71 XS1B Timing nightmare

[pracer]

Without a doubt I am so tired for running around in circles trying to set the timing on this bike. Long story short, bought bike , not running, tore it apart 5 years ago and due to real bad health just putting it back together now. This is what I have, bike is all together, motor was not torn down as it was low mileage. New points and condenser, coils tested 100 %, new battery, all new wiring. I downloaded the way too set the points and then adjust to the timing mark, BUT, no matter what I do the bike is a bitch to start and for a 61 year old body it doesn't take long to takes its toll. When it does run, I check timing on both cylinders to find the rotor mark way over retarded. If I adjust the point plate clockwise to its max movement it starts to bring my timing to Top dead Center, but still falls way too retarded. Am I doing the points wrong ? I have tried from .010 to .016 and got the same issue as far as I can tell, but my frustration is getting the better of me. I am living on a very small disability pension, so taking it to a dealer is out of the question and they probably wouldn't know anything about the bike anyways. I worked at a bike dealer and if the bike wasn't brand new, they had no idea on what to do ! HELP PLEASE, I need guidance before I bugger something up. Any help would be greatly appreciated by this lifetime Yammy rider.

[grizld1]

Welcome, pracer!

Retard position timing should be approximately 15* before TDC (plus or minus a couple), and the factory advance mark falls at 40* BTDC (although many of us find that setting the advance timing to 37 or 38 is preferable). But I think you're saying (correct me if I'm wrong) that when you set the advance timing correctly, you find that the retard timing mark is too far retarded.

If that's the case, the culprit is the advance timing unit under the right side chrome cover. The tips of the bob weights wear where they contact the slots in the disc that controls the ignition rod, and the result is that the advance interval stretches due to the slop; if you dial in the idle marks correctly, the spark will advance into the piston holing range when rpm's pick up, and if you dial in the advance timing correctly you'll be far enough retarded at idle to result in hard starting and startup backfires that will blow the carbies out of the boots now and then.

Don't try to fix the condition by bending or beating the tabs on the ATU rotor to limit bob weight travel, no matter what the shade tree experts suggest; the material is very brittle, and no matter how careful you are, you'll start small fractures and vibration will do the rest. If you want to keep points ignition, one cure is to braze a thin layer of material on the bob weights where they contact the tabs to limit travel, and work it down with a fine file until you get the curve where it needs to be. A better solution is to replace the timing unit (the weights are not and have never been sold separately). Avoid cheap Chinese repops from Mike's XS, etc. Shop around for the Yamaha part; a batch of them was produced a few years ago. The best solution, in my opinion, is to install an aftermarket ignition with electronic advance and get rid of the ATU. Check Probe Engineering (my favorite), Pamco, and Boyer-Bransden.

[madmax]

Are you trying to time at static position (13-17 BTDC) or at full advance (40 BTDC)? For setting at full advance I wedge little slips of cardboard into the advance mech to hold the fingers in the fully open position.

First thing to remember, only ever rotate the engine anti-clockwise when viewed from the rotor side, rotating clockwise can introduce error due to camchain slack takeup being in the wrong place.

One thought, has anyone been into the engine before you purchased? If you can't get anywhere close even at static position then consider that a previous monkey has been in there and somehow got the valve timing out by a tooth? IIRC the XS1 has a 34 tooth cam sprocket(?), this equates to 10.58(ish) degrees of rotation per camshaft tooth and you say the closest you can get is more or less straight up at TDC? Allow a few degrees for the range of adjustment on the points plate and you see where I'm coming from?

You can easily check valve timing by setting the rotor at the "T" mark and then removing the advance/retard mech, the drive pin in the camshaft should be pointing either exactly vertically upwards or downwards depending on which cylinder is on compression.

Worth considering?

Max

[pracer]

Thank you for the responses, greatly appreciated. I was attempting to set timing at idle and found the mark was always over retarded. I looked into the cam chain timing, and it looks ok. Changed the points again just to rule out crap parts, issue stayed the same. Went to the timing advance unit and it looks like hell ( something I totally missed in checking). So I will attack that unit and see what happens. I wish this was happening on my 72, it would be a hell of a lot nicer that kicking the hell out of body ! Will report when something happens, either good or bad. Again, thank you for the help !

[grizld1]

When you say the ATU "looks like hell," it makes me think of the slot that aligns with a pin in the camshaft to hold the ATU in place while the cogged nut is tightened. If the cogged nut loosens the slot will slam against the pin and deform or even break. And yeah, if that nut was loose and the ATU was wallowing around, it would be impossible to get the ignition timing to hold.