This is going to require removing the valve covers to determine the cause.
Some possibilities include a blown head gasket or defects involving the valves.
I would look for a blown head gasket first.
To check for blown head gasket you will ideally need a shaded spot to work and a good bright light to illuminate into the pushrod galley (where the pushrods come out of the engine).
Beware that there will be some slinging and spattering of lube oil during this check, so suitable attire is a must.
You can check one head at a time, or you can have both valve covers off at the same time.
Having both off might be a bit messier (oil wise) but it will give better viewing of the suspect location.

With the engine running at idle RPM, shine your light into the pushrod galley.
Look at the place where the cylinder head meets the cylinder block. A blown head gasket will issue a very obvious jet of pressure escaping into the pushrod galley.
Compare one head to the other and if there is a leak you will recognize it.
Do this check and post back your results.
Not much point in going into the other possibilities until head gaskets have been checked out.

Thank you for the quick response. I will try this test when I get home this afternoon and post the results.

GL

Removed the left side valve cover and the intake pushrod was laying in the pushrod galley, bent. Both rocker arms appear to be loose, more than .030" valve lash.

In addition to replacing both pushrods and setting the valve lash is there anything else that should be done?

Thanks in advance,
GL

You should check to determine if the valve guides are firmly in place in the head and not "working loose".
The valve guide can be seen by looking through the coils of the valve spring.
If the guides are backing out, the spring retainer cup hits the valve guide when the valve rocker opens the valve (pushes valve down) and this can cause bending pushrods.
The most likely cause of the bent intake pushrod is due to the intake valve stem sticking to the guide while the engine is stopped. Then, when the engine is started up again, the valve stays stuck for a moment while the rest of the valve train moves away allowing the pushrod to fall out of the rocker. If the pushrod gets trapped on the edge of the rocker arm when this occurs, the next downward push of the rocker arm will bend the pushrod.
To help prevent sticking valves and guide you should change the lube oil often (50 hour intervals or sooner).
But, you really must start adding some "upper cylinder lubricant" to your fuel supply to properly lubricate the portion of the intake valve stem that is exposed to the incoming fuel/air mix from the carb.
Gasoline and ethanol are both highly solvent and tend to wash off the engines natural coat of lube oil on the intake valve, then the solvents evaporate..........leaving a very gummy residue.
If the intake valve happens to stop in the open position when you shut the engine off, all bad stuff happens.
Upper cylinder lube can be had in the form of Marvel Mystery Oil or any good 2-cycle fuel mix oil.
If you use 2-cycle mix oil just add a volume of oil amounting to about 4 or 5 standard soda bottle caps of oil to a single gallon of gas.
An ounce of prevention is worth a pound of pushrods!
Do you have the service manual? If not, e-mail me for a PDF copy.

IF your valve guide HAS worked up, it will not stay in place by simply pushing it back where it belongs. B&S says the only fix is a new head. I have a permanent fix, address below, put in proper format and remind me.

Another cause of the valve guide coming loose is excessive heat in that area due to plugged cooling shroud or fins OR one mfg. ran the exhaust too close to the head causing excess heat.

Walt Conner
wconner5 at frontier dot com