Advance Range - Am i missing something

[wherearewe]

Hi guys

Sorry for lengthy post.

Hoping someone can clear something up for me. Ive been trying to get the advance range correct.
In order to not go hard up to or past the full advance mark when setting timing, i have to set the idle timing hard to right side of 'F' range. I did plenty of reading and serviced my ATU and this was no better. It flys out smoothly and snaps back crisply, so the springs work fine.
To experiment with reducing advance range i began peening a 2nd set of second hand bob weights but this just doesnt make any difference. I continually peened, installed, tested and so forth right up to the point that the weights will not touch the stops & barely open. On Pamco Petes Advance video, the bob weights are able to fly out and hit the stops, (it looks like at least). The fact that I made no difference makes me wonder if i am missing something. I expected a reduced range of movement to change the advance timing.

The bike is an 81. NZ and Australia models shipped with points, so i didnt install the ATU. I did fit a pamco. Below shows the mark where i have to time it too at idle and still go hard up to full advance. There is a little video too to show how limited the bob weight range is (mediafire link since i dont have a youtube account).

Am i being a total egg? I found this thread which made me think I was on the right track.

What is the ideal point to aim for? I read somewhere 1/4 inch before the full advance mark.

Thanks very much

http://www.xs650.com/forum/showthread.php?t=10696



http://www.mediafire.com/?49q5dzk3jlxvdag

 

[pamcopete]

wherearewe,

Having your advance "snap back" is only part of the story. If your springs are too loose, then some of the advance is used at idle leaving not enough to go to full advance. If your springs are too tight, the full advance will occur at a higher RPM than 3,000. So, you have to play with the springs to get the advance to occur at 3,000 RPM.

 

[gggGary]

OK here is my simple "too much advance" fix.
I did this on my 79 with 20K miles and a pamco, it had "excessive advance" about 5 degrees too much, have put 6-700 miles on it but need to recheck timing and confirm the weights have stayed in place. So if you do this you are part of the testing program....
The advance weights swing out and contact the inside of the rotating housing. I just glued some shims made of pop can to the inside of the housing, reducing how far the weights can swing, done. The thicker the "shim" the less they can "advance".





Even with a blow up they are hard to see, I used some high temp silicone to hold them in place.

the springs were shortened a bit, I got lucky and found the circlips when they went flying (twice!)

I might be tempted to tap holes in the stops and use set screws as an adjustable advance limiter. Discussion welcome.

 

[pamcopete]

gggGary,

I did something similar once on my '78/R using heat shrink tubing on just one of the tabs. This holds one of the weights steady before the other. The result is that the weights grip the slotted disk and prevent it from flopping around.

 

[weekendrider]

To experiment with reducing advance range i began peening a 2nd set of second hand bob weights but this just doesnt make any difference. I continually peened, installed, tested and so forth right up to the point that the weights will not touch the stops & barely open

At this point, where the weights wouldn't touch the tabs, it still advanced too far?
Shimming the tabs wouldn't work. If it isn't touching it isn't touching regardless of the reason.

 

[gggGary]

At this point, where the weights wouldn't touch the tabs, it still advanced too far?
Shimming the tabs wouldn't work. If it isn't touching it isn't touching regardless of the reason.

The good news is he did the peening to an "extra" set of weights. The weights do hit the stops as designed so with an unpeened set of weights the "shims" should function to reduce the total advance available, they did for me. After a rough timing set static the rest of my timing is done with a timing light.
It would be awesome if Pete could whip up an electronic ignition with advance so we could toss the wobbly inaccurate mechanical advance completely.

 

[weekendrider]

gggGary you are missing my point and the OP isn't back yet.
He stated he peened them till they would not hit the stops and still had the problem.
Sooo....again if it isn't hitting it doesn't matter why it isn't hitting, shim or peening, it isn't hitting, but still advances too much. Seems to me that would take the position of the weights out of the picture. Maybe I misunderstood, the OP will be back I'm sure.
I had good luck peening, paying attention to measurements and filing to smooth.
I can say with all honesty the 79F is still stock with the originals.
Close to 20K now. Still have all the bits and pieces it came with.
NO adjustment left on the drive chain, a bald rear, only 7 threads left on the cam chain adjuster and the points plate all the way to the left I've gotten about all the goodie out of some of these parts.

