timing troubles and identification help

[kawabunga]

Hello, new to the forum here. I picked up a '79 XS650 basket case. First off, I'd like to determine exactly which sub-model of XS I have. Engine number is 2F0-173457, according to the tables I found by googling "XS650 identification", I should have an XS-F. Does that sound correct?

My main reason for posting is that I'm having trouble getting the static ignition timing set. I'm following the procedure outlined in the Clymer manual for 1970-1982 650 twins. No matter what I try I am not able to set it to where my test light just comes on at the firing mark on the flywheel.

The bike is a mess, it was not running when I got it and the guy I acquired it from never had it running himself, but supposedly the previous guy did. So, I have no history of the machine and it has been hacked into already.

I got it running, it will idle, but it pops and spits a lot while doing so. It doesn't like getting throttle either. I checked/adjusted the valves, intake in the .0025-.003" range and exhaust at .006". New points set to .014", new condensers and new plugs. It has good spark and the carbs are clean. I disassembled and reassembled the auto advance unit and pulled the rod in the cam going to the points cam and attempted rotating it 180 degrees to see if that made a difference, but had no luck.

What am I missing? Is there something could be flipped 180 degrees that would make it impossible to set the static timing? Could the valve timing be off? It currently runs, not well but it does, so I'm not too suspicious of that. I attempted to find thorough instructions for installing the auto advance unit but was unable to, and the manual isn't too clear. Does anyone have a link or know-how on the proper way to install that?

Here's some photos of how it's currently set up. Does anything stand out as wrong?

Thank you in advance for any advice .
kawabunga

 

[gggGary]

You don't mention setting cam chain tension. Idling til the rod quits moving back off about 1/3 turn. There's detailed threads. Have you cleaned the oil screens? Anything of note in them?

 

[kawabunga]

You don't mention setting cam chain tension. Idling til the rod quits moving back off about 1/3 turn. There's detailed threads. Have you cleaned the oil screens? Anything of note in them?

My mistake, I did adjust the cam chain tension, but not while running. My manual did not state to do so. On that topic though, I was a little confused about the adjustment process. (I'm used to Honda CB engines). When adjusting the cam chain tension, is the plunger supposed to move in and out at all when you're done adjusting? Or is it not supposed to move at all? Right now mine moves a couple millimeters at most. And when it is moving, do you set it flush when it's at its furthest point out or furthest in?

I have not investigated any oil screens yet. What should I be looking for? I'm assuming ideally I shouldn't find anything in them...

 

[5twins]

The only possible error I see in your pics is the notched ring that holds the advance unit on. It has a raised ring or lip around it's I.D. on one side and that should face out. If it isn't, the ring can't be tightened down properly and won't stay tight. I don't see the ring in your pic .....

The cam chain adjustment while running is something we came up with so you won't find it in a manual, at least not a 650 manual. I did actually borrow it from the adjustment procedure for another model, the SR500. It's not the actual setting procedure but rather a check you run after setting it with the motor off. You want to observe a slight amount of in-out movement on the rod, maybe a MM or 2. If there's no movement, you've set it too tight. But, it turns out to be an easy method for doing the adjustment too, easier, I think, than the manual procedure. I think the fact that the manual procedure has you totally confused proves my point, lol.

You say you can't get the timing exact. How far off is it? How many miles are on the bike? If it's high mileage and the cam chain is all stretched out, that can cause you to run out of adjustment slot on the timing plate before the timing is correct.

 

[kawabunga]

I think the notched ring you're talking about is there. Does this pic show it better?

18,700 miles on the odometer. I rechecked the cam chain tension based off an article I found here. I'm fairly certain I've got it set correctly. The pin moves about 1-2mm. But, no matter how much I tighten the adjuster it will not come to exactly flush with the end. It's close, but not quite, and if I tighten it anymore the rod stops moving in and out. So I set it where it had a little movement yet.

And here's what I've got for adjustment.

In this image the points plate is rotated all the way to the stops clockwise.

I placed a wrench on the advance rod to show placement of the cam. I've taken up the "slack" in the wrench but have not rotated the rod yet.

If I rotate the advance rod counterclockwise with the wrench, the test light comes on. I'm not turning it very much.

Hard to tell in the photos so I overlaid them to help illustrate.

Here's where the flywheel is at, right cylinder TDC.

And lastly, here's a video of it running from tonight. It'll idle on its own but pop and backfire a lot. Will accept a little throttle but I didn't give it much given the state of things.

