Hi, agp47, I'm glad you got yer mower running due to the advice about junk in the gas. I am working through some issues with my Gravely ZT 50" mower with a Briggs & Stratton 16.5 HP twin-V OHV. Going on 10 years, I can say that it has been mostly trouble-free for that period. Maintenance has been minimal, keep the oil full and change it each season. I "usually" drain the gas tank for off season and run the engine dry to keep carb from gumming. Had to replace the (2) damper controls after about 5 years. They are the thin struts or "shock absorber" looking things that attach to the steering bars. You know they are shot when get rocked forward and back in you seat like a rag doll.
I recently got two symptoms with the engine that remain a mystery and which I fixed just by messing with it till it started. Symptom #1 was no gas to the cylinders, the spark plugs remained "dry" and engine cranked and cranked but wouldn't run. Fuel and filter were clean, fuel pump made a little stream of gas when unhooking its hose to the float and bowl. Finally discovered that for an unknown reason, the wire running to the fuel solenoid (attaches to float bowl) was "dead" (no 12 volts) while cranking. Furthermore, the hot wire to the fuel solenoid showed continuity to ground when I expected it to be an open circuit when all is off. I now suspect that I have a short created by insulation worn off of the solenoid hot wire where it rubs the engine cooling fins somewhere. Moving, jostling the wire magically fixed the symptom, but I am getting occasional misfires when the engine runs, suggesting it may still be grounding intermittently as engine vibrates.
Symptom #2 was no spark to the plugs. I followed a Youtube by "Taryl Fixes All", a funny guy with buck teeth prop, but he's very knowledgeable and helpful. Taryl saved me some bucks, teaching me how to check the magneto coils and the inline diodes in the wires feeding those coils. The diodes (two because of the twin-V) checked out at 0.55 ohms each and measured this in only one direction as they should. The magneto coils (some call ignition modules, or armatures) also checked OK, measuring 4.34 ohms between base and plug boot and 4.43 ohms between kill terminal tab and plug boot. It was as if the kill wire was grounded, say from terminal "M" to ground in the key switch. I am concluding that the issue was with the Start relay which went away when I swapped out the PTO relay and Start relay. They are interchangeable literally "black" boxes about 1 inch cube. I have replaced both handfuls of times. No clue why the swapped relay acted "proper" in its PTO relay role because blades should not have turned if the relay was bad.
Gotta reminisce a bit. Some of you might remember my sad story of when my Troybilt Horse cultivator took the literal plunge and died. I left it running unattended once while trying to test it and it slipped into gear and plummeted down my storm cellar, head banging the exterior door and tiller blades grinding at the concrete steps. The brass worm gear I had just installed was ground into filings. The sounds were horrific and mournful and I felt like the captain going down with his ship.
Well, another more humorous story was the sudden screeching stop of a small tractor-like mower that came from one of those popular stores where you buy stuff out of a box, no support, no dealership. It was one of those cheap yard tractors with undersized engines (and mower deck barely larger than the self push variety) that you run into the ground like many similarly cheap push mowers. After the loud screech there was no power to anything, just a free running motor. Long story short, the bolts that fasten the engine to the chassis had "all" fallen out and the mere tension of the drive belts pulled the engine back till the PTO shaft rubbed the chassis. A kind neighbor gave me fine-threaded machine bolts to replace them and all was back in business when the belts were fitted on the remounted engine pulleys.
