Totally stumped

[kzcafeace]

OK here it goes. I have a 1983 xs650. I've been riding for many weeks. It would die only once an a while like at the occasional stop light, no big deal it would just fire right back up and off I'd go. Unfortunately lately it dies almost immediately after hitting the road. and when i try to restart it it pretty much won't. I hear it firing while I'm cranking the starter but it won't hold its idle. But here's the confusing part it will hold a great idle when first started and runs like a raped ape when I run the bike down the road at full throttle but it will die when cruising. Remember none of this was a problem until about two weeks ago. Something has changed and I can't figure out for the life of me whats going on. I've checked the mechanical timing, good.
I've checked the valve lash, good. Checked dynamic timing. I have the PAMCO ignition, new coils and new mechanical advance so the springs are good. the fuse panel is new. The jetting on the carbs has never been an issue, not too rich, plugs look good and had lots of power. But lately it dies NOT like its running out of fuel and NOT complete instant electrical failure. lights all stay on. its like it losses ignition abruptly for no good reason. I even swapped out carbs it didn't help so I swapped it back. Virtually if you can think of it or replaced it I've done it or so I think. I am sooo stumped as to why its suddenly dies and then becomes so hard to restart only to die again moments later. I have a burning question though how susceptible is the PAMCO system too over heating and failing? Any suggestion is appreciated I would really like this bike up and running by wednesday. OH and I even removed the little PCV valve that I had on it for a long while without problems because I thought maybe it was causing a build up of crankcase pressure and locking the engine up. It almost felt something exactly like that but removing the PCV valve solved nothing.

[pamcopete]

kzcafeace,

Well, I'm not sure what you are trying to show us with the pics, but the timing at idle should be as in your second pic, and the timing at full advance should be as in this pic at 3,000 RPM:



You have to use a timing light to set the timing.

Another thing to look for that could cause your symptoms is if the advance rod is sticking. The advance rod should "snap back" as in this video:



There are several other possible problems that can cause rod sticking, so review the advance installation instructions on the site:

www.yamahaxs650.com

[kzcafeace]

I set the pistons to TDC and the first pic shows exactly where the timing mark on the rotor lined up the the stator. So i'm confident that the mechanical timing is good. The second pic shows where I believe the timing mark is suppose to be at idle. The third pic shows where my actual dymanic timing is at idle with a timing light. When it get it some throttle it advances is the direction that you showed in your picture. Question, When I'm using the timing light the best I can do for timing requires that I have the strobe light slightly advanced 10% on the knob on the timing light. If I put it on 0% it won't quite dial in.

Everything was going pretty well until one night while driving around pretty hard I was heading back cruising in the freeway around 60-70 MPH and then suddenly she cuts out. I couldn't get her restarted at 2am along side the freeway so I just slept in the woods because I know she seems to always start up fine when cold. Sure enough a couple hours later It started up and I made it home. About the mechanical advance rod, I had that problem before. I found out that the weights where sticking hard in the advance position when the engine would heat up and seize the advance rod. So I have already removed, sanded and lubed the rod before. Seeing how this syptom greatly resembled that incident I removed the rod and again sanded down the rod and bushing and lubed everything. I didn't have a problem with the bike for the longest time after the first fix and the second attempt had no positive effect on the bike's condition. The bike idles fine and advances when I crack the throttle even when hot but the weird thing seems to be that it can't handle a load on the system when I'm riding it unless I'm wide open. The mechnaical advance goes on the right side of the engine right? The weirdest thing is that when it does fail it doesn't want to restart. I'm going to really open up the bushings around the advance rod and get back to you.

[xsleo]

It sounds more like a carb problem to me. Maybe both sets of carbs need cleaning.

[pamcopete]

kz....,

Well, the dual output coil produces a positive voltage on one plug wire and a negative on the other. The timing light works best on the negative wire, but there is no easy way to determine which wire that is, so try switching the timing light to the other wire.

I don't like timing lights with a built in degree setting, but if you are going to use one, then it should be set for 15 degrees at idle and the timing would then show up at the "T" mark, or at least that is my understanding of how they work, so I'm not sure what you will get if you set it to "10% ".

There are several causes for a binding advance rod listed in the web site www.yamahaxs650.com in the advance installation section. One of the causes is the pin that holds the advance mechanism being too long and pushing on the inner bushing enough to distort the bushing or cause it to be misaligned with the other bushing. Please read through the section and try the suggested methods to eliminate binding.

[ShakerNorm]

Actually sounds like fuel starvation - as the carbs were getting just enough fuel for a little while - then plugging up and starving the engine.

I had a similar problem on mine, and it turned out to be the fuel tank cap. It couldn't vent and as the fuel got used - the tank developed a slight vacuum - and wouldn't drain any more fuel into the carbs. Cleaning the little vent holes on the fuel tank cap let air back into the tank and cured it!

[czechbiker]

I think Shaker Norm is on the right track. Sounds like a vapor lock to me. I would check petcocks and fuel flow. Sounds just like what happens when I forget to open my manual petcocks after a rest stop and she dies out after riding for a min. or two.

[mrriggs]

Aug 18, 2010 5:52:18 GMT -5 @pamcopete said:

I don't like timing lights with a built in degree setting, but if you are going to use one, then it should be set for 15 degrees at idle and the timing would then show up at the "T" mark, or at least that is my understanding of how they work, so I'm not sure what you will get if you set it to "10% ".

Unless your light has a setting for waste-spark ignitions it is assuming your ignition is firing every 720°. Since your bike is firing every 360° you need to cut the dial reading in half.

Like Pete said, to use one of those lights you use the TDC mark. With the engine running, shine the light on the timing marks then turn the knob until it looks like your first picture. At idle, your knob should be around 30° which would indicate 15° of advance. Since your knob only goes up to 60° you won't be able to read the total advance directly since 60° divided by two is only 30°. The total advance spec for these motors is 40°. The best you could do is rev up the motor and turn the knob until it looks like you second pic then take half of the dial reading and add 15 to find the total. Or just forget about the knob and ball park it like Pete suggested.

[pamcopete]

I put these pre set advance timing lights in the same box as auto ranging multimeters. The makers are trying to do your thinking for you, but they have no idea of your actual circumstances.

In the case of the XS650, you have a wasted spark ignition that screws up the auto timing timing light and a crude mechanical regulator that screws up the auto ranging meter.

It's all part of the new "fun and easy" mentality that is ruining the country and is a major cause of global warming and the infestation of army worms that ruined my front yard.

Note: Virtually all modern cars use a wasted spark ignition system and their plugs fire every 360 degrees, just like the XS650, so If you insist on using a pre set advance timing light, get one for wasted spark systems, which will probably cost 2X what an ordinary timing light costs.