 

[gggGary]

Perhaps worth mention; there are two ways to set up a static timing light, one way has the light come ON at opening the other has it go OFF. One lead is on the points wire, the other can go either to ground or to +12 (hot). adjust points plate to where the bike seems to idle and rev well, then check timing with a strobe (gun) light if the light has an advance dial be sure it's set to 0 degrees.

 

[5twins]

The fact that rotating your cam slightly triggers the test light is showing that the timing is close, you just don't have quite enough adjustment left on the points plate to get there. I hope you know you shouldn't be trying to turn the motor over with that little nut on the cam. Use the big nut down on the crank/alternator for that. You could try closing your points gaps up to .012". That may give you the little bit more adjustment range you need.

Also, your lower points set gap (left cylinder) looks too big. I can see it in the pics and in the video. If you watch the video, note how much more that lower points set moves as it's opening and closing compared to the top set. That could be causing the popping and misfiring. It's also possible you contaminated the faces of the points with oil on the feeler gauge blade you used to set them. That could also cause misfires. Clean the points faces. The usual method is to cut 1/4" strips from a plain white business or file card, spray with electrical cleaner, and drag it through the points like a feeler gauge. You will need to relieve some pressure on the points as the card strip won't pull through with them clamped down tight on it, it'll just tear. Lift them open slightly so the card strip pulls through with a slight resistance.

Also note that the idle timing doesn't have to be exactly on that "F" mark, it can be anywhere in the 4° "range" indicated by the 2 smaller slash marks on either side of the "F".

 

[kawabunga]

Thanks for the recommendations, 5twins. I'll try those suggestions out when I get back from out of town.

On your note about rotating the engine from the advance rod nut, absolutely not. I was only turning that to illustrate how much further the cam love had to turn. I only turn the engine over via the flywheel nut or the kickstarter.

 

[kawabunga]

Back home now, had a chance to do some testing.

I readjusted the points gap to .012" and cleaned the contacts. I then rechecked the timing and still am right up against the stop on the timing plate. I tried it at either end of the timing window that you pointed out on the flywheel, 5twins. No dice on either end. Again, if I take a wrench and turn the auto advance rod the light will come on.

I think closing up the points gap helped marginally, which makes sense if the timing is too retarded, but it's still too far out. It was intermittently better, and I think I figured out why. I noticed that after I ran it for a while that the cam the points ride on was making some squeaking noise. I lubed it very lightly with some electric grease. The squeaking went away and the advance rod then turned much more freely on the points, so I think it was sticking and making the auto advance go whompy.

This got me thinking, so I did a little experiment that yielded some solid results.
First, here's how the bike runs after setting the points to .012" and cleaning the contacts. The idle has to be turned up very high, nearly to the stop, but it will idle. It spits and pops - sometimes a lot, sometimes not as much - but always does it. It also does not want to accept throttle. Sometimes the revs will pick up slightly but it sounds like it's loading up really bad and just shuts down. If it does rev up, it spits and pops much worse.

Since the timing light came on when I advance the timing manually via the auto advance rod, I thought I might as well see what it does if I force the unit to advance the timing from the get-go, rather than at a higher rpm. I did this by inserting some folded up card stock between the weights and the rod end.

With the advance unit forced open, the bike fired right up, idled much smoother and accepted throttle readily. I was also able to turn the idle down a lot from where I had to have it without the timing advanced. It almost runs great with the paper wedged in there. It's still a little off, you can hear some popping, but it's clearly much better than without the advance unit fully advanced...or near fully advanced, I didn't stuff like the Thanksgiving turkey.

So, my timing is too retarded, correct? What are potential causes? Could the timing chain be off a tooth? Could my timing chain be stretched at 18,000ish miles? Other ideas?

 

[TwoManyXS1Bs]

Closing the points gap will retard timing. Set them back up to 0.016", and reset ign timing.

You can get a fair idea of chain stretch. Remove plugs, slowly rotate engine back/forth around the TDC mark. One cylinder's valves will be on overlap (exh closing, intake opening), and they'll try to push the cam to get equal pressure, and the crank wants to settle somewhere past TDC. Once you find this "equalized" position, compare the "T" mark to the rotor mark.

Mine has a stretched camchain, and shows a bit over 10° retarded, as shown by the rotor mark rotated past the "T" mark.

Just an FYI, I run my points with a larger gap, about 0.020". This allows me to put the points plate at just before its full advance position. But, don't do what I do, unless you're comfortable with it...

