QuestionQUESTION: Iam working on a toro zmaster 355.Its a kohler engine family #3khxs.7252 gc,dip. (cc) 725,model#ch730s,spec#ch730-0073,serial#3313216991.Its a command pro 25.Thank you for all the help that you provide to everyone.
The engine runs smooth at idle,but when its throttled up it starts to blow black smoke and backfires.I pulled both plugs and they were black.I pulled the carburetor,rebuilt it then reinstalled it.It seemed to run better, but still smoked,and back fired at full throttle.It seems like it's not reving up enough so I used your advice on setting the govenor.AT ONE POINT WHILE IT WAS RUNNING IT SMOOTH OUT AND RAN REALLY GOOD THEN AFTER ABOUT 2 MINUTES IT STARTED DOING IT AGAIN.Tomorrow Iam going to drain the gas tank just in case it has water in it.The way it acted today when it ran good it almost seems like it has water in the gas,or it's jumping time.Its not my mower it belongs to a friend who owns a lawn service.I normally work as a diesel mechanic,but ive been laid off for the month of jan.If you can help me I would greatly appreciate it.Maybe he'll send more work my way .I soaked the carb.all night,and cleaned every hole and corner in it.Thank you again for making a deference to everyone Johnny
ANSWER: Hello Johnny:
>>I am Glad to Assist. Thanks.
>>I Started Working on Lawn Equipment when I was about 12 and went Into Gas Engine Repair and Finally Diesel Engine Repair even though I Still Repaired Lawn Equipment at Night.
>>The Gas and Diesel Engine Repairs Turned into the Nights and Weekend Repairs and the Lawn Equipment (Small Engines) became the Career Job. LOL.
>>You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM (Kohler) and Enter the Model and Spec Numbers (CH730-0073). Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View.
>>Has the ACC Pump been Rebuilt? If the ACC Pump Diaphragm is Bad you will have this Problem.
>>A Bad Diaphragm in the Vacuum Fuel Pump will Cause this Problem. Depending on How the Vacuum Line for the Pump is Routed, the Vacuum Line for the Pump will Draw Gas Into the Intake if the Diaphragm has a Pin Hole in it and the Gas Flow to the Carburetor will Seem to be Correct.
>>On the OHV Engines, a Blown Head Gasket between the Cylinder and the Push Tube Galley will Cause this Problem. It May or May Not Smoke at Idle but when Throttling Up the RPMs, then Engine will begin to Smoke as you Described. (I Do Not Think this is the Cause of your Problem, but It Might be)
>>Does this Carburetor have Air Mixture Screws?
>>The Following is the Instruction File for Setting the Air Mixture Screws. Any Input is Appreciated. The Procedure is the Same for 1 or 2 Mixture Screws, Just Use the Instruction File and Skip Over the Section with the Missing Mixture Screw ( Usually the H Mixture Screw).
>>Now Setting the Air Mixture Screws:
>>****Turn the Idle Air (L) and Main Air (H) Mixture Screws In Until SNUG **Do Not Jam** Then Reverse Both Screws 1 1/2 Turns. Set the Throttle Full Open, Start the Engine.
>>Turn the Main Air (H) Mixture Screw Clockwise Until Proper Revs are Obtained. **Carefully Use your Finger and Move the Governor Arm to Rev the Engine (on Chainsaws and Trimmers Use the Trigger to Rev the Engine) Until you Reach Max RPMs (on Chainsaws and Trimmers, the RPMs are Not Set to MAX. Set to Max and then Reverse the Setting Screw 1/4 or 1/2 Turn. If the H Mixture Screw is Set too High; the Engine will be Starved for the Oil in the Gas and Damage the Piston and Jug/Cylinder) and the Engine is Running Proper at Full Throttle Up a Grade. Occasionally you May have to Turn this Counter Clockwise to Achieve the Proper Revs.**
>>Now Allow the Engine to Idle. Set the Engine Idle Screw (Not Idle Air) so the Engine will Stay Running if Required.
>>Now Set the Idle Air (L) Mixture Screw so there is No Hesitation when Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.****
>>Please, Do Not Hesitate, If you Hit a Snag, if I Missed Something or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. 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
---------- FOLLOW-UP ----------
QUESTION: Hello again john and may god bless you.This is a follow up on the toro z master command pro 25 engine family #3khxs.7252gc,disp(cc) 725,model#ch730s,spec#ch730-0073,Serial#3313216991.I looked on the web site you recommended thats a lot of help thankyou.I pull the carb. back off to rebuild the acc pump.I don't know the results yet(parts are ordered).Just for grins i put my hand over the intake to see if it had blow by from the head,and it had sucktion.My question is what can I do to check for a blown head gasket?Just to give you a brief reminder the engine runs great at idle,But when its throttled up it begins to skip,backfire,and blow black smoke out the exhaust.when I removed the carburetor there was excessive gas in the intake.The diaphragm was flexible and had no obvious signs of tears or cracks.Iam going to rebuild it anyway as you recommended.Any information that you can give me or web sites you can steer me towards will be appreciated.Thank you Johnny Walker.May god reward you greatly for the help that you provide to his children.
