1979 XS 650 idles fine , falls flat just off idle, carb is clean.

The cam has a couple bushings in each end for the advance rod to ride in. The outside bushing should have grooves cut into it's I.D. .....

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They are there to retain grease and provide a reservoir of lube for the advance rod. Clean any old hardened grease out and pack them with fresh stuff. The factory shop manual recommends a moly grease of some sort .....

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The manuals make no mention of it but servicing (cleaning and lubing) the advance rod and it's bushings is a required maintenance task. Do it as shown above and it will last a long, long time, a good 5 years at least.
How do you remove the plate that has the spring posts on it, I was able to figure out how to remove the other pieces but I got stuck on that one. Do you have a source for replacement springs that are the appropriate strength?
 

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Once you remove that notched ring, the advance unit backing plate should just slide off the end of the cam. But, being that all these parts are just raw steel, there's a good chance things are rusted together. Put some penetrating oil on there and let it soak overnight. Then, warming the area up with a heat gun may help. Mine was a bit stuck on there the first time I tried to remove it. I anti-seized the end of the cam when I put the advance unit back on and now it slides off nice and easy.
 
The best springs are originals but they're not available anymore. However, they do come up on eBay from time to time, so I'd start watching. But, if you grease up those bushings real good, your current springs may be fine. If not, and you're going to clip them, only do one to start as that may be enough. You don't want to make it too stiff or it won't advance properly.
 
My experience is that a malfunction of the auto advance system does not cause the symptoms as described ninitially by Prisondawg
The usual consequences of a faulty auto advance are kickback when starting, sluggish acceleration or revs not falling to tickover when releasing the throttle.
 
Hello. I swear the carb is clean. Not only did I meticulously clean them, but I bought an ultra sonic cleaner.

I will say the exhaust has a strong fuel odor, so i am thinking the fuel isn't igniting in the cylinder, I think it might be electronic in nature.

Perhaps the coils are worn out and the spark is weak? I have replaced the spark plugs.

Timing seems to be good at idle. I checked with a timing light.

Could this be a valve clearance issue? I have not checked this yet.
recheck your float height. also check fuel/air screws .it's running too rich.
 
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