Xs650 inconsistent timing in left cylinder

WilliamJ

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I just finished rebuilding the top end of my 1977 Xs650d (Had a holed piston on left side).

it starts, right side is dialed in, but left side timing is either at the fire mark or closer to the top dead center Mark (see picture) going back and forth.

Any idea what would cause this? It seams to be firing closer to tdc than the fire mark.

i suspect this issue is what caused the holed piston, but have no idea what would cause this.

points are gapped.
dwell is at 90 (22.5 with meter set to 4cyl),
I sprayed brake cleaner on a rag and cleaned the points,
electrical connections seam fine.
I switched the plug wires and the issue remained on the left side.
I’m at a loss.

I just bought this bike and it’s my first motorcycle with points. It broke down 2 weeks after I bought it.

Thanks in advance for all your help!
 

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gggGary

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there is a separate plate so you can adjust both sides, if you run out of room before you get them correct and matched change the gap on one side to get the timing right, a few thousanths wide or narrow won't hurt anything.
 

5twins

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Are the points new or what came in the bike when you got it? I ask because sometimes an old points set can act funky, not dial in right because of wear.
 

nhsteve

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I had quite a bit of trouble static timing a '74 TX using "new" points. One side would be ok, but getting the other to get timed correctly and stay timed was frustrating. Finally I took the points off the plate, and looked at (with a magnifying glass) the small pivot pin and backside of the points. It appeared there was a 'hump' around the area of that pivot pin. I carefully flat filed around the pin (without altering it's diameter), and also the backside of the points in general. After remounting and setting things back again, the timing was repeatable and stable. After that experience I've always at least inspected the backside of any set of points I'm installing before doing any serious adjusting.

My :twocents:

Cheers!:cheers:
 

gggGary

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The OP gets this, but if you HAVE to fudge a bit, one side slightly retarded is much better than one side too far advanced.
 
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