I've read a bunch of the messages here and I'm still having trouble.

My engine is a B&S 31C707-0603-B2, 17.5hp.

The engine died while mowing.

It ran a little afterwards but extremely slowly.

I took the valve cover off and found the bottom most valve had lost its spacer and seemed also to be very loose.

I reassembled and reset the valves.

The engine cranked once while I had the valve cover off.

Thought I was OK so I put the cover back on.

The engine will crank until it is fully compressed and won't go further.

Has new spark plug, oil, clean air filter.

Battery was run down from working on it but am trying to crank using a jump form the car that is running so there is power there.

Shorting power straight to starter doesn't start it.

Engine seems too "tight" at end of stroke to start.

Starter feels really strong but don't know how to assess that.

Any ideas? Could it be a weak starter?

Also, when the spacer popped out the push rod seemed to be out of place but putting it all back in place the valves open and close.

Thanks

Dave