B&S Engine Starts Cold, Won't Idle

[oldAggie]

I have a B&S 15 hp Intek engine (model 31R777) in a Snapper riding mower. When cold, the engine starts, and runs well enough to mow the yard, although there are occasional misses. However, the engine will not idle. When the engine is running and I move the throttle from full speed to idle, the engine stops after a few seconds. Also, if the engine has been running and is stopped, the engine will not restart until it has cooled down. I checked the valve clearances. Exhaust was OK, but intake appeared to be essentially zero clearance, so I adjusted the clearances on both valves. That did not resolve the problem.

Any comments will be appreciated.

 

[Scrubcadet10]

Could be a clogged idle circuit in the carburetor.. however that generally leads to surging as well... but i would apply choke when you idle it down and see if it will run.
I had a Kawasaki horizontal engine with a similar problem once, turned out the carburetor needed about 1/2 turn out on the pilot (idle) mixture screw, it does appear the carburetor for the Model does have one. some do, some dont.
Do you have the type number as well? 31r777-____-__

 

[Rivets]

Two things I would check. First, blown head gasket. With engine running loosen the dipstick carefully and set it on top of the tube. If it bounces around I’d be replacing the head gasket. Not that I would take a can of spray carb cleaner and spray around the intake manifold and gasket areas at half throttle. If engine speed changes, I’d be looking at a bad gasket or cracked manifold.

 

[oldAggie]

Thank you for the responses. I thought I had a blown head gasket, so I removed the cylinder head to check. The gasket looked perfectly good, so I concluded that wasn't the problem. I replaced the gasket and adjusted the valve clearances at the same time. I will get some carburetor cleaner and check for cracks.

The complete model number for the engine is 31R777-0052-G1. A simple carburetor adjustment would be great.

Thank you both again.