nebojsa_o
XS400 New Member
Hi everyone. I am working on my girlfriends '79 XS400. She bought it about a month back. I rode it home for her as she didn't have her licence. The bike died on me at a red light after about 3 minutes of riding (but not during the 5 minute test ride... haha). After a few attempts I got it started again. Rode for about 10 kms at 100 and 110 km/h with no issues, and it died again when I clutched in approaching a red light. Luckily I was still rolling, so I dumped the clutch and it started up. Idle was low, about 800 rpms, so I kept it alive with the throttle, and got it home.
After a lot or reading on the forum here, I cleaned the carbs which didn't look bad. Checked the floats, and they seemed to be in spec with what I've seen here. When I reassembled, I turned the mixture screws out to 3 turns based on what I've read. They were at 1 1/4 turns. Bike started and idled great right from the start. While I was cleaning it up I started it a few times for giggles, and it started popping and idling weird just in the garage. Further research, syncing carbs is important, so I made a manometer and synced it. It was way off. Popping went away, idle is great again. I took it for a test ride, and it seemed a little slower than I remembered, wouldn't go over 6000 rpms, and in 6th gear at 80 km/h, holding 5000 rpms steady. Doesn't go further. It no longer stalls when warm though. I checked the spark plugs, and they were black. Cleaned them up a bit, adjusted the mixture screws to 2 turns, and tried again. Bike seemd a little better, but the same limit at 5000 rpms in 6th gear. I went to 1 1/2 turns, and then back to 1 1/4 turns. Balancing after each modification. Bike feels a lot better now at 1 1/4, revs quicker, and the rpms don't hang, so not lean. Plugs are not as black, but they are still dirty from before, so I'm thinking new plugs won't hurt. I'm still limited at 5000 rpms and 80 km/h...
On the last test ride, the bike pulled to 7000 rpms in lower gears. I clutched in while rolling and tried revving it up, and it went to 7000 paused for literally 1 second, and then went from 7000 to 9000 which is when I let off.
The bike has factory air boxes, factory exhaust. Compression is 145 and 150 psi. I didn't check valves and timing yet because I don't want to introduce any more of my own error. I know that hasn't changed since I first rode it at which point it had no issues going over 80 km/h so I'm guessing it's just a carb thing.
I did adjust the clutch as it was awfully hard to pull. Cleaned up the screw, greased it up, and adjusted it, and it feels great now. It shouldn't have anything to do with my problem I don't think, but I could be wrong.
Sorry this turned out so long, I'm just trying to give a lot of info, to maybe make your diagnostics easier. I am leaning towards cleaning the carbs again, but before I pull them apart, any pointers at what I should pay extra attention to? Also for what it's worth, the gas tank is coated inside with some sort of paint, so there is no rust or anything like that inside. Thanks for the advice in advance!
After a lot or reading on the forum here, I cleaned the carbs which didn't look bad. Checked the floats, and they seemed to be in spec with what I've seen here. When I reassembled, I turned the mixture screws out to 3 turns based on what I've read. They were at 1 1/4 turns. Bike started and idled great right from the start. While I was cleaning it up I started it a few times for giggles, and it started popping and idling weird just in the garage. Further research, syncing carbs is important, so I made a manometer and synced it. It was way off. Popping went away, idle is great again. I took it for a test ride, and it seemed a little slower than I remembered, wouldn't go over 6000 rpms, and in 6th gear at 80 km/h, holding 5000 rpms steady. Doesn't go further. It no longer stalls when warm though. I checked the spark plugs, and they were black. Cleaned them up a bit, adjusted the mixture screws to 2 turns, and tried again. Bike seemd a little better, but the same limit at 5000 rpms in 6th gear. I went to 1 1/2 turns, and then back to 1 1/4 turns. Balancing after each modification. Bike feels a lot better now at 1 1/4, revs quicker, and the rpms don't hang, so not lean. Plugs are not as black, but they are still dirty from before, so I'm thinking new plugs won't hurt. I'm still limited at 5000 rpms and 80 km/h...
On the last test ride, the bike pulled to 7000 rpms in lower gears. I clutched in while rolling and tried revving it up, and it went to 7000 paused for literally 1 second, and then went from 7000 to 9000 which is when I let off.
The bike has factory air boxes, factory exhaust. Compression is 145 and 150 psi. I didn't check valves and timing yet because I don't want to introduce any more of my own error. I know that hasn't changed since I first rode it at which point it had no issues going over 80 km/h so I'm guessing it's just a carb thing.
I did adjust the clutch as it was awfully hard to pull. Cleaned up the screw, greased it up, and adjusted it, and it feels great now. It shouldn't have anything to do with my problem I don't think, but I could be wrong.
Sorry this turned out so long, I'm just trying to give a lot of info, to maybe make your diagnostics easier. I am leaning towards cleaning the carbs again, but before I pull them apart, any pointers at what I should pay extra attention to? Also for what it's worth, the gas tank is coated inside with some sort of paint, so there is no rust or anything like that inside. Thanks for the advice in advance!