 

[grizld1]

1 tooth=10* of camshaft rotation=20* of crankshaft rotation. So no, that isn't your problem. Re. the cam chain, durability depends on prior maintenance. I've seen them go 50K miles and I've seen them worn out at 15K.

 

[gggGary]

Have you removed checked cleaned the advance rod? while doing that make sure the advance rod locating pins on both ends are in place......... It's possible bubba lost one and the two slot advance disk is just clamped to the advance rod by the nut.

 

[5twins]

There is also a locating pin in the cam that locks the advance unit on in the proper spot. The weights on the advance unit hook into the disc on the advance rod and properly position it and the points cam on it's other end - if all the locating pins are there. So there are a total of 3 pins, one on each end of the advance rod and one in the cam behind the advance unit.

As Gary mentioned, the advance rod must be clean and well lubed so it easily rotates back and forth through it's range of motion. This is what advances and retards your timing as the RPMs go up and down. Yours might be sticking or hanging up just slightly advanced, not quite fully retarded. Seems you can make it go that little bit more to full retard with a wrench.

When I static time I don't place the rotor mark on the "F" and then move the timing plate all around until the test light comes on. Instead, I start with the rotor mark an inch or so to the left of the "F" mark, over by the full advance slash mark, hook up the test light, turn the key on, then slowly rotate the crank until the light just comes on. If it comes on before reaching the "F" range, this tells me the timing is too advanced, firing early. If it comes on after I get past the "F" range, this tells me the timing is firing late or too retarded. Knowing exactly where it's firing tells me which way I need to move the timing plate.

 

[kawabunga]

Closing the points gap will retard timing. Set them back up to 0.016", and reset ign timing.

My mistake, timing in regards to advance vs retard confuses me easily.

You can get a fair idea of chain stretch. Remove plugs, slowly rotate engine back/forth around the TDC mark. One cylinder's valves will be on overlap (exh closing, intake opening), and they'll try to push the cam to get equal pressure, and the crank wants to settle somewhere past TDC. Once you find this "equalized" position, compare the "T" mark to the rotor mark.

Just an FYI, I run my points with a larger gap, about 0.020". This allows me to put the points plate at just before its full advance position. But, don't do what I do, unless you're comfortable with it...

I will try that and see what I find.

1 tooth=10* of camshaft rotation=20* of crankshaft rotation. So no, that isn't your problem. Re. the cam chain, durability depends on prior maintenance. I've seen them go 50K miles and I've seen them worn out at 15K.

Good to know, thanks.

Have you removed checked cleaned the advance rod? while doing that make sure the advance rod locating pins on both ends are in place......... It's possible bubba lost one and the two slot advance disk is just clamped to the advance rod by the nut.

I have removed the rod, but only by removing the points cam. Now I'm curious about the advance side. I'll look into it and report back.

There is also a locating pin in the cam that locks the advance unit on in the proper spot. The weights on the advance unit hook into the disc on the advance rod and properly position it and the points cam on it's other end - if all the locating pins are there. So there are a total of 3 pins, one on each end of the advance rod and one in the cam behind the advance unit.

As Gary mentioned, the advance rod must be clean and well lubed so it easily rotates back and forth through it's range of motion. This is what advances and retards your timing as the RPMs go up and down. Yours might be sticking or hanging up just slightly advanced, not quite fully retarded. Seems you can make it go that little bit more to full retard with a wrench.

When I static time I don't place the rotor mark on the "F" and then move the timing plate all around until the test light comes on. Instead, I start with the rotor mark an inch or so to the left of the "F" mark, over by the full advance slash mark, hook up the test light, turn the key on, then slowly rotate the crank until the light just comes on. If it comes on before reaching the "F" range, this tells me the timing is too advanced, firing early. If it comes on after I get past the "F" range, this tells me the timing is firing late or too retarded. Knowing exactly where it's firing tells me which way I need to move the timing plate.

I get what you're doing there. But what if I'm out of room for adjustment? I am completely up to the stop on the points plate, I've even removed the screws that hold it in place and rotated it further and that's still not quite far enough. It's close, but not doing it. Maybe there's something off about the advance rod that I've missed so far...

 

[5twins]

Check to see that all 3 locating pins are present. That's about the only thing that would throw the timing off other than a stretched timing chain. You can assemble the advance rod incorrectly, have the locating pins 180° off from one another, but that then throws the timing off 180°. You're not off that far. My chain was about toast at 22K when I replaced it. I could still time it but I was practically out of adjustment slot on the timing plate.

