Tops out at 40mph


XS400 New Member
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Hey guys new here first time posting I bought a 1980 xs400 for 350$ I got it running and riding but it tops out at 40mph 4th gear screaming I shift into 5th it starts coming back down till I shift back into 4th is that a transmission issue or top end?? This is my first bike so I'm not sure where to start.

Based on the little above, A check of cylinder compression would be good, but I would first clean the carbs. Clogged needle jets and main jets would limit your open throttle performance. At wide open throttle is the engine surging?
She will sputter and cough unless I slowly give it throttle and let it work it's way up I ran a small amount of seafoam threw it and it helped it idle and it seemed more responsive and makes it to 40 faster but still tops out at 40mph I just got a carb rebuild kit for both sides so I will start there thank you
I just got a carb rebuild kit for both sides so I will start there

Good call. It may be multiple things, but get the carb off of the list first. Other stuff like stuck rings might just work themselves out over some time, but a clogged carb usually is not one of those things. My bike was also $350 and it had a host of issues, so the fact that yours is running at this point means things are looking up. Let us know what happens after the carb work.