1980 XS400 Wont rev out past 4k


XS400 Member
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Nashville TN
Hello! I've got a 1980 xs400 that I'm almost done with but I took it for its maiden voyage today and it won't rev past like 4000 rpm. Carbs are clean using stock jetting and air boxes with new filters and everything. I'm wondering if it's not an ignition issue. It seems to only have trouble under load. It does pretty well in neutral. Maybe it's not getting the advance going? It's the electronic ignition version so no points to adjust but I also haven't hooked the neutral light or any gauges up yet so maybe the CDI doesn't know it's under load and isn't advancing timing just because that? Idk what do you guys think? Thanks!
Could very well be the timing or the advance, but that is pretty easy to check. Put a timing light on the left plug wire and pull the timing window cover (3-4" round cover) on the left side case. With the bike running, you should see the tick mark to the right of "LF" in the window with the timing light which represents 10deg BTDC. Rev the bike and you should see the timing advance up through the timing marks and end up at 30-40deg BTDC at or above 3000rpm.
Starter chain 2.JPG

The electrical stuff you have not hooked up will not impact the timing. If the timing doesn't advance then the TDI or the pickup coil signal could be to blame.
Gotcha. I did check it with a timing light and it's dead on LF at idle but I haven't checked it at different RPMs yet to check the advance. Got the neutral and oil pressure lights hooked up today but haven't had a chance to start it since.