Advance bob weights and springs question?

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Its been a long time

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A bit more progress on the bringing back from the dead XS650D project. It seems this bike (no history) had a number of new parts fitted before it was sold. Today I found new sump strainer and side oil filters installed. All screws in place but not tightened. Oil drain plugs finger tight and obviously, no oil in the engine. All is now reassembled with new gaskets and ticked off the list.

But...... Inspection of the points and auto advance unit leaves me a question that I'd like an opinion on please.

The points and the auto advance unit itself look recent. Everything is free enough and after a light oiling where appropriate, it seems good to go. Except - there's no preload on the bob weight springs at all. The bob weights are easily moved to full advance and there's little if any wear present. But - the bob weights are not pulled back to the retarded position by the springs. It seems to me that auto advance functionality is fine. But I fear as soon as the motor starts, it will be fully advanced on ignition timing. Does that sound right? The bob weights can be easily moved with virtually no force, they just don't seem to auto retard the way I imagine it should.

Does it sound like the springs are a tiny bit too long? Thanks.
 
Well a strobe light .would give info .
Can find them used for cheap since they are out of use ,Nowadays If i does not retard it can stall at stoplight and so
I had worn advance unit and weak springs machine ran perfect
Springs was possible to buy back then
To much advance is not good
 
Jan_P said:
Well a strobe light .would give info .
Can find them used for cheap since they are out of use ,Nowadays If i does not retard it can stall at stoplight and so
I had worn advance unit and weak springs machine ran perfect
Springs was possible to buy back then
To much advance is not good
Click to expand...
Thanks. Yes, I might have to wait until it's running and see if it goes fully advanced at tick over with a strobe light.
 
Its been a long time said:
Thanks. Yes, I might have to wait until it's running and see if it goes fully advanced at tick over with a strobe light.
Click to expand...

I dont think it will advance at tick over just a little .perhaps
But it advances sooner to full advance at throttle up -- but I believe there is a stop post if everything is OK
That is what I suspected was so good for the running :At full power with the XS a quicker response ( No investigation done )
Then letting go going down in RPM was when it went wrong it would not retard .. and stall at Stoplight
And not retarded difficult to start again Kicking like a fool at the Intersection listening to some car Horns
Back then I did not know of the need service for the advance rod . And it was worn so I replaced with Boyer Bransden
But I still have the feeling it ran better with those sloppy springs .
Again to much advance and there can be holing of the piston Dangerous .But Bike it ran well Like a Scolded rat
 
Jan_P said:
I dont think it will advance at tick over just a little .perhaps
But it advances sooner to full advance at throttle up -- but I believe there is a stop post if everything is OK
That is what I suspected was so good for the running :At full power with the XS a quicker response ( No investigation done )
Then letting go going down in RPM was when it went wrong it would not retard .. and stall at Stoplight
And not retarded difficult to start again Kicking like a fool at the Intersection listening to some car Horns
Back then I did not know of the need service for the advance rod . And it was worn so I replaced with Boyer Bransden
But I still have the feeling it ran better with those sloppy springs .
Again to much advance and there can be holing of the piston Dangerous .But Bike it ran well Like a Scolded rat
Click to expand...
Thanks. I can move the advance rod to full advance and there's little if any spring tension. It all looks good and in fact I would say quite recently new. I think the springs are maybe 1 or 2mm too long. Maybe tomorrow when it's light I can take a couple of pictures to show what I see.

I would be interested in knowing if there's anyone out there had a similar finding to me when looking at the auto advance unit.
 
I think that at the point of your rebuild you should not worry that much about the auto advance device.
But, before trying to start the engine, do the static ignition timing with the auto advance in full retarded position and then check the timing in full advanced position.
Then you can safely start the engine and then, if you have any doubt, you can check the advance with a strobe.
 
Weights should snap back. I replaced the springs on my weights when I bought the bike thinking replacing old with new has to be preventative maintenance. Weights didn't snap back and almost didn't close up completely. I put the old ones back in.

At the time, I read a while after, MikesXS springs were to long and people were cutting of a coil or 2 to get the tension back.

That was a long time ago so can't say that it is still a MikesXS problem.

Might b a solution to cut the springs .
 
650Skull said:
Weights should snap back. I replaced the springs on my weights when I bought the bike thinking replacing old with new has to be preventative maintenance. Weights didn't snap back and almost didn't close up completely. I put the old ones back in.

At the time, I read a while after, MikesXS springs were to long and people were cutting of a coil or 2 to get the tension back.

That was a long time ago so can't say that it is still a MikesXS problem.

Might b a solution to cut the springs .
Click to expand...
Thanks. That's what I thought. It's even possible that the bike has the springs fitted from MikesXS, they definitely don't look 47 years old. There's no history on the bike but it's clear the previous owner put a lot of new bits here and there before selling it.

