1980 SOHC non points timing seems to change after applying throttle

philip skeps

XS400 New Member
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Lakeville, MN
Hello, I am very new to working on bikes and decided it would be a good idea to pick up a yamaha xs 400 that was currently in shambles. I was able to get the bike running and check the timing dynamically as described in the manual and found the timing was too far retarded (in between LF and LT is retarded right, i'm still trying to figure out terminology and stuff like that). I was able to adjust the timing by turning the non points plate until I was strobing at the LF mark. As soon as I layed on the throttle and let it return to idle the timing seemed to either advance or retard inconsistently. When I would lay on the throttle again it would match back up to the LF mark. Could my cam chain be slipping? Could my TCI be on its way out? I still receive good whiteish blue spark.

Along with this issue my bike hates to start while warm and seems as soon as I give it any throttle the bike will die when warm. I am unable to gun the throttle at any temperature most of the time but it seems to be able to do this when the timing is set correctly.

Any help is appreciated and please let me know if you need any more information or maybe even pictures.

oops forgot to mention that I also backfire through my left exhaust consistently and through my carbs occasionally