Small Engines (Lawn Mowers, etc.): honda 3813 runs rough, internal passages, jet needle

Question
John, I've got a Honda 3813 tractor.  It started running rough last season. It ran better under load and WOT, below WOT it would start to miss and foul plugs (carbon). Now it fouls them more regularly, runs worse after 15-20 minutes.  It also idles smoothly but just off idle things go bad.  At full throttle, no load it surges against the governor and won't smooth out.  It has a kehin carb.  I have taken it apart, cleaned it, replaced the float needle, replaced the fuel filter, air filter and plugs.  Could it be an ignition problem?  Engine# 1198627, Frame# HT38135123341.  Thanks!

Answer
Hello Jim:

Usually What you Described is a Carburetor Issue. Did you Soak the Carburetor Overnight in carburetor Cleaner (I use Gunk) and then Blow Out the Passages with Compressed Air? If you Just Used Spray Carburetor Cleaner, then the Carburetor can Still be the Cause of your Problem. **1/4 to 3/4 Throttle: Changing the STRAIGHT DIAMETER (D) will Change the Calibration in the Transition Range from the SLOW Circuit to the MAIN Circuit (1/8 to 1/4) Throttle. A Smaller Diameter will make this Range Richer and a Larger Diameter will Lean this Range. TAPER (A) Changes are Only Made if there is a Problem Balancing the Calibration between 1/4 and 3/4 Throttle. If the Mixture is Rich at 1/4 Throttle and Lean at 3/4 throttle, a JET NEEDLE with a Larger Taper is needed. If Mixture is Lean at 1/4 Throttle and Rich at 3/4 Throttle, Change to Smaller Taper. If the Calibration is Lean from 1/4 to 3/4 Throttle, Raise the JET NEEDLE by Lowering Clip Position, or use a JET NEEDLE with Shorter Length (L1). If the Calibration is Rich, Lower the JET NEEDLE with a Longer (L1). Wide Open Throttle: Changing the MAIN JET affects this Range. Select the Size of MAIN JET which offers the best W.O.T. Performance, then Install One Size Larger MAIN JET for Ideal Engine Durability**. The Above is True Also if the Jets and Internal Passages are Restricted by the Varnish that Gas Forms Inside the Carburetor Over Time. The Air Screw is Most Effective between Idle through 1/8 Throttle. The Pilot (slow) Jet is Most Effective between 1/8 through 1/4 Throttle. The Slide Valve is Most Effective between 1/8 through 1/2 Throttle. The Jet Needle is Most Effective between 1/4 through 3/4 Throttle. The Main Jet is Most Effective between 3/4 through Wide-Open Throttle. It May Also be an Ignition Problem. Until the Carburetor is Properly Soaked and Cleaned and Tuned, you Really can Not Look for an Ignition Problem. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 9pm EST (US). My New Day Starts then. Thanks.

Respectfully

John