Small Engines (Lawn Mowers, etc.): Kohler Engine Running Rough, hp engine, loose piece

Question
I have a 60" eXmark TTHP with a Kohler 23 hp engine on it. The engine specs are: Kohler 23hp CV23S Spec: 75559 S.N.: 3225503391. The symptoms are every time hot or cold, when I go to full throttle it runs rough like it is missing. I have noticed a little black smoke on occasion while it is doing this. The plugs look good although there is a little black on the left one – not much though. I can just as consistently clear it up by throttling down and then quickly back up. After this it runs smooth until I slow it down or restart it. It also, most of the time, back fires when I shut it off. It will do this even when I let it sit at idle for ten or more seconds although it is worse when I throttle down quickly and shut it off. Both cylinders read 150 PSI when compression tested. The left did seem to go to 150 a little slower than the right did. I have had the carb all the way apart and cleaned it thoroughly not to long ago. Also, I replaced the carb diaphragm for a different problem last year. It sounds (all the time like one of the muffler gaskets is blown out. This just started this week. The other problem has been going on for several months now. I did have a problem with the muffler several years ago. I opened it up and either tacked back in a loose piece or removed it. I am not sure which. That problem cleared up when I did that.

Any thoughts will be appreciated.

Answer
Hello Ed:

>>1- Check the Carburetor Solenoid.
>>The Backfiring Tells me that the Solenoid is Not Operating as Designed.
>>The Solenoid is Supposed to Prevent the Engine Backfiring.
>>The 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" to 1/2" 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.**  **Use 440 Wet Dry Sand Paper and Engine Oil to Clean the Pin. Wet the Sand Paper with Oil Until it is Flexible and then Lightly Polish the Pin. There is Some Slop/Free Play in the Solenoid Pin. Usually the Electromagnet is Simply Not Pulling the Pin as it Should or there is a Small Bur on the Pin. Use 440 Wet Dry Sand Paper and Engine Oil to Clean the Pin. Wet the Sand Paper with Oil Until it is Flexible and then Lightly Polish the Pin. Clean and Lightly Oil the Pin before Inserting it Back into the Solenoid. Just a Film of Oil is All it Takes.**
>>If the Solenoid is Good, then
>>2- I Suggest you Remove the Cylinder Head on the Left Cylinder and Inspect the Valve Seats.
>>I have had a Few of these that have had Loose Valve Seats (Exhaust Valve Seat usually) and you Described the Problem to Perfection.
>>This may Not be the Cause, but from what I have Seen it is Better to Inspect the Valve Seats Now before the Block is Damaged and a Short Block or New Engine is Required.
>>I Suggest you Allow the Engine to Run for Approximately 2 Minutes to Prevent Backfire.
>>It takes this Long for Any Gas Vapors in the Exhaust to Clear Out so the Engine is Less Likely to Backfire.
>>You can View a Breakdown of the Engine at this Site Addy; http://www.kohlerplus.com/login.asp (IE5 or Higher Required) and Select Enter as Guest. Now Select the Thumbnail of the Engine Catalog you Wish to View.
>>If you Hit a Snag or this Does Not Correct the Problem,  I Hope to be Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 5 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