Same bike (1985 Husky 510 4-stroke), same person, two stupid things:
My buddy and I were going dirt riding in the late 80s. I unloaded my bike and tried to start it. I kicked and kicked and it wouldn't start (it usually took 1-2 kicks to start). We checked it over, pulled the plug, etc, and took turns trying to start it. We pulled the plug again, and checked for spark, we also checked for fuel in the float bowl. We kicked some more, and tried push starting it down a hill. I was ready to load it in the truck, when something told me to check the airbox. I opened it, removed the air filter, and extracted the rag I had stuffed in there while I washed the bike.
A number of us were riding in the woods, on a trail that had a few water crossings. Right past the first water crossing, we came across a couple of guys trying to start a drowned CR250. We stopped and helped them by holding the bike upside down, with no spark plug, while someone fanned the kick starter. After we got all the water out of the crankcase, we got it started, and continued on our way. A short distance later we came to a deep water crossing. Halfway through the engine on my Husky died. The current was trying to flip me over, so a few friends jumped-in to help me pull the bike to the other side. Once on dry land, I kicked and kicked, with no results. I pulled the plug, and checked the airbox. There was no evidence of water, and the spark was good. I put it all together, and we all took turns kicking, to no avail. As we were catching our breath, the 16 YO son of a friend pointed to my Husky and said, "Wow, European bikes are really strange. On most bikes the petcock is down for on, but on your Husky it's sideways for on." I walked over, turned the petcock handle down, waited a few seconds, and started it on the first kick. I had shut the petcock when we stopped to help the guy on the CR250, and forgot to turn it back on.