Small Engines (Lawn Mowers, etc.): Rototillers / Sears Roto Spader, worn piston rings, libertymutual com

Question
Hi Mike -
I'm also a volunteer on All Experts, in the category of insurance, hope you can help.  I'm a pretty handy gal and take direction well.
Got this for $40- old Sears Roto Spader, not of the same model that chews your legs off, but reverse gear was removed.  It's got a 4hp 4 cycle Briggs & Stratton in it.  Runs good not under power after I fixed the crack in the gas line connection, but when you put it in the dirt it's like it's not getting enough gas and quickly boggs down and dies.  One suggestion I've had it to use a bit of STP Gas treatment in it to degunk the carb.  Do you have any other suggestions, diagrams of how a briggs engine like this work, or anything that will help a gal with a rototiller out in the stix get it running proper? Appreciate your time.  If you're responding during daytime hours, my work email is denise.krueger@libertymutual.com.  Thanks for your help! Denise

Answer
Hi Denise,

If it runs well and reaches full speed when you add throttle but lacks power under a load then I would suspect a lack of compression.  Worn piston rings, cylinder or valves.  You can check the compression with a gage.  There may be a lack of fuel flow to the engine but that condition usually results in low speed and stalling. You could try adjusting the carb for more fuel or have someone squirt fuel into the carb when it bogs down to see if that helps and points carb problems.  
The carb may need disassembling, cleaning or rebuilding and the engine may need rebuilding also.

If you can get the model and type numbers from the cooling shroud you may be able to look at parts or other manuals at: http://www.briggsandstratton.com/display/router.asp?docid=78484

Let me know how you make out.
Michael