Small Engines (Lawn Mowers, etc.): Fluctuating engine, carburetor body, mixture settings

Question
Hi,

I have an Ariens Snow King 28", 11.5 horse snow blower. The engine is made by Tecumseh. It’s 2 -3 years old.

The problem is that the engine speed fluctuates at medium to low idle. There are no adjustment screws that seem to help. There are only 3. One is for the governor (I think that's what it is), one that controls when the throttle starts to open when you move the lever up, and an other one at the bottom of the bowl with a spring (you can push it into the bowl and gas flows out).

I replaced the spark plug and checked that the screws are tight holding the carb and surrounding screws. I also put a fuel additive in that cleans the carb and takes care of water in the tank.

It runs smoothly at high, but the speed varies at mid to low idle, except under load. It does not fluctuate under load.

Any help or advice would be appreciated.

Thanks,
Mark


Answer
Hello Mark:

From the Description of the Carburetor and the Fact that there is a Screw in the Bowl with a Spring Around the Screw, Tells me that the Carburetor Air Mixture Settings are Off or the Carburetor Needs Cleaning. The Lower Screw (High RPM Air Mixture Screw)in the Bowl Should Not Push in as you Stated. Try this First. Follow the Instructions that follow. Do Not Clean the Carburetor Unless Setting the Air Mixture Screws Does Not Help the Engines Operation. ****All the Carburetor Adjustments are the Same for Lawn Mower and Trimmers. There are Several Location for the Air Mixture Screws. The Idle Air Mixture Screws are Usually Located at the Top of the Carburetor Bowl and the Top of the Carburetor Body. If the Main Air and Idle Air Mixture Screws are Side by Side on the Side of the Carburetor, then the Idle Air is the Farthest from the Engine. The Main Jet Air Mixture Screw is Located in the Bottom of the Carburetor Bowl or Beside the Idle Air Screw on the Side of the Carburetor Body. Some of the Older Model Carburetors have the Main Jet Mixture Screw Straight in from the Top of the Carburetor Body (this is Rare anymore). If you have Cleaned the Carburetor (Disassembled and Soaked Overnight in Carburetor Cleaner (I Use Gunk). Then Blow Out the Passages with Compressed Air and Install a New Kit if Required. Now Setting the Air Mixture Screws:  ****Turn the Idle Air and ****Main Air Mixture Screws In Until SNUG **Do Not Jam** Then Reverse Both Screws 1 1/2 Turns. Holding the Throttle Full Open, Start the Engine. Turn the Main Air Mixture Screw Clockwise Until Proper Revs are Obtained. 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 Mixture Screw so there is No Hesitation when Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.**** Since this is a Tecumseh Engine, I have a PDF Site Addy that May Assist you Also. http://www.tecumsehpower.com/CustomerService/BSI.pdf You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.outdoordistributors.com/ and Select the T. Then Select Tecumseh. Then Select Don't have Part Numbers. Then Enter the Model Numbers. Then Select your Model and Download the File for Online Viewing. 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. Have 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. Thanks.

Respectfully

John