In a nut shell, the Carb. on my 12hp B&S riding mower (32"-1991 Ariens rear engine) decided to throw one of its two throttle plate screws, which was sucked into the engine with a terrible sound.

I removed the Carb and found that the throttle shaft had snapped where the throttle plate seats, which explained the lack of throttle control I was experiencing on that particular day.

Luckily, I shut the engine off as soon as the noise of the screw being smashed by the piston occurred. I slowly turned over the engine manually (without trying to start it) by the pull cord to listen to what was going on and found that there was still compression and exhaust noise on each cycle. It turns out that the remains of the screw must have worked its way down to the exhaust valve during the manual pull throughs. That's where I found it after removing the muffler from the head as part of the carb removal. The engine runs fine with no oil burning or strange noises.

Anyway, called the lawn mower shop and they wanted $350 for diagnosis/repair/transport of the mower. Decided to DIY and ultimately, all it needed was a rebuilding of the carb which I performed with the help of the link below. I just googled the B&S engine #281707.

http://outdoorpowerinfo.com/repairs/...o-jet_carb.asp

Final cost was $60 for a Carb overhaul kit, throttle shaft, plate screw and breather assembly.

Just thought I'd share.

 

Nice, lawnmower shops are a ripoff.