1981 Yamaha XS400H Won't Start


XS400 New Member
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United States
Hello everyone. I have read through a couple of the other threads about the XS400 not starting, but I can't seems to find anything that helps my situation. The PO said that it used to run fine until the carbs starting leaking. He put a new set of carbs on it and tried making it into a bobber and lost interest. I tried to start it the other day and it would not start. It pops and backfires, but will not run. Could it be the timing? In the manual it says that the timing of this model doesn't need to be adjusted unless the pickup unit is taken off. Should I check the valve clearance? Any help is appreciated, thank you!

EDIT: The backfiring and pops are happening in the exhaust and coming out of the intake as well, if that brings for more information.

UPDATE: I rebuilt the OE carbs and put the OE intake boots on, left the pod filters on. Still didn't Starr. As a last resort, I swapped the pigtails for the coils, and it fired up instantly from the e-start.
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Are you sure they are correct carbs? Or that the carbs are any good?

Do you have originals?

Yes, I have the originals. They are the Mikuni KOGYO I believe. I just ordered a rebuild kit last night for them and am planning on cleaning them up. The carbs that are currently on it are the SWR 32mm ones from MikesXS. I set the valve clearance last night. The exhaust valves needed turned out about 1.5 turns each. I haven't tried starting it yet since. Also, the backfiring is happening in the exhaust and the intake.