Advance mechanism: weights don't snap back

[QTreiber]

Hello,

I had an issue with high rpm's when the engine of my 1979 XS650 Special II was hot. I checked the advance mechanism and found that the weights don't snap back.

I cleaned and lubricated the advance mechanism: pulled the rod, cleaned and lubricated it, replaced the springs (used new springs from Mike's XS), lubricated the "pivots" of the weights.

The weights still don't snap back. Could the new springs be too weak or could there be another issue?

Thank you,
Armin

 

[wherearewe]

Could be the new springs. I put in a NEW OEM ATU and that actually caused a hang up (a problem i never had until then and the snap felt pretty weak). I guess age of the springs - dunno??? It did fix my advance range issue though...

Mikes springs have a reputation for being weak. Simple fix - Try cutting out one loop of ONE spring and making a new hook. Test. Thats what i did.

 

[DogBunny]

I concur. Cut one loop off of one spring. This is "standard" procedure when using MikesXS advance springs. If the advance mechanism still wont behave, cut one loop off of the other spring.

 

[Tomterrific]

The point cam turns with the advance mechanism. The point heels rubbing friction on the cam can hinder the advance snapping back solidly when not running. When the engine is running this friction 'pulls' the advance back to full retard. I have seen this as a common symptom even after the mechanism is lubed and otherwise works fine but it is better to have the springs putting some tension on the weights at full retard, just not too much.

Tom

 

[pamcopete]

QTreiber,

tomterrific has a point (pun?). If you are referring to the video that I put on YouTube showing proper snap back, that was intended primarily for the PAMCO whose rotor replacement for the points cam does not come in contact with anything to produce the equivalent drag that you get from the points rubbing block. To do the snap back test with a points installation, temporarily prop the points open with a piece of thin cardboard so the rubbing blocks don't come in contact with the points cam.

 

[QTreiber]

Thanks, guys, I appreciate the advice! Yes, I was wondering, how much drag the points cam would contribute.

I will prop the points open and see what happens. Depending on the outcome I will shorten one spring.

Greetings from Colorado,
Armin

 

[QTreiber]

I propped the points open and now the weights return ~80%, but don't snap back, it's a somewhat sluggish return. The engine is cold and the grease is quite viscous.

I guess an 80% return is not good enough. I will shorten one spring. In case I mess up the spring are there any other sources than Mike's?

Thanks again,
Armin

 

[weekendrider]

Occasionally they come up on ebay.

 

[pregrid]

Speed and Sport Yamaha

 

[wherearewe]

From my research you have to buy a whole governor unit if you want OEM - springs not stocked separate. I might be wrong. If they are not snapping back when the engine is off, they wont work properly once its spinning with centrifugal forces etc etc. Could be bob weight and disc wear compounding old springs. Maybe consider a replacement mikes unit?

 

[Hairyblackdude]

I installed a Pamco on my bike a few months ago & had an issue with the weights not snapping back.

I removed the advance spring setup from the 1 side and was just spinning the rod with my hand. It was very easy to spin with my fingers, but just got a little bit tighter in this 1 spot. I lubed it several times with a few different types of lubricant, but always seemed to hang slightly.

I ended up taking a piece of 400 grit sandpaper & wrapping it around a 1/4" ratchet extension. Used my drill at a low speed & just ran the sandpaper in the bushings a few times.. In and out, back & forth.. Barely removing any material at all, just smoothing it out..

Blew out any debris, after reinstalling the rod, it was spinning freely and easily with my fingers. The weights snap back with authority !!