Small Engines (Lawn Mowers, etc.): Lawnmower engine stalls when vehicle set in motion, head gasket, ride on lawnmower

Question
Hi there,
We have an ancient Westwood ride-on lawnmower (probably about 15 years old); 400cc, 11hp, electronic ignition.(sorry I don't have any model details - they've rusted off!). It has worked pretty much flawlessly in the time that we've had it, however just this year it has been giving us grief. Basically, it will only run with the choke fully engaged, but even then doesn't sound quite right (misfiring a little). When you engage gear and start moving, the engine dies completely. Needless to say, it is not even worth bothering with the cutting blades, but the same thing happens when they are engaged as well! I note you recommend thoroughly cleaning the carb, which we have done (although not with tag wire - what is this?). Also, we've cleaned the spark plug and washed out the fuel tank and refilled with fresh fuel. Any ideas? Looking forward to hearing from you.
Regards,
Julian

Answer
Julian, based on the engine's age, you may have to remove the cylinder head and check the valves for seating as well as the head gasket. Also, check for a loose carb. It sounds as if some major work is needed especially if the bore is worn,that is if there is a ridge at the top of the bore you can feel with your fingernail.  Lety me know what yu find....bob