Hi everyone I'm new here so please forgive me if I'm posting this thread in the wrong section. But I've recently bought a used lawn small ride on mower and up until recently I've had no issues. The machine has the 16hp Kohler engine fitted. I think it's original with only 300hrs on the meter.
As soon as I purchased this mower I gave it a service using genuine parts, the usual oil filter, air/fuel filter and oil etc. After the service the mower ran ok and I continued to mow the lawn.
My problems started the next time I mowed the lawn. (About 2wks later) The machine ran perfect for about an hour and then it started to loose power. I assumed it was running out of fuel so I limped it back to my shed for new fuel. But the fuel level was still ok in the tank. I started the engine and noticed that it wouldn't rev up. And that the idle speed was getting increasingly erratic. To the point that it was difficult to actually keep the engine running at all.
I'm a mechanic by trade but I don't have any experience working on these small engines. My first thoughts were the fuel pump. I removed this and manually operated the arm and there was a suction. So I fit it back to the engine. But when the pump was installed back on the engine and at idle speed the suction was very poor. I'm not sure how much pressure these small pumps operate at. So I called my local John Deere shop and they advised me that they have never sold a fuel pump for this engine model, so it may be very unlikely that's at fault. I removed the air cleaner and squirted a small amount of fuel down the carb intake whilst the engine was running but the revs did not increase . It sounded like I'd flooded the engine. I wonder if I'd put too much fuel down. So I began then and pulled off the carb, I blew out the carb using compressed air, removed and checked the float etc. jets looked ok and not blocked. I checked the operation of the solenoid fuel shut off at the base of the carb. All seem ok. So I checked for a spark. I pulled off the HT lead and found a very weak erratic spark when cranking. I attempted to test the coil using my meter but only got resistance readings between the spark plug HT lead and the outer coil that bolts to the engine. I got nothing from the centre terminal and HT lead so I figure this coil to be at fault. I purchased a new genuine coil and fitted it to the engine.
Still no better. So I looked further.
I removed the valve cover to make sure the rockers where moving. The appear to be ok. I did notice I've only got 5 to 6 vdc coming from the coil terminal when running. Not sure if this is good. I know nothing about magneto coils. I assumed I should of put 12vdc to the coil from the ignition like car 4 stroke engines but when I tried this the engine stopped running. The engine also still ran no difference with this terminal wire disconnected. I'm guessing the coil makes it's own spark in connection with the flywheel pick up.
Ive also checked the flywheel for looseness. It appears ok. I've also checked the coil/flywheel pick up is directly at piston TDC when opposite the coil. So I'm guessing the piston timing is ok. I've removed the new spark plug and refit the old one. Still no better. I did notice the spark plug is covered in black soot. This would lead me to believe a fuel issue. I removed the fuel pump once again and cranked the engine and I could see the cam lobe than pushes the fuel pump arm turning, so I'm assuming this is ok. I stripped down the fuel pump and the diaphragm is ok. I've also checked the fuel tank vent. That's ok.
Really at a loss as to what to try next. I know these engines are meant to be simple to maintain, I'm used to v8s. Lol. I think I've over looked something here. I might try a different batch of fuel and possibly replace the fuel lines and clamps. I have noticed that the spark from the new coil isn't much better than the old one. Anyone got any ideas on what to try next. I have noticed that when I moved my throttle lever to really low idle the engine then will idle very smoothly but when I go to increase the revs it just coughs and splutters and stalls. Also chuffed out black smoke from the exhaust. This once again would lead me to believe its fuel pressure related. Is there a way I can gravity feed the carb and bypass the fuel pump to test this theory? Any ideas or help would be greatly appreciated. Thanks.