So this post will be missing some information simply because there are several things I'm not sure of. Bought an 85 K100 off a friend who purchased it a year ago. It had been converted into a cafe racer and has no guages whatsoever. He rode it for a few months and let it sit for roughly 9 months out in the elements. I got it off him, drained gas tank, added new gas and fuel injector cleaner and got it started and running well, firing on all cylinders. Was a bit of delay under sharp acceleration but otherwise it ran strong and got to speed very quickly. Went around the neighborhood on short rides, 15-20 min and all was well. Then after replacing the rear master cylinder I took it on a longer ride, roughly an hour. Was running great and then towards the end it started running rough, backfiring a bit and sputtering. Got it home and changed the plugs and fuel filter so far with no effect. Have a compression tester coming but I don't suspect that's the problem. It starts and runs fine but runs rough. Far from scientific but all 4 pipes get hot so I don't suspect a dead cylinder. I know there's a big lack of info but just hoping someone has had something similar happen and can give me some ideas.