QuestionQUESTION: I have a 1997 sears lawn tractor with a 13.5hp briggs and stratton engine. The mower starts and runs great (small puff of white smoke on start up) but when it when the engine gets hot ( about a half hour of use) the flow of fuel into the fuel filter slows and the engine stalls. The fuel filter is new and installed the correct way, i cleaned the carb and although its old it seems fairly clean. When the engine is started cool the fuel filter seems about half full, and when the engine is hot it starts to sputter and the fuel filter seems to be almost empty with only a small amount of fuel dripping in. if i disconnect the fuel line from the carb the fuel flows freely. thanks, Bill
ANSWER: Hello Bill:
Check the Crankcase Oil for Gas Contamination. If Contaminated, then the Carburetor Needle Valve is Not Seating Properly and Allowing the Gas to Flood the Engine when it is Not in Use. The Gas Seeps by the Rings and Contaminates the Crankcase Oil. This Thins the Oil More than Normal and Once the Engine Reaches a Certain Temperature the Engine Loses Vacuum and the Vacuum Fuel Pump Quits Operating. This Stops the Flow of Gas and the Engine Quits. The White Puff of Smoke on Start Up and the Description you Gave are Good Indicators of this. 1- If this is the Case, then The Following is an Instruction File I Made for this Repair. Any Input Concerning the File is Appreciated. Depending on the Engine Model, Usually the Gas in the Crankcase Oil or White 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, 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.** 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. 8- Some of these Mowers have a Pickup Tube. Remove the Pickup Tube and Ensure the Tube Screen/Filter is Clean and the Tank Does Not have Trash in it. 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. 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. Thanks.
Respectfully
John
---------- FOLLOW-UP ----------
QUESTION: I checked the crank case oil and there didnt appear to be any fuel mixed in with it. I changed the oil and used the mower. It starts right up, small puff of white smoke and then runs great for about a half hour and i can see there is less and less fuel going to the filter until its empty then the mower stalls. If i let it sit and cool down for about ten minutes the filter fills back up with fuel and is ready to go again till it gets hot. The fuel lines are not clogged and the carb seems clean. what should i try next? Thanks, BIll
ANSWER: Hi Bill:
What you Described is the Caused by the Gas Tank Cap Not Venting the Tank. A Vacuum Builds in the Tank and Restricts the Gas Flow to the Carburetor. After Setting the Vacuum Slowly Leaks Off and the Gas Flows to the Carburetor Again. Clean the Cap Vent Hole/s or Replace the Cap. 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. 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. Thanks.
Respectfully
John
---------- FOLLOW-UP ----------
QUESTION: hi, i put on a new gas cap and new fuel lines but still have the same problem. Mower runs great for about 40 min then looses fuel and dies. i did take off the float bowl after loosing fuel pressure and fuel started flowing to the filter again. i think i may try replace the float bowl gaskets. do you have any other suggestions? thanks for your time, Biill
AnswerHi Again Bill:
Does this Engine Use a Fuel Pump? If Yes, then Replace All the Spring Style Clamps with the Screw Style Clamps. Most of these Engine Use a Vacuum Operated Fuel Pump. When the Hoses get Old the SPring Style Clamps Loose their Tension and Dont Seal Properly and you Lose Vacuum to the Pump. 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. 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. Thanks.
Respectfully
John
