Small Engines (Lawn Mowers, etc.): Kawasaki FH721V wont start when hot, 4 stroke engines, electronic coils

Question
Friends have purchased a second hand Husqvarna zer turn fitted with a 25HP Kawasaki FH721V.It starts "ok" when cold runs fine, but when hot cranks and most often will not start unless left to sit a little. It kind of "burbles" out the exhaust whilst cranking. Must be at low idle to start when hot. Cleaned cab, reset valves to 4 thou.9 (were 9-10) Cleaned and re-gapped coils. Been a little better since then, as in will start sometimes nowwhen hot. Takes a little cranking even when cold, but always starts. Has externally vented carb,but has a Donaldson type aircleaner which looks original. Was suckng air through tank changeover valve but fixed that. Checked key, no problem there. Spark looks ok, not a big fat blue but local guys tell me that is normal for these electronic coils. Where next???

Answer
Hello Glenn:

You can View a Breakdown of the Engine at this Site Addy; http://www.buykawpower.com/kmcb2c/main.jsp and Select Parts Catalog on the Lower Left of the Page. Now Select 4 Stroke Engines. Now Select your Engine Model. Will the Engine Start and Quit if you Spray Starter Fluid (or Gas (Just be Carefull)) when Doing this Check)  Into the Carburetor Throat This Engine has a Carburetor that Uses a Carburetor Solenoid that is Designed to Prevent Backfire when the Engine is Shut Off. It Closes Off the Gas Flow to the Main Jet.  Check the Carburetor Solenoid. It May be Getting Hot and Not Operating Correctly. You should Not have to Worry about the Voltage to the Carburetor Solenoid, so you can Skip the Voltage Check in the Instruction File Unless you Think that May be a Possible Cause for this Problem. Following is a Basic Instruction File I made for Checking the Carburetor Solenoid. Any Input is Appreciated. **Check for Current/Voltage (10.5 VDC Minimum) to the Carburetor Shut Off Solenoid. If the Carburetor Shut Off Solenoid has Current, then On Some Solenoids you can Remove the Needle and Replace the Solenoid to Test them. ****PLEASE DO NOT OPERATE THE MOWER WITH THE SOLENOID BYPASSED IN THIS MANNER. THIS IS "ONLY" FOR TESTING.**** For Others, Remove the Carburetor Solenoid and Go to the Hardware Store. Purchase a Bolt of the Same Diameter and Threads. It Needs to be 1/2" to 3/4" Long for the Horizontal Mount Solenoids and 1/4" Long for the Vertical Mount Solenoids. 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 Jet Properly.**  Have you Checked the Gas Tank Cap and Made SUre it is Venting the Tank? If the Cap is Not Venting Properly, then the Problem you Described will Occur. Have you Checked the Fire when the Engine was Hot and would Not Start? Was/is there Spark? If you have Spark when the Engine is Hot, then What is the Compression when the Engine is Hot and will Not Start? If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. I Hope you Had a Happy Holiday Season and May the All Mighty Bless You and Yours. Be Safe and Happy. 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 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John