I am really tired today running between all the big box stores. At the end, I didn't option the lawn boy because I really can't justify the extra cost vs sears promo today. Plus, a technician at Rona's service center gave me a friendly warning about the Tecumseh engine, the supply of the parts might be good for next 2-3 years but can't promise anything at long run. I still have a thought that a good mower should last me 10 years ironed in my head... However, I really like the design of the lawn boy 10684, everything seems very well design and build quality is better than others. If it's around $350CND range and none self-propelled model, I would pull the trigger, no question ask. I went back to Sears and ordered the Craftsman 36933 model (3-in-1 with bag, side discharge, mulching), which has B&S 850 platinum engine (8.5 ft/lb torque), no choke and no primer needed. The price is just what I am aiming for, 289.99+taxes. The engine seems pretty well build but the rest of the parts are very standard, a regular every week lawn mower...

Air starvation is what I was indicating from your description of starts easier with the air filter off allowing adequate air to fuel mixture. As JL has advised dirty or loaded filter medium will cause this extreme condition. However as JL has requested (orientation) if the hose connects to the venturi area of the carb it will have a direct effect on air entrainment into the fuel air mixture. As we have stated previously , not having you engine at arms length make diagnosis rather difficult (hit & miss) . A torn or cracked or loose impulse line is something any technician inspects and replaces as a matter of fact. This from a former diesel mechanic who has chased numerous vacuum / return to tank fuel line issues causing air entrainment hard or no start diesel applications . Anyhow for what ever reason glad you have solved your hard starting dilemma :)

Read and re-read this carefully. It might seem complex to the novice but it is really a straight forward and in depth explanation of what goes on, and what you will be looking at. Remove the spark plug from each cylinder. You will adjust BOTH valves on "the same cylinder", ONLY AFTER THAT CYLINDER has been positioned to the proper point in the 4-stroke cycle. Remove the valve cover from both cylinders. Identify each valve as INTAKE valve or EXHAUST valve by doing a visual reference. The INTAKE valve will be physically closest to where the intak manifold connects to the head and the EXHAUST valve will be nearest to where the exhaust manifold connects to the head. Next you need to determine which direction the engine rotates when running. You can determine this by spinning the engine with the starter while watching the flywheel through the fan shroud. Mark the direction with an arrow (at least on a sketch if not on the engine). Once you have determined the direction of rotation, you can proceed to positioning the engine for valve adjustment. You should trun the engine by hand a few complete revolutions to familiarize yourself with the sequence of valve movements through the entire 4 stroke cycle. It requires two complete revolutions of the crankshaft (720 degrees of crankshaft rotation) to one complete "4 stroke cycle". The 4 strokes of a four cycle engine are (and in this sequence): (1) INTAKE STROKE (2) COMPRESSION STROKE (3) POWER STROKE (4) EXHAUST STROKE. The compression stroke is the stroke where you perform the valve adjustments. Before we try to figure out how to identify the compression stroke for a specific cylinder let's describe the movements of the valves and the terms used: When a pushrod is RISING and lifting a rocker arm, the rocker arm will be pushing a valve DOWN. When a valve is DOWN, it is OPEN. When a valve is UP, it is CLOSED. OK, turn the engine by hand in the correct direction of rotation while watching both valves of the cylinder you are going to adjust the valves on. When you get to a point in the turning where the INTAKE VALVE begins to rise up (closing) and the exhaust valve is already UP (closed), you are in the beginning of the COMPRESSION STROKE. At this time you need to insert a wooden pencil or a wooden dowel rod straight into the spark plug hole until it contacts the piston. Hold the dowel firmly against the piston with one hand and resume turning the engine with the other hand. Observe how the piston pushes the dowel out of the plug hole as the piston moves toward the magical point known as Top Dead Center (TDC). At the point where the dowel movement stops, mark the dowel flush with the edge of the plug hole. Now, measure upward 1/4 inch from that mark and put a second mark. Put the dowel back in the hole, firmly against the piston and slowly resume turning the engine (in the direction of rotatation) and you will see the dowel move into the hole as the piston drops. Continue turning the engine until the second mark on the dowel is flush with the edge of the spark plug hole. This cylinder is now in the correct position for adjusting the valves ON THIS CYLINDER ONLY. After adjusting the valves on this cylinder, you will need to repeat the entire procedure to get the opposite cylinder into position to adjust its valves.

***"My question is what is the route of the gasoline from the overflowing bowl to the engine internal when the engine is shut off? It cannot be through the jet especially the main jet since the solenoid shuts it."*** The fuel cut off solenoid (afterfire prevention) indeed cuts off the flow of fuel through the main jet. But the carburetor has another "fuel jet" besides the main jet. There is a much smaller fuel jet known by various names, "pilot jet", "idle fuel jet", "low speed jet", "slow jet", to mention some of the aliases. To understand why a solenoid valve is employed to shut off the main jet fuel flow.....but leave the pilot jet "uncontrolled", requires an explanation of the intent of the "main jet cut off solenoid", and the correct way to shut down a running engine equipped with a fuel cut off solenoid. The fuel solenoid is there to prevent "afterfire explosion" (also erroneously called BACKfire) from occuring in the exhaust system when shutting down a hot engine. Shutting down of engines on OPE was once accomplished by simply "turning off" the spark ignition system and allowing the engine to stop as a result of "no combustion because of no spark". In those days, shut down was usually punctuated by a loud BANG as the engine managed to "have the last word". Because the carburetor feeds fuel to the engine by "venturi effect", the fuel will continue to flow out of the carb bowl and into the intake>cylinder>exhaust system as long as the engine continues to spin. Without a spark in the combustion chamber, combustion does not occur, and so the unburned gasoline is run through the cylinder, heated up by compression and absorbsion of heat from the surfaces in the cylinder. Then this heated fuel/air mix is expelled from the cylinder into the exhaust system (which is also still very hot, you could even say it glows). So long as the engine is still turning, the fuel/air is moving too fast out the exhaust system for the fuel portion of the mix to absorb enough heat to "spontaneously ignite". At the moment the engine comes to a halt, the fuel/air mix stops moving also. At this point, the fuel/air charge is stationary inside the hot exhaust system, and begins to absorb heat from the hot spots of the metal surfaces. When just one tiny portion of this fuel/air charge reaches the ignition temperature of gasoline.......KABOOM!, or at least, bang. HOW TO SHUT DOWN AN ENGINE THAT FEATURES A FUEL SOLENOID: While the engine is running at 50% RPM or more, TURN OFF the ignition switch. This cuts the current feeding the fuel solenoid valve, and the valve closes to seal the main jet. The engine spark ignition system remains fully functioning and keeps right on sparking inside the combustion chamber. The pilot jet continues to feed its measly little bit of fuel into the carb throat while the engine continues to "wind down toward zero RPM". Because the throttle was left in the open position, the fuel/air mix afforded by the tiny pilot jet is much too lean to support normal combustion, so the engine continues toward stopping. This extremely "lean" mix actually purges any last dregs of fuel that may have come out of the main jet at the moment the solenoid closed the main jet. This is how the fuel solenoid operates to prevent "afterfire" if proper shut down technique is used. The fuel that "drowns" an engine overflows from the carburetor bowl through the pilot jet, which is not controlled by the fuel solenoid. Venting and venturi effect would require still more consumption of time and bandwidth, but I'm game if you are. It will just have to be later as I'm outta time for today. :^)