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This started with my KTM. Took it for a short road ride last week and discovered along the way that if I hammered the throttle it'd cut out on top as if I hit the kill switch. Well, the bike hadn't moved since some time last summer, same gas... gotta be bad fuel, right? So into the corner it went, tank drained.
This weekend I went to Canaan for the first time, and brought my motard. My first session out I heard it starting to detonate on top in 4th and 5th once warm, so into the pits, mixture richened, and when that didn't clean it up I tracked down a can of Sunoco 260GT to throw octane at the issue. Prior to this it had only been run at short tracks since rebuild, and never been wrung like this.
Well, that helped, no detonation and I was able to start trying to learn the track. Once I started to build a line I was finding out that my gearing was a lil short as I held it WFO for longer and longer. Guess what started to happen? Same symptom set, if wrung out in 5th it'd cut out. Close the throttle for a moment and it'd respond again. Ok, WTF, retired the machine for the day.
Come home, put clean, fresh gas in the KTM and it's doing it even sooner than before, 1/2 throttle is enough to piss it off so bad it'll actually stall out, requiring kicking to refire. Whatever is going on with one I suspect is going on with the other. I could believe a crank seal leak on the KTM due to inactivity. The motard absolutely has not sat this year. I also don't get why it literally shuts down until it's coasted for a moment with closed throttle, I would expect an air leak to recover quicker when the throttle closed? I would like to implicate the gas, but the motard is running from a fresh, previously unopened can of 206GT. I'm going to try and rig/beg/borrow/steal a setup to leak test both motors. In the mean time I've pulled the plug on the motard, it's reading a touch rich which I would expect given I purposely fattened it up, borescope says I didn't damage the piston or cylinder, and the only crank movement I can find is a touch in and out, no side to side / up and down. Brake and parts cleaner on the ignition side seal while the bike is idling doesn't do anything. Oil drained out, no signs of being down, no fuel smell, bike is not smoking excessively.
Does this symptom set ring a bell with anyone else?