 

[gggGary]

Weekendrider your point is taken. I sometimes try to be subtle, wink.
A timing light is needed for accurate timing, it shows when the advance takes place and highlights any misses or wobbles in the timing. Not sure how the OP has been checking his advance...

My pics are also of a 20K 79 now with pamco. After some rather frustrating messing with setting, timing the stock points, I put on the pamco, while doing that I found what was probably my original problem, a malformed, loose spade connector on one of the coils.
I admit to not having done a peen the weights mod. I haven't said it before now but I thought there might be a different way to limit advance. Shimming the stop will reduce advance. How much shim is needed needs to be determined on each bike. The weights may be worn and need replacing also. The pivot holes should be checked for wobble. Springs are always "needs checking" items, points wear out also. Lots of variables, hard to separate them all. I was just mentioning a method that helped me reduce the total advance.

Ok went and reread the OP, cam chain slop can affect total advance also?

 

[resto]

I would like to chime in on what I find as a fascinating subject with some of my observations and "humble" opinions.

This summer I finally got around (mainly because xs650direct had them in stock) to installing a Pamco ignition package (Part #14-0901).

Prior to this this, when checking my timing with a good timing light (and cam chain properly adjusted) I found that the strobe mark danced around a bit at all RPMs, full advance timing was too great even when the idle "F" mark timing was correct, and sometimes the advance took its sweet time to go back to "no advance" at idle. The last observation I am sure is what caused my idle speed to sometimes stay higher than it should. Like member wherearewe, I too compensated for having too much advance timing by retarding the idle timing to the right of the "F" range. Seemed like the lesser of two evils, I don't like to hear pinging and retarding the initial timing made it easier to kick start the bike anyways.

Before removing any of the point ignition system, I tried the snap test and found that it really didn't "snap" all that well depending upon where the slotted disk was in its static state. I figured this had to do with the fact that in some of the snap tests, the ignition cam lobe was rubbing on points arm, and sometimes it wasn't.

First to come off was the points plate. I redid the snap test. It was much better now, but still not consistent. I could feel that the advance shaft was binding slightly in the head so I removed it, greased it, and the snap test was 100% now.

BTW, I would recommend for anyone with inconsistent idle speeds to grease the shaft, it could solve your problem.

I put on the Pamco unit and coil and set the initial timing. Right from the get go I noticed that the timing light strobe was rock steady but I still had too much full advance timing, so again has to retard the initial "F mark" timing to compensate.

Noticed a huge seat of the pants performance gain on my first drive but also noticed that if I gave it full throttle at 2000-2500 RPM, I could get it to ping slightly. It never did that before. Granted, I do have over 25,000 miles on the clock so the motor is probably looser than most.

I intend to use Pamco Pete's or gggGary's method of limiting full advance by making sure the bob weights actually have something to limit their movement at 3K RPM. Once that is done, I can properly set the intial "F" timing where it should be instead of it's compensated setting. I was awfully tempted to bend the tabs though.

My next observation, and I would like to hear your opinions on this, is that with the points gone, there is now almost no rotational load for the bob weights to work against except off course for the load imposed by the advance springs. In my mind, the weights now have an easier job since they don't have to work against the force needed to open the spring loaded points setup.

I think that because of that, the timing is advancing too quickly and that is why I am noticing some under load pinging between idle and full advance at 3K. Stiffer springs (or lightly bob weights) would probably fix this conditions. There is a possibility that some of the pinging may be caused by virtue of having a fatter spark and therefore better combustion.

It would be nice to have access to the what the original timing curve looked like from the the factory and what it now looks like with no rotational point cam load being in place. I really suspect the timing is advancing too quickly and am going to play around with spring weights for sure. I have already bought a set of springs from xs650direct and will experiment with them.

