QuestionQUESTION: John
I have a 21hp Craftsman that has me stumped. Last year, it blew a head gasket and while they were repairing it, I went ahead and put 2 new heads on as I was told the valves looked bad as well. At any rate, I used it all last season and it ran well, other than after it was at operating temp it would sometimes backfire thru the carb when turned off. At the last mowing of the season, it would not pull on an incline, with or without blades running. Seems to do well on level surface. I ran seafoam thru the system to give it a cleaning but no improvement. It also seems to drag a little when starting after the engine is hot.
The motor is a Briggs and Stratton 21hp intek. The model number under the seat is 917-273280.
Any suggestions are appreciated.
ANSWER: Hello Scotty:
>>From your Description it Sounds like the Valve Clearances Require Setting or the Fuel Line Clamps Require Replacing.
>>The Following is a Basic File I made for Setting the Valve Clearances. Any Input is Appreciated.
>>**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).
>>Check the Push Tubes and make Sure they are Not Bent.
>>Set the Cylinder you are Setting the Valves on to Top Dead Center on the Compression Stroke When Setting the Valve Clearance. Now Loosen the Valve Adjuster Lock and Using a Blade Style Feeler Gauge, Set the Intake Valve Clearance to .004in -.006in and the Exhaust to .006in - .008in. Loosen and Tighten the Rocker Arm and the Feeler Gauge is Placed Between the Rocker Arm and the Valve Top where the Rocker Arm Pushes on the Valve.
>>***BE SURE TO TIGHTEN THE ADJUSTER LOCK AFTER YOU HAVE THE PROPER VALVE CLEARANCE***
>>I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. Be Sure the Piston is at TDC on the Compression Stroke.**
>>If you Remove the Valve Cover and then Turn the Engine by Hand, you can Watch the Intake Valve Movement. When the Intake Valve Closes, the Piston will Just Starting the Compression/Power Stroke.
>>On Some Engines you can Us a Straightened Coat Hanger and Feel the Piston.
>>Be Careful and Don't Jam the Wire in the Cylinder. Usually the Piston will Push the Wire Out of the Spark Plug Hole with No Problems.
>>2- If the Engine Fuel System the Spring Style Hose Clamps, then Replace them with the Screw Style Clamps. The Spring Clamps Lose Tension over Time and Allow Air to Enter the Gas Line.
>>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. 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
---------- FOLLOW-UP ----------
QUESTION: John
I have reset the clearances on the valves and found them to be off slightly. I now have another issue. I started the mower and it cranked easily, then after running less than 1 minute, it began to billow large amounts of white smoke from the exhaust. Allowing it to run briefly did not alter this. I shut it down and checked the oil which seemed to me to be possibly overfull slightly. I could smell a rather strong smell of gas in the oil. I have now drained this and am allowing the oil system to remain open, including filter, for several hours. I did not find a lot of oil in the air filter, but I am changing it anyway. I do not have the ability to do a compression check, although when the new heads were installed I was told the cylinders look fine. Suggestions at this point? Im hoping it is not another head gasket, I do not have a service manual and I have never removed the heads. I did check the plugs and both appeared about the same condition, slight tan in color with no oil deposits.
Thanks in advance,
Scotty
AnswerHello Again Scotty:
>>As you may have now Realized, the Valve Clearance on the OHV Engines are Critical and must be as Close to the Correct Settings as Possible in Order to Start and Run Correctly.
>>You may have a Problem with the Clearances Requiring Setting again in the Future. It is a Common Problem with OHV Engines.
>>The Problem with the White Smoke is Gas in the Crankcase Due to the Carburetor Float Needle Valves Not Closing properly and is Allowing gas to Flood the Engine Crankcase.
>>The Following is an Instruction File I Made for the Gas Contamination of the Crankcase Oil and/or Blowing White Smoke when Running. Any Input Concerning the File is Appreciated.
>>Depending on the Engine Model, Usually the Gas in the Crankcase Oil or White/Blue Smoke is Caused by the Carburetor Float Needle Valve Not Seating Properly and Allowing the Gas to Flood the Carburetor and Engine. Then the Gas Seeps by the Rings and Enters the Crankcase and Contaminates the Crankcase Oil.
