Craftsman Mower No Start - Backfire Thru Muffler
Dennis Gillaspie
7 years ago
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ssewalk1
7 years agolast modified: 7 years agoDennis Gillaspie
7 years agoRelated Discussions
Craftsman riding mower won't start
Comments (9)Pull the valve cover and check the valve clearances. The engine not wanting to crank over may be due to valves needing adjustment to restore function of compression release. Don't worry about the flywheel key shearing, that is not something likely to occur on a mower that has a belt driven deck, The concern over shearing a flywheel key by hitting something and stopping the blades is only true in push mowers where the blade mounts directly to the crankshaft. Belt driven blades can't stop the crankshaft quick enough to shear a flywheel key. The puzzling part of the description is how the exhaust seems to have gotten louder just prior to backfiring. Start with the valves....See MoreCraftsman Tractor Blowing Smoke, Backfiring, and Runing Poorly
Comments (9)"Does Kerosene burn hotter than gasoline?" Well.......yes, but just barely. The real issue about kerosene (as a fuel in IC Engines) is the violently explosive manner in which the kerosene "combusts" after being compressed and spark ignited. The gasoline formulae are all blended to perform at a specific "Octane rating" (which relates to the "rate of burning" of that fuel blend). Higher Octane rated gasoline burns SLOWER than low Octane rated gasoline. The octane rating specifications of motor fuels are based around the design parameters of the engines which will be burning the fuel. One of the primary considerations in fueling internal combustion engines, is to make sure that the fuel combustion is not violent enough to damage the combustion chamber components of the engine. With this aim in mind, gasoline is blend of various compounds and additives so that it does not actually EXPLODE in the combustion chamber, but instead it only "burns very rapidly". Kerosene, in contrast, is not formulated to be a fuel in the average, piston type, spark ignition ICE, and so DOES NOT contain any "Octane rating improvers" or "anti-knock" compunds. Consequently, when kerosene is used as a fuel in a piston type, spark ignition engine, detonation (instead of a rapid burn) will occur at the moment of the spark. Because the crankshaft and connecting rod (of a given cylinder) are nearly (but not quite) straight up, the detonation has the EFFECT of trying to force the crankshaft to stop and turn in the opposite direction. Because the reversal cannot actually happen, the effect of the detonation on the piston, rod, and crankshaft is very much like a fencepost being struck by a sledgehammer. The piston and all the other components of the engine were never intended to withstand the forces produced during detonation. For those interested in further reading, click the link below. There is a paragraph that deals with early attempts to use kerosene as a fuel in motor vehicles. It pretty much sums up what canguy posted. Here is a link that might be useful: Gasoline history...See MoreCraftsman 20HP Mower won't start
Comments (18)Think Timing... For power to be developed, the ignition of the compressed air/fuel mixture must take place at exactly the correct instant - just before the piston reaches Top Dead Center (TDC) on the compression stroke. Timing is set on older mowers with point type ignition systems by adjusting the point gap and generally only changes due to wear. However, these changes are gradual and unless the points come loose for some reason, will not likely suddenly prevent the mower from starting. On newer electronic ignition systems, there is basically no adjustment as the position of the electronic ignition coil/module fully determines ignition timing and this is fixed. However, timing can be grossly messed up if the flywheel key gets sheared and the flywheel then rotates a fraction of a turn on its mount on the crankshaft. The result may be a mower that does not start, backfires or runs erratically, lacks power, won't run and/or start when hot, etc. This is very likely to happen should the blade strike a rigid object causing the mower to stop instantly. In this case one or both of the blade lock key and flywheel key have sheared to (hopefully) protect the very expensive internal parts from damage. There are likely not going to be any timing marks for that old timing light you have sitting gathering dust somewhere. The only test really is to inspect the flywheel keyway to determine if damage has occurred....See MoreCraftsman LT1000 B&S 16.5Hp Backfiring
Comments (3)Thank you for including your "start up procedure" in your post. Good detail! But I still need to ask: Does the "backfire" sound like a loud blast from the muffler? or is it a more subdued noise like a loud "cough" back through the air intake components? And does the noise occur INSTEAD of the engine starting up (when you first turn the key) or does the noise occur after the engine starts........and when you remove the choke? If the backfire occurs when you remove the choke, you need to try removing the choke gradually over a period of about 15 or 20 seconds instead of removing it in one rapid stroke. Cold engines need a very rich fuel mix in order to get started. The choke accomplishes this by depriving the engine of most of the air wanting to rush into the intake when the engine begins turning. Because the choke is blocking the air flow, the mixture of fuel & air entering the engine is at this point "mostly fuel"....and that is what the cold combustion chamber needs to sustain combustion. Removing the choke before the combustion chamber has warmed (and it warms up in about 30 seconds) enough to sustain the combustion process can cause the mix to become very lean because there is a slight delay in the fuel flow out of the carb increasing to match the increased air flow when the choke is thrown open suddenly. Unless the engine is showing a lot of power loss under heavy load conditions, there is no reason to think this might be due to the carburetor needing to be cleaned or other reasons. Try gradually removing the choke and see if the engine behaves....See MoreDennis Gillaspie
7 years agoDennis Gillaspie
7 years agossewalk1
7 years agolast modified: 7 years agoDennis Gillaspie
7 years ago
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