Mechanical advance ???

[racerdave]

The rod can be turned back and forth with my fingers to the weights full advance or full return. The weights move freely. Should springs pull the weights completely back to the stops? One spring definately has less tension than the other.

 

[pamcopete]

racerdave,

Here is what the advance should do:

 

[racerdave]

Pretty much what I really knew. Just wanted to be sure. Been years since I messed with any mech advances. Are Mikes XS spring kit good, or are oems still available, or any off the shelf from Napa/Autozone/Pepboys a retro fit??

 

[retiredgentleman]

I had the advance springs from Mikesxs, and I did not like them. The advance was not linear. The engine would bog down initially, and then the advance weights would snap open and acceleration would come on real strong. I may have caused part of the problem, because I cut 1 coil off the springs.

I put my OEM stock springs back on (never throw out any parts you remove from your bike), and the acceleration is linear. They work perfectly.

I don't know if OEM springs are available, but definitly you should try to get some.

 

[racerdave]

retired, was there a reason you cut the new springs to start with?

 

[retiredgentleman]

Yes, I was having trouble with a hanging high idle. It turned out to be air leakage............carb shaft seals and Mikesxs manifolds. Mikesxs manifolds fit very poorly and allow air inleakage..................I re-installed my original OEM manifolds and they work perfect.

 

[XSLeo]

You can adjust when the weights open by adjusting the spring tension.
With your springs as is, shoot the timing marks with a timing light. Rev the engine, paying attention to the rpms the advance hits full advance.
it should hit full at 3200 rpms.
If it hits full at more rpms the spring are weak. If at less rpms to strong.
To weaken the springs stretch them a bit. If weak, clip of the loop and bend up next for a loop. Do one spring at a time.
It may take a few tries.
Leo

 

[pamcopete]

OK. When the springs are weak, the advance will move out at idle and use up some of the available movement of the weights which results in there not being enough advance available at full advance, meaning that you will not achieve full advance with weak springs, but you will achieve whatever advance is available sooner..

If the springs are too strong, then you will not achieve full advance at 3,000 RPM, it will occur at higher RPM's, or perhaps not at all if the springs are really tight.

So, weak or strong springs results in not achieving full advance at 3,000 RPM.

All of this without any excessive mechanical wear on the weights pins or the little knobs that engage the slots in the slotted disk and presuming that you have set the idle timing on the "F" or "U" mark.

Think of it this way. If you removed the springs, the weights would fling out at idle, and you would dial the timing back to the correct timing mark, if possible. That would leave no more movement of the weights when you increased the revs, so you would not achieve full advance. Having no springs at all is an extreme case of very weak springs because the weights are free to move.

 

[cros36]

let me throw a wrench into the mix for you guys....

can too loose or too tight of springs cause harder kick starting?

 

[pamcopete]

let me throw a wrench into the mix for you guys....

can too loose or too tight of springs cause harder kick starting?

Not too tight. But too loose will allow the advance to advance while you are on the downstroke and fire the cylinder before its time, like, the piston will go back wards and kick back.

 

[CDNTX650]

mine is timed where it should be, although i did have to time to full advance and doctor it with a small amount of jb weld on the weights to not retard so much (worn out over advancing, new one coming), idles right low at 1100 no creeping up, at about 3100 rpm it advances. once in a while i do get a kick back....not really sure why....i don't kick straight legged so it does nothing to me. Any reasons why? running the dual output coil, single points lobe from mikes...new battery, charging system is good, all rewired and new fuse block.

 

[pamcopete]

Kickback can be a result of dirty points. As you depress the kicker, the points make contact, but then, because they are dirty, the points effectively open, which produces a spark at the wrong time.

The PAMCO does the equivalent of closing the points, but there is no mechanical opportunity for the PAMCO to "open the points" unless you rotate the engine forward 120 degrees or backward 300 degrees, so there is less opportunity for a kick back.

 

[CDNTX650]

haha, should be clean as a whistle. i clean em anytimei clean the bike or do other maint. next step after advancer replacement is pamco.

 

[racerdave]

OK. When the springs are weak, the advance will move out at idle and use up some of the available movement of the weights which results in there not being enough advance available at full advance, meaning that you will not achieve full advance with weak springs, but you will achieve whatever advance is available sooner..

If the springs are too strong, then you will not achieve full advance at 3,000 RPM, it will occur at higher RPM's, or perhaps not at all if the springs are really tight.

So, weak or strong springs results in not achieving full advance at 3,000 RPM.

All of this without any excessive mechanical wear on the weights pins or the little knobs that engage the slots in the slotted disk and presuming that you have set the idle timing on the "F" or "U" mark.

Think of it this way. If you removed the springs, the weights would fling out at idle, and you would dial the timing back to the correct timing mark, if possible. That would leave no more movement of the weights when you increased the revs, so you would not achieve full advance. Having no springs at all is an extreme case of very weak springs because the weights are free to move.

Pete, on the bold, I disagree somewhat or think that this somewhat misleading? As long as the weights move freely, and their full travel is there from stop to stop, due to centrifugal force, you will get full advance just not in a linear curve or at the correct rpm.

 

[pamcopete]

racerdave,

With weak springs, the weights will move out a bit at idle speed. This results in a slight advance at idle. So, you would then adjust the timing in the retard direction to obtain the correct timing at idle. Now, the timing is set at idle, but some of the available advance movement of the weights is already used, leaving less for full advance.

Think again of my example of no springs. Removing the springs is the equivalent of very loose springs. With no springs, the weights would move out to the stops at idle and would not move any more with an increase in engine speed. However, you would still attempt to set the timing at idle with the weights fully extended leaving zero available movement at higher RPM's.

Another way to look at it is to set the timing at full advance to the full advance mark with weak springs. When you then reduce the engine speed, the timing at idle would be advanced because the weak springs would not fully retract the weights.

Here's another way to think of it. The only way that you can achieve the full range of advance from idle to full advance is if the weights do not move at all at idle, which is the case with having the correct tension in the springs.

 

[jefft]

Oh great, all this talk about possible weak springs from Mikes and I just ordered parts to install advancer and Pamco to replace my Boyer. Does anyone know of a source for springs other then Mikes?
jefft

 

[jefft]

Just wondered if anyone has checked springs used in autos? Companies like Mr. Gasket, Mallory have spring kits with various spring tensions for fine advance curve adjustments. jefft

 

[racerdave]

I just bought a pack of 5 springs on Ebay, that a member posted about in a different thread I started.

 

[pamcopete]

Oh great, all this talk about possible weak springs from Mikes and I just ordered parts to install advancer and Pamco to replace my Boyer. Does anyone know of a source for springs other then Mikes?
jefft

jefft,

If you have bought the complete advancer from MikesXS, then that is the advancer that I used in the above video showing correct "snap back" so it will be fine.

 

[pamcopete]

Here's another controversial item:

I think of the advance mechanism more as a retard mechanism because the engine spends most of its productive life above the max advance speed, so the "advance" mechanism is really there to make it easier to start the engine and idle at low engine speed by retarding the spark advance.

As far as a sophisticated advance "curve" goes, it only changes between 1200 RPM and 3,000 RPM, only 1800 RPM out of the available range. Plus, the advance on the XS650 is just a speed driven system, there is no reference to engine load, like a vacuum sensor, so you are limited in the maximum advance that you can safely use.

There are some motorcycles that have a load sensor, and all cars have one as well, either a vacuum sensor or a MAF sensor so the ignition advance curve on these vehicles is really sophisticated to squeeze out as much HP and MPG as possible. The XS650 does not have any load sensor at all, except for the carb slides that are vacuum operated, but this information not passed on to the ignition system.