>The Smoking is Caused Not Only by the Flooded Crankcase but can be Caused by 1 of the Following; a Bad Diaphragm in the Fuel Pump, a Blown Head Gasket between the Cylinder and Push Tube Galley, the Crankcase Vent Stuck/Frozen/Broken or the Carburetor Flooding the Engine.
>>1- Clean the Carburetor and Replace the Float Needle Valve (and Seat if this Model has One). A- **Remove, Disassemble and Soak the Carburetor Overnight in Carburetor Cleaner (I Use Gunk). I have Found that Most People can Use a Breakdown/IPL and Disassemble the Carburetor Enough for Proper Cleaning. You Only have to Remove the Bowl (if Applicable), Float Pin (if Applicable), Float (if Applicable) and Needle Valve and Any Adjustment Screws that Go Into the Carburetor Body. The Welch Plugs Do Not have to be Removed. Then Soak the Carburetor Body and Parts in a 1 Gallon Can of Gunk Carburetor Cleaner Overnight. The Can has a Parts Tray Inside it for the Small Parts. Once the Carburetor and Parts are in the Cleaner, you can Replace the Lid for Safety and to Prevent Accidental Spillage. Then Blow Out the Passages with Compressed Air. Install New Parts if Required.**
>>If the Carburetor Float Needle is Good, then; 2- Block the Outlet Port and Pull a Vacuum on the Fuel Pump. If it Holds Vacuum, then it is Good. If Not, then the Diaphragm is Busted and the Pump Requires Replacing. If the Fuel Pump is Good, then Check the Crankcase Oil for Gas Contamination.
>>If the Crankcase Oil is Contaminated, then Drain and Refill the Crankcase Oil with Fresh Oil.
3- **If the Mower has a Manual Gas Shut Off Valve: Check the Manual Cut Off Valve and Make Sure it is Cutting Off the Gas Flow to the Carburetor. A- If Not Stopping the Gas Flow, then Replace the Valve. B- If the Mower Does Not have a Manual Cut Off Valve: Install a Manual Cut Off Valve and Turn Off the Gas Flow when the Engine is Not in Use. These Carburetor Styles Tend to Allow Gas to Seep by the Rubber Tipped Needle Kit or the 2 Pc O-Ring Needle Kit. A I Believe I Said Before, I have Seen a Lot of these Problems and this is the Way I have Found to be Sure the Crankcase Oil Does Not become Contaminated with Gas Again.**
>>4- If the Valve is Good or has Been Installed, then Remove the Cylinder Head. On the OHV Engines the Head gasket will Blow Between the Cylinder and the Push Tube Galley. This Allow Oil to be Sucked Into the Cylinder from the Crankcase and the Extra Oil is Just Enough to Cause the White Smoke.
>>5- Check the Crankcase Breather and Make Sure it is Clean and Operating Properly.
>>6- If the Crankcase Breather Sticks, then Oil is Pulled from the Crankcase into the Carburetor Throat and this Causes the White Smoke.
>>7- If the Crankcase Oil is Good, then Check the Gas Tank Cap and Ensure it is Venting the Tank. If the Gas Cap is Not Venting the Tank, then Pressure Builds in the Tank and the Pressure Pushes Gas by the Carburetor Float Needle Valve and Floods the Engine and Crankcase Oil.
>>8- On OHV Engines, Some of my Questioners have Responded Back to me then when the Head Gasket Blows between the Compression Chamber and the Valve Galley, or the Head Bolts Loosen, the Engine will Smoke Also. The Smoke is Usually a White to Bluish in Color Depending on the Extent of the Oil to Gas Ratio.
>>A Breakdown will Assist you in the Dis-assembly and Assembly of the Components.
>>To View a Breakdown of this Unit Go to this Site Addy, http://www.searspartsdirect.com/partsdirect/index.action?sid=PSHx20080114x00001 and Enter the Model Numbers 917-273280 and Click Search. From this Page you can View Diagrams and Parts Lists.
>>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. 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