Wished that before I took out my point ignition that I would have checked to see how much advance I had at, say, 2000 RPM and compare it to what I have now. Maybe someone who is about to go through the ignition upgrade could do that and get back to us.

Just my $0.03


resto

 

[gggGary]

Good slow methodical detective work there Resto. I think mine was advancing too early even before the Pamco. On springs I clip off one end and bend in a new "hook" if that sets the advance too late I stretch them a "little bit" till the advance is in the correct RPM range, the one I did now finishes advance at a bit above 3000 and I have no ping. It only rattles if I lug it really hard at very low RPM off the line. I am impressed the engine will pull down that low but avoid it.
My dad was notorious for driving a clutch that way in the pick up, I would cringe every time he made those rods (pistons maybe?) rattle.

 

[retiredgentleman]

The spring tension is very important, and the OEM springs work the best. I tried using the ATU springs from xs650direct, and did not like them. I was getting a flat spot in acceleration, folowed by a guick burst of acceleration as the weights flew out. I went back to using the OEM springs, and still use them as they give a linear acceleration.

I have had good results with the peening method to limit the advance. However, I have found that the advance range widens out each year if I don't re-peen the fly weights. So once a year, I check for the fit in the slotted disk, and have to do a minor re-peen to get a tight fit in the slots of the slotted disk.

Interesting ideas to glue a shim or use some heat shrink tubing to limit the advance. I have also thought about drilling and tapping to use a small adjustable screw.................maybe I will experiment with that idea this winter.

Lets face it, the mechanical advance is a crude device but it does get the job done. An electronic advance would drag us all into the 21 century.

 

[pamcopete]

resto,

If your timing is right at the edge of pinging, then use higher octane gas. The buildup of carbon in older engines increases the compression ratio slightly as well. Also, with the much hotter spark with an electronic ignition, more of the mixture is ignited leaving less to act as a coolant, so you could also try a slightly richer jet configuration. It's kind of a paradox with a hotter spark that at a steady throttle position you will burn less gas because of the increased efficiency, but during acceleration because more of the mixture is ignited it's almost like running lean, so you can actually use a larger jet and get more power and better gas mileage!

(Cake and eat it too, kinda thing... )

 

[wherearewe]

Interesting thread here!

WeekendRider is right "Sooo....again if it isn't hitting it doesn't matter why it isn't hitting, shim or peening, it isn't hitting, but still advances too much. Seems to me that would take the position of the weights out of the picture. Maybe I misunderstood, the OP will be back I'm sure."

This is what is confusing me. I was able to peen the tangs of the bob weights to the point that they would only open perhaps 3/4 of their range. The action was smooth but simply limited. I could see the slotted disc was only turning maybe 8 degrees? There is no way centrifugal force was opening them fully.
This gives the same end result as gggGary's shim experiment - limited weight opening. I expected this would reduce the advance range - I didnt really care about how much, it was an experiment.
I grabbed my timing light and fired away - But the range doesnt change. Static timing was the same as i expected. Under throttle I figured it would only move a few inches, but no, it slides right out to hard up to the maximum advance indicator as though i had changed nothing.

I wonder if you could shorten the advance range the opposite way. Put some jb weld on the inside of the weights so they stay slightly open, therefore the timing at idle is advanced a few degrees. Then adjust the overall timing so at full advance its where you want it.

At the end of the day though, that doesnt explain to me whats going on. A new ATU is 220 US inc shipping (290 US through us through my local yamaha dealer). Sounds reasonable.
I dont know about Mikes ones. The other tread I found that was relevant, the Mikes unit didnt solve the problem. Heatshrink did.

I really don't feel like buying a new ATU unless i can work out whats at fault.

 

[wherearewe]

Also there is a lot of talk about the springs. My understanding is this -

The springs control the RATE of advance. Nothing to do with RANGE really (unless they were waaaaaaaaay wrong).
The slotted disc is what determines range, and that is controlled by the bob weights.

Correct?