ANSWER: Hello Again Johnny:
>>Thanks for the Comments and Ratings. It is Always Great to Hear from the Questioners.
>>These 2 Site Addys are Good Viewing for Carburetor Rebuilding.
>>1- http://www.repairfaq.org/samnew/lmfaq/lmclctc.htm
>>2- http://www.cpdonline.com/692509.pdf .
>>Other than Removing and Inspecting/Replacing the Head Gasket; there is Not Another Way to Check for a Blown Head Gasket. A Blown Head Gasket between the Push Tube Galley and the Cylinder will Not Always cause Problems Idling, Just when Revving the RPMs Up.
>>Are you Sure the Carburetor Float is Set Correctly?
>> If the Float is Set too High you will have this Problem Also.
>>An Intake Valve that Requires Seating/Lapping will Cause this Problem.
>>Is it Possible the Flywheel Key has been Damaged? If the Flywheel Key has been Damaged, then you will have the Problem you Described.
>>Please, Do Not Hesitate, If you Hit a Snag, if I Missed Something or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. 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
---------- FOLLOW-UP ----------
QUESTION: I rebuilt the acc,and carb.It ran great.I cut my grass with it approx.45 min.The guy picked it up the next day and brought it back.Now its not smoking at all,but is low on power,and spitting gas up and out of the carb.Iam suspecting a valve on the intake side.I took the carburetor off.Then i took the intake rocker arm off the left side and the intake had sucktion.Then i put it back on and removed the right side rocker arm on the intake side,and it didn't seam to do anything.While the carb was on i looked down the throat of the carb and could see it firing under the swash plate.My brother suggested checking the compression on both sides,and checking to see if the rod that the rocker arm bolts to has wear allowing the rocker to tighten down to far leaving the valve slightly open.I haven't done either one yet do you have any suggestions.All the valves are moving correctly,and the push rods look straight.Sorry it took so long to answer i thought i had it fixed.May god bless you Johnny
AnswerHi Johnny:
>>No Worries. This Happens to the Mechanics in the Shop All the Time and it has Happened to me More Often that I like to Admit. LOL.
>>The Shop will Send a Unit Out Repaired and After a Few Weeks it is Back with Another Problem that was Not Evident when it was Tested in the Shop and Certified to be Repaired.
>>You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM (Kohler) and Enter the Model and Spec Numbers (CH730-0073). Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View.
>>From your Description I Suggest you Check the Intake Valve. It Sounds like the Valve May have a Burnt Valve Seat on the Valve or the Valve Seat in the Block and this is Allowing Blow Back Into the Carburetor which Causes Power Loss.
>>You May have to Reseat (Lap in) the Valves.
>>This Engine Uses Hydraulic Lifters and there is No Valve Clearances to Set.
>>This Web Page; http://www.affordablegokarts.com/va
lve-lapping.php has a Fairly Good Description and Instructions on Valve Lapping and a Good Explanation of what to Look for when Seating the Valves.
>>Please, Do Not Hesitate, If you Hit a Snag, if I Missed Something or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. 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
Hi Johnny:
>>I Just Read your Comments/Ratings and had a Few Minutes to Say Thank you; Instead of Sending out the Usual Computer Generated Thank you Note.
>>Ideas (Possible Causes) is All I can Give. LOL. If Anyone Requires More Detailed Instructions on How to Actually Perform a Certain Repair/Diagnostic; I can Usually Direct them to a Site that Explains How to do the Repair/Diagnostic Better than I can Put Into Words or I Try to Explain in Detail How the Repair/Diagnostics is Performed.
>>I Generally Try to List the Possible Causes in the Order that they Occur the Most for the Problem the Questioner is having and Sometimes I May Miss a Step. I am Only Human and I Do Make Mistakes like Everyone else.
>>Thanks Again for Using All Experts. Till Next Time. May All Your Mechanical Problems be SMALL ONES and May the All Mighty Bless You and Yours. Be Safe and Happy.
Best Wishes and Good Luck
Respectfully
John
