Small Engines (Lawn Mowers, etc.): John Deere L120, john deere l120, old john deere

Question
Original QA:   QUESTION: I have a 3 year old John Deere L120.  That has a
Briggs 20hp.  Since new it
will
intermittently back fire and loose power.  I have added fuel drier and cleaner.  
It is happening more and more.  Sometimes does not do it at all sometime
does it often.  I have change were I buy fuel and nothing helps.  When
running correctly or low on power I see no fuel in filter.  I have 25 years
experience at a high line auto dealer but no real experience with small
engines.  Any advice would be great.
Thanks Todd
ANSWER: My first thought is the seat switch doesn't have a good connection.

My second thought is why are you thinking so hard.  This tractor operates
just like any other engine. V-8, V-6, inline 4. They are all just engines.  This
just a V-2.  It works just like every other engine or car you have ever worked
on.
Question:

Answer
Hello Todd:

When you Say Backfire; is the Backfire through the Exhaust? If Yes, then Remove the Valve Covers and Check the Valve Clearances. The OEM Says .004in for Both Valves. I have Found that the .004in Works Well for the Intake and .008in - .010in Works Better for the Exhaust. I have Less Burnt Exhaust Valves and No Backfiring. You can View a Breakdown/IPL of the Mower at this Site Addy, http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.H... and Enter the Model Numbers and Click Find. Then Select the Sectional File. Then Select the Section of the Mower you Wish to View Online. Check the Gas Tank Cap and Ensure it is Venting Properly. You Say this is an Ongoing Problem that has Persisted Since it was New. That is the Complaint I have Had from Several Customers in the Shop and the Engines are From All the OEMs. Most Times the New Exhaust Valve Clearance Corrects the Problem. I have had a Few Where the Coil was Breaking Down and Causing this Problem, but it was Not on New Mowers, Just 4 or 5 Years Old or Older. Check the Flywheel Key. If the Flywheel Key is Damaged it will Throw Off the Plug Timing. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John