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If both your pic's were taken at the same time without rotating the crank then the ATU position is good. Looking closely you can see the locating pin is at the top which is correct when its at TDC. Post #4 confirms in this thread...

Welcome & cool looking bike. One question though, are the forks braced? Note that the single sided disc can cause forks to twist under heavy braking. Standard bikes have some bracing built into the mudguards.

That first picture is where the light comes on? Thats very retarded, not advanced. Advanced is to the left of the F mark, remember the engine turns over anti-clockwise so advance is in front of the F, retarded is past (to the right) of the F. Picture of the points might help, have the gaps...

Very busy night last after a load of parts turned up yesterday. Firstly, fitted a new ATU and got the timing sorted, that’s in another thread. Next I got the carbs balanced (though they were very close to begin with) using a home made manometer. Checked the float levels using the clear tube...

Just to say thank you to everyone and to let you know that the new ATU (and other bits) turned up really quickly (for a change) and I fitted it last night. Interestingly after fitting the new ATU the timing was off, way too advanced and the dwell on the left cyl had dropped to 20 deg (RH cyl...

Is that beneath the LH side cover? - broken drive chain or something caught in the drive chain probably. As signal says it looks cosmetic.

Shame on Yamaha for not incorporating some method of adjusting them. Maybe drilling/tapping the stops and have an adjuster screw? Anyone tried?:sneaky:

Well, I've bit the bullet and ordered a new unit: https://yambits.co.uk/xs650-auto-advance-governor-unit-points-models-only-p-23821.html With a new one on the way I suppose tomorrow night I can start experimenting with shims, don't fancy trying to bend it and having it crack/break off while the...

A couple more pictures, timing is set above F mark if it goes much further towards T it splutters at idle (1200rpm). At 3,000+ rpm the advance goes to about where the second picture shows.

Both cylinders are already retarded by a fair bit, firing directly above the F mark. If I retard much further it starts spluttering. Dwell meter says gaps are 22.5, When revved to 3,000 the timing mark goes way past the advance mark.

Finally sorted the misfire on decel but a new problem has risen when doing dynamic timing. The timing advance goes well past the advance mark. I’ve read through dozens of threads on the subject but haven’t found what I think may be the problem. Doesn’t seem to be much wear in the bob weights...

There is an alternative way of adjusting the valves by rotating the engine to find when the gap is largest and adjusting it at that point; Not sure why this link is not working but you can search for Yamaha XS650 valve adjustment made easy by Lanny Mobley I did my valve clearances last night...

Thanks Jim, makes perfect sense now. Told you its been one of those nights, my brain is not firing on all cylinders. Must be beer time LOL.

Don't know why the images uploaded twice, it's just one of those nights LOL.

So, I’m trying to track down the cause of misfiring/popping on the left cylinder. It happens at all rpms from 1,500 –3,000+ rpm on deceleration/closing the throttle. So far I’ve tried increasing the mixture which had little or no effect. Next I investigated the timing and thought I’d found...

Hi Jabar6, funny you should ask that, it was first registered stateside in 1979 though looking through 650Skull's charts on here the engine/frame numbers say its a 1978 XS-2F (Code 3N0 - whatever that means!). Kinda makes sense as it was first registered Feb 1979, must have had a long voyage LOL ;)

Possibly thinking of the Triumph Hurricane X75? https://www.oldbikemag.com.au/triumph-x-75-short-lived-hurricane/

Hi folks, I’ve been lurking on the site for some time and, after taking delivery of my new (to me) ’79 XS650 Special last weekend, I have now become a member. I purchased my bike from a UK Royal Enfield dealership who had taken it in as a part ex from a customer. The bike has been (mostly)...