbranded one online for about £8.
Might be worth taking a photo of the spring arrangement when disassembling as they can ping out!