In the UK I can buy new springs from Yambits. But first I'll take mine off, measure them and ask Yambits to confirm what theirs measures. Unless their springs are a mm or two shorter, then I'll shorten what I have.
 
I have some N.O.S. originals I could measure. Managed to find them on eBay. The originals on my bike are a bit loose and sloppy but still seem to work fine. I do keep the advance rod well lubed, which I'm sure helps.
 
5twins said:
I have some N.O.S. originals I could measure. Managed to find them on eBay. The originals on my bike are a bit loose and sloppy but still seem to work fine. I do keep the advance rod well lubed, which I'm sure helps.
Click to expand...
Yes please, if it's not too much trouble for you. :)

I looked on eBay last night, there's nothing at the moment.

The advance rod is really free, no stickiness there. Nor on the bob weight pivots.

I am going to take another look this morning. If I can, later, I'll upload a short video here of the assembly and what it does.
 
OK, just had a closer look at the auto advance mechanism now it's bright daylight. Quite obvious that the right side spring has been over extended, it's doing nothing. The E clip is missing off it too. The left side spring isn't obviously over stretched but neither is it strong enough to pull the bob weights back on it's own. The mechanism looks in great shape. But it's obvious I'm going to have to do something with the springs and find a new E clip from somewhere.

As far as I can see on Partzilla, there's no Yamaha part number for the E clip or the spring.

Here's a short video, if it works -

Auto advance video
 
Mine looked a little loose also but the bike ran fine.
That one spring is obviously not doing anything but the other is stretching.
Remember though, with the bike running and the engine vibration going on
might help pull it back into position at idle. I interested to see measurements also.
Might be able to order from Grainger if none 650 can be found.
 
JOHNDADDY said:
Mine looked a little loose also but the bike ran fine.
That one spring is obviously not doing anything but the other is stretching.
Remember though, with the bike running and the engine vibration going on
might help pull it back into position at idle. I interested to see measurements also.
Might be able to order from Grainger if none 650 can be found.
Click to expand...
There's lots of springs out there but it'll be a lottery what the resulting advance curve would be with an unknown spring. At this point, with the E clip obviously missing, I don't think I have a great many options. Probably have to buy the spring and clip set from Yambits. Link -

https://yambits.co.uk/xs650se-auto-advance-governor-spring-kit-points-models-only-p-164593.html
 
JOHNDADDY said:
Nice, bookmarked it. I don't think it would hurt to replace mine.
Click to expand...
My guess is that globally, everyone selling these springs and E clips is selling the same thing? There can't be enough demand for multiple sources for these parts to be viable? (I noticed a lot of the stuff Yambits sells is marked up as from EMGO when it is delivered).
 
It would be a nifty thing for someone to measure the spring force on these for posterity. Hook a spring to something to suspend it. Then add a small known weight and measure how much it moves. Your target weight would be something that makes the spring move about 30-70% way of max movement of the weights
 
Advance mechanism has stiction and thus hysteresis.
This shows up on all mechanical flyweight machines from governors to distributors.

Those not knowing how to run distributor machines for spark advance "optimization" fall into this trap.
Advancing is one curve.
Retarding is far above the advance curve at lower rpms. They curve from low to high speed only, not knowing stiction.
Secret is to blip or interrupt dist. mach. motor to mimic engine rpm changes through 720° .

Run the engine to find real timing.

cliff
 
Melnic said:
It would be a nifty thing for someone to measure the spring force on these for posterity. Hook a spring to something to suspend it. Then add a small known weight and measure how much it moves. Your target weight would be something that makes the spring move about 30-70% way of max movement of the weights
Click to expand...
Pounds per inch would have been the standard.
You don't have to stretch it an inch, obviously.
Grams per mm is kinder to it :)
 
These are the replacement e-clips I've been using. They fit and work well. So far, I haven't had one fail. It's handy to have extras on hand because sometimes an original will break when you try to remove it, or fling off across the garage never to be seen again, lol. For a few dollars, you can get a lifetime supply of replacements .....

AdvanceE-Clip.gif


AdvanceE-ClipSpecs.jpg


I'll try to measure those N.O.S. springs I have later today.
 
5twins said:
These are the replacement e-clips I've been using. They fit and work well. So far, I haven't had one fail. It's handy to have extras on hand because sometimes an original will break when you try to remove it, or fling off across the garage never to be seen again, lol. For a few dollars, you can get a lifetime supply of replacements .....

View attachment 264274

View attachment 264275

I'll try to measure those N.O.S. springs I have later today.
Click to expand...
Wow. Fantastic. Thanks so much.

Pack of 10 on the way to me.
 
Last edited:

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