I have been struggling trying to figure this mower out! I have a 1987 4 cycle Toro self propelled mower Model 20692-serial # 7013173 Tecumseh engine model Tvs100-44011A. I have owned it for 13 years and have had no problems except replacing tires. It owes me nothing! About 2 months ago I would mow with it for 20-30min and it would spit and sputter briefly and then die. It would do this every time I would mow at about the same time. It would not restart until it cooled off. Once cool it would run like a champ for another 20-30min. I replaced the air filter and plug, oil, the fuel cap and replaced fuel but no help. It blows a little smoke but uses very little oil. I spoke with toro dealer and they felt confident it was the coil. I checked the spark when it acted up and it seemed to be intermittent. It did spark but it seemed to be weak to me. I replaced the coil and it mowed my yard the first time without a problem. The second time I mowed it began doing the same thing it did before. I did recheck the fire when it was acting up and it appears to be getting spark. It was a very cool day when I mowed the first time after replacing the coil. I thought maybe that was why it did not stall. I did a compression check, cold was 80psi and when hot near the same. The only thing I have not done is replace the fuel line. It is probably the original line and it is mushy feeling. It appears I will have to take off the intake/carb to get the line off. I was just wondering if it was vapor locking. The line travels right under the exhaust on the way to the carb. I felt if it was a carb issue why wouldn't it do it cold? I am going to check the spark again next time I mow and it acts up. I also had drained the fuel tank and cleaned it. I blew air in tank and line to carb. I have taken fuel cap off when spitting and sputtering with no help. I also pushed the primer when acting up and it did not act like that would pep it up. Any ideas are appreciated. I am close to pushing a new toro!
On a mower of that age I would check the small wire that goes to the coil for any sign of insulation rub-through. If that wire finds a ground circuit the engine will die as that is the kill wire. Next I would make the problem act up and if you have good spark, shoot a little carburetor cleaner in the carburetor (remove air filter first) and try restarting it immediately. If the engine starts on the carburetor cleaner and dies out a few seconds later I would suspect a fuel problem such as the fuel line as you already stated or the carburetor itself needs rebuilding.
