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Any chance there is some slop in the shift linkage.
A lot of vibration combined with a low idle and loose gear box could drop into gear if everything is just right.
what model of bike. i use to hit my jockey shifter with my leg once in awhile and knock it in gear, but a newer bike should not do this unless it was not all the way in neutral.
A few years back, I was adjusting the idle on my '81 Ironhead chopper. Bike was on the kickstand, facing the back door of the house, idling in neutral. I was on one knee at the right side of the bike. I turned the idle adjusting screw, then reached up and gave it a bit of throttle to check it. The bike jumped into gear and shot forward, dragging me along. Since the bike had been leaning left on the kickstand, dragging me on the right side kept it upright. Of course, since my only hand on the bike was on the throttle, dragging me just gave it more speed. The front tire had been about six foot from the back door when we started, I managed to let go of the throttle about the time the front tire hit the door.
The door popped open, and the bike came to a stop when the handlebars wedged into each side of the doorframe. The engine died with the bike stuck upright in the doorframe. I was able to pull the bike out with only minor scuffs on the handlebars, the doorframe didn't fare so well. I don't trust neutral anymore...
About 5 years ago was in California Harley-Davidson and one of the salesmen told me about how he and a prospective buyer were looking at a bagger and asked that it be fired up. Salesman puts it in neutral, fires it up, bike slips into gear and crashes into the raised dais display thing. The salesman was laughing about it but at the time he and the buyer (scared sh**less non-buyer now) thought they were in trouble. Harley did an "investigation" and apparently it happens every now and then...chalked it up to a tight clutch.
Any chance there is some slop in the shift linkage.
A lot of vibration combined with a low idle and loose gear box could drop into gear if everything is just right.
That's what I was thinking. Only thing to add in is the weight of the shift lever. The heavier the lever the more ability to drop itself down into 1st gear.
I've been a little spooked of mine doing this from the get-go. I'm used to metric bikes that buzz, not flap their engines around. And their shift levers are tiny light weight things, not the massive pieces Harley uses.
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