17.5 hp blowback

[jemel]

17.5 hp intek won’t start and blows back through the carburetor.

 

[ILENGINE]

Start by removing the valve cover and make sure both push rods are in place and not bend or broke. Also make sure both valves are the same height ( ie checking to make sure both valves are closing properly and not have a valve seat that has fallen out of the head and holding the valve open. And if that checks out then set the valve clearance to the proper spec and see what happens.

 

[StarTech]

Also make sure both rocker moving by the same amount as the exhaust lobes are known to wear round on the 793880 camshafts. Plus the aluminum intake push rods do wear in two at times but you said you had blow back so suspect the camshaft is the culprit if not a blown head gasket which these are also a known with the 310000 series engines.

 

[shadetree#1]

Check compression or leak down.
I've seen the valve seats come loose and hold valve open on those engines, usually due to the cooling fins being clogged clogged with oil soaked grass clipping restricting the air flow around the head and overheating.