The cam chain tensioner is a spring-loaded rod that pushes a rubber "shoe" against the back side or run of the chain. As it eliminates the chain slack, it rolls the cam backwards slightly. That retards the timing. You compensate for it by adjusting the timing plate but eventually, once the chain stretches too much, you can't do it anymore.

I see by the red gasket sealer on the top cover joint that someone has been into that topend before. Yamaha used their Yamabond on that seam, which is gray. Maybe they did assemble the cam with the timing chain one tooth off. To check for that without tearing too much apart, remove the advance unit, set the motor at TDC (on the "T" mark), and observe the location of the pin hole in the cam. It should point straight up or straight down.

 

[kawabunga]

I disassembled the auto advance unit and rod completely tonight. Everything checks out in my eyes based off what everyone has mentioned. Have a look.

Pins are facing the same direction.

I didn't move the rod between these two photos, just went to either end for the photo.

Cam and disk front and back look good.

Aside from one of the tiny washers missing, all looks well on the advance unit as well.

And pin is in place on the cam.

With everything apart, I then set the engine at TDC with the T mark on the flywheel to check the position of the pin for the advance unit on the cam.

And the other side. (Not sure what I was doing here, I thought I had it set at the T mark when I took the photo... Not ideal but it's close and the other one is on the money so I thought I'd include it anyway.)

And that looks off to me... I'm assuming the pin should be straight up and down in relation to the top of the three screws behind the advance plate?

With everything checked over, I cleaned, lubed and reassembled everything.

I then set the points gap to .020" like TwoManyXS1Bs had mentioned. It got the timing a bit closer but still not there. The bike actually ran a touch better than with the gap set at .012" or .014". I still had to have the idle set high and it was still popping and sputtering, and still didn't like throttle. So I tried the paper in the advance weights thing again and it made a tremendous difference. Like the last time, it still had some popping here and there but very minor compared to without the paper in the weights, but it idled much smoother and accepted throttle with ease.

One other thing I noticed while doing all this, and maybe should have noted before but I didn't know it was an indicator of anything, was that it's very difficult to the get the engine to sit at TDC, with the T mark on the flywheel lined up. It really wants to swing past the mark on every rotation.

Here is where the crank wants to come to rest when trying to get the engine to sit at TDC.

Each rotation has maybe a couple of degrees in variance from this position, but in general, this is where the crank naturally comes to rest when turing it. I have to be very careful about rotating the crank when trying to set it at TDC otherwise it just wants to swing right past it, just like TwoManyXS1Bs had mentioned.

Based off what I found, and compared to what you guys have mentioned, would you say it's looking like a worn cam chain?
Could it be a faulty cam chain tensioner?
If it is time to replace the cam chain, should the tensioner, or any of its components, be replaced at the same time?
And can the cam chain be replaced with the engine in the bike? In general, how difficult is it?

Also, I wanted to say thank you for all the help thus far! You all have been a big help and I really appreciate it.

 

[5twins]

It looks like your advance rod has been running dry for some time. See those grooves on the bushing I.D. in the end of the cam? They should be kept packed with grease to keep the advance rod lubed .....

Your cam timing may be off. The cam may have been installed with the chain one tooth off on the sprocket. There is a notch on the cam sprocket. You place the motor at TDC, point the notch straight up, then put the chain on. The P.O. may have thought he had the notch pointing straight up but I'm thinking he didn't then set the cam chain tensioner. Remember, that rolls the cam backwards a little.

 

[TwoManyXS1Bs]

Looks like you're running about 10°-15° retarded. It would take 20° to be off by one tooth. Stretched camchain...

 

[kawabunga]

Either way it looks like I'm taking the cam cover off. I can verify cam timing at that point.

Do you guys have any recommendations for a replacement cam chain?
I'm going to have to go with a linked one rather than endless since I'm not going to split the case at this time.

Also, should I do anything with the cam chain tensioner while I'm in there?

 

[kawabunga]

After doing some searching, I see that you have to pull the head in order to replace the cam chain tensioner/guide. With 18,000 miles on the bike, do any of you see this as a necessity at this point?
Is it worth it to replace the tensioner spring? At least I can get to that without pulling much apart.
Or is all that just unnecessary extra? Just replace the cam chain and move on... I don't really want to do more than I need to at this point but I also have the, "since I'm in there..." thought running in my head. That's a dangerous phrase.