Small Engines (Lawn Mowers, etc.): INTEK 18.5 HP problem with speed control, throttle shaft, shaft seal

Question
Craftsman 18.5 hp INTEK PLUS Briggs Engine, Model # 31P777, Type # 0348-E1. with Family Code: YBSXS.5012VP  274826 on engine tag. (42" Lawn Tractor, Model 917.273638)   Engine runs at about 3/4 speed with throttle lever set at minimum, (throttle valve closed).  Checked position of Throttle Valve, found to be closed with all linkages and springs to governor arm in place.  If engine is under load, blades engaged, then you have some control of the engine speed by using the throttle leaver. If you disengage blades, you have no control over engine speed, not even if you manually close throttle valve on carburetor.   Visually checked throttle valve, it is tight and appears to be functioning correctly.  Throttle shaft Seal appears to be in good condition.  Also checked for cracks or leaking gaskets in manifold/carburetor, all looks good.  Governor also appears to be functioning correctly.    Engine has approximately 86 hours run time.  Totally stumped and need help…  Symptoms make no sense to me as to the cause.   Any help would be greatly appreciated.  Thanks!!

Answer
Hello Danny:

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 and Enter the Model and Type Numbers. Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View. 1- Have you Removed the Carburetor Bowl and Checked the Welch Plug (Breakdown #127/A)? If the Welch Plug is Loose or has a Hole in it this will Occur. The Engine Pulls Gas that is Metered by the Size of the Leak in the Welch Plug into the Cylinder and Idle Can Not be Achieved. 2- Is the Throttle Valve Thru Shaft Attached Tightly to the Throttle Plate? Sometimes the Plate will Loosen from the Shaft and When the Plate Shows the Engine is at Idle; the Throttle Valve is Actually Open. Hold the Throttle Valve (Breakdown #130) and Try to Move the Throttle Valve Using the Throttle Plate (Breakdown #131 *Note: The Throttle Plate and Thru Shaft are One Component in the Breakdown and Usually are Considered One Component Once Assembled at the Factory. Before they Are Assembled they are Two Components. The Older Engines had a Square Headed Thru Shaft and a Matching Throttle Plate. The Throttle Plate was Attached with a Screw and Flat Washer. This Design was Replaced with the New Rivet Fit. Sometimes this Fit will Loosen from Vibration and Allows Slip Between the Two. When this Happens, you have the Problem you Described.) 3- Is the Idle Adjustments (Breakdown #98) Correct? These are to Start with. Let me Think on it and I May have a Few More Suggestions. I Think I Covered All of The, but Prefer to be Consider it More. After I Finish Answering the Other Questions, I will Reconsider this and Follow Up if I Think of Anything I May have Left Out. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John

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Respectfully

John