Mower won't crank over with spark plug in?

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skin1235, May 7, 6:21pm
being as we actually have no idea what model he has the point is quite moot
there is still a hell of a lot B&S 13hp single banger side valve engines with no decompression systems out there, I have a couple here too, neither of these have adjustable valves you can adjust without pulling the head and the valves and regrinding the seat or the valve
if he has an overhead valve machine most of your comment s are valid, none of them are if he has a sidevalve non adjustable as many are

timbo69, May 7, 6:56pm
If it isnt OHV I would still check and adjust valve clearances which you can do, I did it to an older 12.5hp a month ago - its not that bigger job and can see condition of bore/valves/valve seats all for the cost of a head gasket ( or possibly not)

bikernutrr, May 8, 4:02am
Thanks for the advice everyone. Had time this afternoon to take the cylinder head off the B&S 13HP model: 28m707 single cyclinder motor. Its not a OHV motor. Air filter was dirty but ok, took exhaust off but seems fine, turned motor by hand and valves appear to be working in order correctly. I'm guessing either the starter motor is 'weak' although still turns over without plug fine until I insert plug then slow again, or need to adjust valves but will have youtube it as never done before.

motorboy2011, Feb 7, 3:58am
Pull the starter motor off and check the brushes. From memory new brushes cost me $50ish