Small Engines (Lawn Mowers, etc.): John Deere 425 engine problem - stall, twin cylinder engines, carburetor jets

Question
John,
I own a 425 20hp garden tractor.  It mows for 10 to 20 minutes and then starts to choke out.  After I let it sit for 15 - 30 minutes, I can restart it and mow again for another 10 to 20 minutes before choking out.  I have changed the plugs and the gas and it does not make a difference.

I noticed you had responded to a similar issue from a person named 'Doug' on 7/11/2006.  I believe my tractor is having a similar problem.  Do you have any additional information that could help solve this issue?

Thanks,
Ron

Answer
Hello Ron:

There are 3 Items that are Time Sensitive. 1- the Gas Tank Cap. If the Cap is Not Venting the Tank Properly, it Usually Takes 10 to 20 Minutes for a Vacuum to Build and Restrict the Gas Flow to the Carburetor even if there is a Fuel Pump. 2- The Coil/Magneto/Ign Module will Heat Up and Quit Firing the Plug after 10 to 20 Minutes. 3- Usually Withn 10 to 20 Minutes the Carburetor Shut Off Solenoid will Heat Up and Shut Off the Gas Flow to the Carburetor Jets. 4- The Valves Require Resetting (OHV Engines) 1- Make Sure the Gas Cap is Venting the Tank Properly. 2- Operate the Mower as Usual. When it Quits, Check for Fire at the Plug. **NOTE: BE CAREFULL THE ENGINE AND PLUG ARE HOT** 3- If the Plug is Firing, then Remove the Carburetor Solenoid and Go to the Hardware Store. Purchase a Bolt of the Same Diameter and Threads. It Needs to be 3/4" Long. Put this Bolt in Place of the Solenoid. If this Corrects the Engine Problem, then Replace the Solenoid. ***NOTE: THIS IS FOR CHECKING THE SOLENOID ONLY I NEVER SUGGEST YOU OPERATE THE ENGINE WITH THE SOLENOID OUT OF THE CARBURETOR EXCEPT FOR TESTING PURPOSES*** Sometimes the Plunger is Moving, Just Not Far Enough to Allow the Gas to Enter the Jets. 4- Check the Valve Clearance. The OEMs Suggest .004in on Both Valves. I Do Not Use the Setting Called for by the OEMs. I have Found that the Following Works Best. Remove the Valve Cover (on the Dead Cylinder for Twin Cylinder Engines). Set the Cylinder you are Setting the Valves on to Top Dead Center (Both Rocker Arms will have Play in them when the Engine is at TDC) When Setting the Valve Clearance. Now Loosen the Valve Adjuster Locks and Set the Intake Valve Clearance to .003in -.005in and the Exhaust to .008in - .010in. I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. 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