Issue only in first gear and only underload??

If it is a lean carburetor setting ..driving can be problematic overheating -- one way is to inspect the Plugs after driving a While in First Gear only
+ post pictures
 
Ok, I got this one. I bought a 1976 XS650 a few years ago, and I went through it (carbs, clutch, brakes, master cylinders, calipers, new battery, etc, etc) and on the maiden voyage, what Manbearpig1 describes is precisely what it did. I checked all the parts of the shifting mechanism, made sure the pawl at the shift drum was equidistant from the two nearest pins, checked the drive sprockets, the clutch, including the plates, thrust bearing, washers (they were not in the right order) and everything else I could think of that could possibly cause the problem. I knew down deep what it was, but I had to do my due diligence so as not to miss something simple. And the gearbox didn't clunk when it happened.
I eventually pulled the engine and split the cases, and lo and behold, the engagement dogs for first gear and the pockets they slot into were rounded off. Apparently, a PO had done some neutral drops and wore them off. The kicker is that someone had been in there with a die grinder and tried to smooth out the chips and burrs, probably making it worse. Also, the shift fork was well worn from the abuse. I have several donor engines around and replaced the damaged parts, and while I was in there, I ordered an overdrive 5th gear from MikesXS and installed it. Photos of the damaged parts included, with a pic of the innards of the gearbox.
Reassembled everything and problem solved - I got to put 500 or so miles on it before I put it away for the winter, with no issues from the gearbox whatsoever, with the bonus of a much more reasonable ratio for high gear without having to change sprockets and making 1st through 4th taller.
 

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Ok, I got this one. I bought a 1976 XS650 a few years ago, and I went through it (carbs, clutch, brakes, master cylinders, calipers, new battery, etc, etc) and on the maiden voyage, what Manbearpig1 describes is precisely what it did. I checked all the parts of the shifting mechanism, made sure the pawl at the shift drum was equidistant from the two nearest pins, checked the drive sprockets, the clutch, including the plates, thrust bearing, washers (they were not in the right order) and everything else I could think of that could possibly cause the problem. I knew down deep what it was, but I had to do my due diligence so as not to miss something simple. And the gearbox didn't clunk when it happened.
I eventually pulled the engine and split the cases, and lo and behold, the engagement dogs for first gear and the pockets they slot into were rounded off. Apparently, a PO had done some neutral drops and wore them off. The kicker is that someone had been in there with a die grinder and tried to smooth out the chips and burrs, probably making it worse. Also, the shift fork was well worn from the abuse. I have several donor engines around and replaced the damaged parts, and while I was in there, I ordered an overdrive 5th gear from MikesXS and installed it. Photos of the damaged parts included, with a pic of the innards of the gearbox.
Reassembled everything and problem solved - I got to put 500 or so miles on it before I put it away for the winter, with no issues from the gearbox whatsoever, with the bonus of a much more reasonable ratio for high gear without having to change sprockets and making 1st through 4th taller.

Thank You Sir -- And that one shifted Without Clonking going In and Out ---- Do I understand that part right.
 
Thank You Sir -- And that one shifted Without Clonking going In and Out ---- Do I understand that part right.
Yes sir. That's what threw me at first, it made no sound. It was more of a skipping feeling - just the feeling that someone was pulling in the clutch and then releasing it immediately every 10 or 15 feet. Even my wife could hear it in the house and thought it was me just horsing on it - blipping the throttle. I would expect the "clunk" sound you hear when putting it into gear from neutral. But I guess the damping of the oil and the fact it would skip just one dog, rather than crunching across a dozen or more pockets when shifting into gear, plus the sound of the engine under load masked it? Just spitballing here. Wagging? (Wild-ass guessing!)
 
Yeah, maybe you'll not be so quick to call me a liar, next time.
Back in the ignore bin with you.

Yeah well sometimes one gets it Wrong and other times one gets it Wrong again.
I have not called anyone a liar .Unless I know it is so. It happens -- But not this time.
I have a Motorcycle with worn dogs that is making nasty sounds putting it into First Gear
Going up or down Need to be careful.
In a process of finding solutions different views comes up .. Nothing personal Nothing to be upset about
 
Well if it was a clutch problem I would expect it to be worse in the higher gears. Are you sure it's not jumping out of gear when this happens? Hard to really diagnose from a distance but I would probably start by cheking things related to the shifting mechanism. Maybe the shift cam and the screw that holds the detent pins to it.

Not sure if those terms are correct but there is a star shaped retainer that holds the pins in and has a long screw that holds the assembly on the end of the shift cam. I had one or two bikes that had a shift problem that was traced to the long screw either breaking of coming loose.
Can you post a picture of the long screw?
 
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