I have a 3540p mcculloch mower, it starts without a problem but will not power down when the lever is released, if anything it runs smoother!!! I have cleaned all the linkages and the jets in the carb, all is operating fine but still doesn't shut down?

james, September 2016

on some of these there is a small cut out near to the brake
these will get covered in grass and muck clean and make sure it has a good contact.

cv, May 2017

The horsepower you suggest is clearly a typo - 3.5 hp from a 150 cc engine is more likely.

Two things should happen when you release the leaver to shut it down - a mechanical brake on the flywheel - and the operation of the kill switch to shut off the ignition (spark).

It seems from what you say that the cable that runs from the lever to the engine is not operating properly - you might do well to examine each end of it to see why it's stuck in the operate position.

Good Luck..., September 2016