 

[pamcopete]

Well, again. If the springs are loose some of the available advance movement will be used up at idle. If the springs are too tight then full advance will occur past 3,000 RPM, like maybe at 10,000 RPM. In both cases, too tight or too loose, the range is less than it would be with ideal spring tension.

To get a picture of this, imagine what would happen with no springs and what would happen with wire in place of the springs. In both cases you would have zero advance from idle.

 

[wherearewe]

Well, again. If the springs are loose some of the available advance movement will be used up at idle. If the springs are too tight then full advance will occur past 3,000 RPM, like maybe at 10,000 RPM. In both cases, too tight or too loose, the range is less than it would be with ideal spring tension.

To get a picture of this, imagine what would happen with no springs and what would happen with wire in place of the springs. In both cases you would have zero advance from idle.

Ok i see. So bad springs equal potentially LESS range. Anyone got some bad springs i can put on!

But in a situation like mine where the range is too much, i would imagine we can take springs out the picture? I do actually have 3 sets of springs. 2 used OEM, 1 mikes unused. I could swap the springs and report back?

 

[resto]

Also there is a lot of talk about the springs. My understanding is this -

The springs control the RATE of advance. Nothing to do with RANGE really (unless they were waaaaaaaaay wrong).
The slotted disc is what determines range, and that is controlled by the bob weights.

Correct?

Correct, springs and/or the mass of the spinning bob weights control your rate of advance. Still, you do not want to go beyond the full advance mark so I see no harm in limiting the travel of the bob weights so they can't swing out any further at 3K rpm.

Lots of good info in the responses from gggGary, Pamco Pete, and retiredgent. That's what this forum is for, to pool our knowledge.

For you visual people, I have included a graph I stole off the Internet from Car Craft magazine. It shows the timing advance curve from one of their engines on a dynometer. Notice the linear rate of advance from idle to 2400 rpm where it tops out at 35 degrees advance. Also note that even though the engine revs to past 6K, the maximum advance still stays at 35 degrees.

This is my ammo for hard limiting the total advance on an xs650 by some sort of mechanical stop, be it shims or other method.

Pete, I considered your suggestion (and will use it in the short term) of running premium gas to keep the pinging at bay, but with a stock compression ratio of 8.7:1, it shouldn't be necessary. You are probably right about the carbon buildup and I am running 17/32 sprockets. But in my defense, I only weight a buck sixty five. I think I will play with the advance springs so more instead of paying a premium (hmm, maybe that's why they call it that) at the pump every time I fill up. For now, if I need hard acceleration in the 2500 rpm range, I kick it down a gear.

I'm glad wherearewe started this thread. It's a great topic.

 

[weekendrider]

Would the position of the gear on the cam make any difference?

 

[wherearewe]

Update. I spent some time this morning messing around. Put back my original weights. It didnt seem to matter what i did with springs, although i was able to change the rate of advance, i couldnt seem to reduce the range. So for example, i could make it hit the full advance mark at 5k or 2500k and hang.
Then i noticed something. When one weight was opened fully, the other weight had a little travel (SEE PIC) If i pushed it out the last mm, the cam was able to turn a little more. Close inspection revealed some dings. Perhaps a PO had whacked it. I wonder if the stop has been bent out slightly. Combine that with a some wear to the weights and and disc they slot into, and maybe that is causing excess advance movement. I am going to test by blobbing a little JB weld onto the outside of one of my 'test' weights so it hits the stop.

At the end of the day though, it still doesnt explain how, even when i heavily restricted the weights from opening by peening the crap out of them (so they couldnt contact the stops) the advance range wasnt changing. I could have underestimated the centrifugal forces I suppose. I might try a test tomorrow with some heatshrink and some lead tape or something - to attach them to the stops temporarily to see what effect that has.

 

[pamcopete]

Well, here is where the mystery comes into the scene. People will pay $500 to $700 dollars to paint their gas tank. They will tear down their engine and spend another $600 putting it back together because it had a minor oil leak, but when the advancer has gasped its last breath after 35 or 40 years, they will not spend $65 for a new advancer. Instead they peen the weights, cut the springs and screw with it for two weeks instead of just buying a new one.