I have had a slow leisurely project 1981 xs400 for the last two years. Purchased it non running, and slowly went through electrical system, carbs, and petcock. It starts/idles fine but the right cylinder runs way hotter than the left. With an infra-red thermometer the right header pipe (right next to the head) will be at 200+ degrees within 2 minutes, and nearly 500 Fahrenheit after idling for 5 minutes. Comparatively the left side will be around 90 degrees after 2 minutes and 140-160 after 5 minutes of idling.
Several months ago I rebuilt the petcock, replaced the float needles, the float o-rings, moved to 145 main jets and 45 pilot jets. Stock Mikuni bs34 carbs, but with MikesXS filters. If i had the original airbox I would use it, but I never had it. This got it running okay. It had no voltage so I rewired the stator, built a new rectifier and switched to a small sealed AGM battery. The electric start motor didn't work so I removed it and the starter clutch, so it is kick only.
In the last month I have:
Soaked carbs in berrymans & blown out all passages with compressed air
Synced carbs (with a homemade manometer & a snazzy Tecmate TS-81 VacuumMate)
Adjusted floats
Replaced pilot screw o-rings
Swapped ignition coils to opposite sides
Swapped carb diaphragms to opposite sides (problem has still stayed on the right cylinder)
Adjusted valves
Checked compression (155psi on left, 160psi on right)
This is really leaving me stumped (and frustrated) at this point. I haven't been riding it at all because I don't want to hurt the motor with it getting so hot but I have taken it on some 5-10 minute rides, 30-40mph max but am still unsure if it gets that hot just from idling or off the idle circuit as well. Once warm it seems to have a bit of popping 4k-6k, but it is hard to say which cylinder it is out of. By this point I am assuming the right cylinder.
One thing I didn't replace when I had the carbs apart for cleaning was the throttle shaft seals. Part of me is wondering if one is leaking air in, but I can turn the right pilot screw out to 4.5 turns and it still gets just as hot. Sometimes it smokes a bit. Also, I have discovered that a new exhaust gasket didn't seal and lo and behold it is on the right cylinder. Would that cause all of this?
If you guys have any advice I would really appreciate it.
Cheers,
Thaddaeus
Several months ago I rebuilt the petcock, replaced the float needles, the float o-rings, moved to 145 main jets and 45 pilot jets. Stock Mikuni bs34 carbs, but with MikesXS filters. If i had the original airbox I would use it, but I never had it. This got it running okay. It had no voltage so I rewired the stator, built a new rectifier and switched to a small sealed AGM battery. The electric start motor didn't work so I removed it and the starter clutch, so it is kick only.
In the last month I have:
Soaked carbs in berrymans & blown out all passages with compressed air
Synced carbs (with a homemade manometer & a snazzy Tecmate TS-81 VacuumMate)
Adjusted floats
Replaced pilot screw o-rings
Swapped ignition coils to opposite sides
Swapped carb diaphragms to opposite sides (problem has still stayed on the right cylinder)
Adjusted valves
Checked compression (155psi on left, 160psi on right)
This is really leaving me stumped (and frustrated) at this point. I haven't been riding it at all because I don't want to hurt the motor with it getting so hot but I have taken it on some 5-10 minute rides, 30-40mph max but am still unsure if it gets that hot just from idling or off the idle circuit as well. Once warm it seems to have a bit of popping 4k-6k, but it is hard to say which cylinder it is out of. By this point I am assuming the right cylinder.
One thing I didn't replace when I had the carbs apart for cleaning was the throttle shaft seals. Part of me is wondering if one is leaking air in, but I can turn the right pilot screw out to 4.5 turns and it still gets just as hot. Sometimes it smokes a bit. Also, I have discovered that a new exhaust gasket didn't seal and lo and behold it is on the right cylinder. Would that cause all of this?
If you guys have any advice I would really appreciate it.
Cheers,
Thaddaeus