QuestionThis is a Craftsman Model#:917.271051, Ser.#:050400B007281, with a Kohler CV15S(41596),Ser.#: YKVXS426GB, 15.5 HP. Runs and start fine cold. After about 15 minutes of mowing,(throttled up) the engine starts to surge then stalls. No re-start (cranks OK) until you wait about 5 minutes. Fuel tank removed and cleaned. Filter replaced. 1/4" fuel lines removed and looked through, ok. Carb removed and cleaned,(although no debris was found, all passage ways where cleaned with a small wire, carb cleaner, compressed air) Fuel shut off solenoid replaced ( rubber stop looked swollen, monitored voltage with LED, operates normal. LED goes off when key is turned off and when driver gets off of seat-safety) When it does stall, inductive timing light was attached and does flash when cranked. (new plug previously installed). Fuel cap was cleaned and vent in cap was checked with lite compressed air, OK. Able to make run by spraying carb cleaner into carb with air cleaner off, or by covering carb air intake, but won't run on full choke. When started there's no back fire or smoke from exhaust. Oil/filter has also been changed (10W30) Any thoughts? Valves hanging up?
AnswerFrank
Nowadays, a lot of mower/equipment is using OHV (OverHead Valve) style engines. This in itself causes many starting troubles. These engine use a compression release on the camshaft to allow for easy starting. Once the engine has started and reaches a speed of over 700 rpm, the weight on the compression release swings out and allows the engine to gain full compression and full power. After awhile, the valve lash/clearance begins to widen and the first thing that goes wrong is the compression release doesn't work properly causing the engine to drag which may sound to some as a dead or dying battery. I'm sure there are untold thousands of people that have replaced batteries, solenoids, starters, switches, etc., only to find themselves going to a repair shop and letting a trained mechanic do what is a simple maintenance adjustment. * Make sure any shutoff valve is open.
* Check for a clogged fuel filter, if there is one. There may be a sediment catching screen at the bottom of the tank as well.
* If your engine uses a primer bulb, does it feel like it is doing something? There is a distinctly different feel when it is actually squirting a little gas into the intake pipe. Check that the rubber hasn't deteriorated but if many pushes still doesn't do anything (and you're sure there is gas in the tank and the engine hasn't flooded from TOO MUCH gas), the carburetor and/or fuel line may need cleaning.
* If you are using gas from last season, discard it and start fresh. While old gas will usually work in an engine in good condition, this is not always the case, especially with one that has seen better days. The more volatile fractions evaporate leaving behind higher flash point gas. Why add another unknown factor to the puzzle?
* There may be water in the gas. If the carburetor has a drain plug, operate it to rid it of the bottom layer which would have the water. If there is no drain, repeated pulling on the starter cord should eventually clear any reasonable amount of water.
Once you have exhausted these obvious problems, determine if gas is reaching the cylinder as follows: Perform the normal starting sequence and then, assuming it shows no signs of wanting to start, immediately remove the spark plug. If fuel is reaching the cylinder, the spark plug should be damp with gas and there should be a very distinct odor of gas from the spark plug hole. If there is none, then there could still be a blockage in the fuel line or the carburetor may need cleaning. There can be numerous reasons for the engine to quit running when it gets up to operating temperature.. expansion of metal parts where bolts/screws aren't tight enough, breakdown of the condenser for the ignition points (if equipped), or a possibility of a crack somewhere. An overall inspection of the tightness of fasteners would be a good place to start.
* If the miss is a miss, the problem probably has to do with ignition or the fuel mixture. Check the tightness of the carburetor mounting bolts and where the intake manifold/air-fuel mix tube fastens to the engine block.
* If instead, the miss is popping through the exhaust, this might be caused by a bad exhaust valve or valve seat.
* If there is puffing or popping near the engine head, the head bolts might not be tight.
* If the engine spins over too freely when it's hot.. indicating much lower compression, check the torque of the head bolts.. if they were loose, the engine should now restart.
* If it won't restart until it's cooled down, the exhaust valve (and/or valve seat) may be the problem. If you can remove and disassemble the engine yourself, this isn't expensive to have corrected. If not, the shop labor for tear-down and reassembly will be fairly costly. A common reason for exhaust valve failure is that grass clippings become embedded in the cooling fins around the exhaust port area.
* If the engine is just failing to fire the spark plug when it's hot, there's a good chance that it's time to change the (points and) condenser. This can usually be confirmed by quickly removing the sp
