strange timing

someone at some point had installed points on my 79 1000st. i replaced them using a dyna s kit. while setting timing with my adjustable light, i noticed i do not have advance marks, just the "t" and the "f" marks. the difference between these two marks is 40 degrees, confirmed by the adjustable light. does this seem strange? if i were to set to the f mark at idle, it would be 40 degrees advanced at 1000. owners manual calls for 10 degrees at idle and 40 at 3600. so in this instance, should i set to "f" at 3600? i went ahead and timed it today by setting the light to 10 degrees and using the "t" at idle. when i rev the engine, the "f" just about lines up.

Hi, zbucket! And welcome to kzrider!

With regard to setting ignition timing:
At slow idle rpm, F-mark should line up with mark on engine casting. When blipping throttle, should be able to see advancer unit in actual operation. And don't worry about trying to line up any marks at full advance.

Ignore the T-mark (which shows TDC or Top Dead Center)because setting ignition timing does not involve the T mark.

The T mark is useful when doing cam chain adjustment, because rear side of the cam chain has most slack at TDC and better enables the "automatic" adjuster to remove "excess" slack.

Good luck!

thanks for the welcome! i actually used to belong under a different name but forgot what it was long ago :blush:

doesn't TDC have everything to do with timing? such as the specs calling for 10 degrees before TDC? i know i'm over analyzing, but i like to figure out why things are a certain way the way i'm looking at it, if i set the timing at idle on the "f", i will be setting it at 40 degrees BTDC. maybe the electronic ignition changes the desired spec?

thanks!

Stated another way, TDC is zero degrees BTDC.

At apx 1350 rpm idle speed, the plug is supposed to fire at 10 degrees BTDC. This is where the F-mark matches the case mark. It is the least advance position and is where the springs are holding the centrifugal weights on the advancer unit completely closed.

As rpm's increase, the degree of advance increases from 10 degrees BTDC at 1350 rpm to its maximum advance position of 40 degrees at 2500 rpm. This happens because as rpm's increase, centrifugal force overcomes the springs allowing the weights to spread apart until the weights are spread to their limit at 40 degrees BTDC.

At apx 2000 rpm, the advancer unit has partially advanced (the weights have partially spread) so that the plug fires at 20 degrees BTDC.

So yes, TDC is important as the zero position from which advance measurement begins. But the F-mark is used to set timing at idle rpm because when the F-mark matches the casing mark, the advance at idle rpm is then correctly set so that the plug fires at the designed number of degrees BTDC. The further advancing to 40 degrees at 2500 rpm will take care of itself via the centrifugal weights as the weights spread out against the springs.

Btw, you aren't the first (and won't be the last) person who incorrectly used the T-mark as an ignition timing reference.

The above figures are shown on a chart in the FSM text; however, the spec sheet shows 10 degrees at 1000 rpm and 40 degrees at 2350 rpm. Regardless, use the F-mark at idle speed.

Post edited by: Patton, at: 2007/11/12 02:41

The Dyna S uses the same timing specs as the stock system.

The timing light is calibrated for crankshaft degrees assuming one spark per two revolutions (old car with distributor). The KZ has one spark per one revolution. You have to divide the knob reading by two. If your knob is set to 40 when your T mark is lined up, you are firing at 20deg Before TDC.

This agrees with the 1977 KZ1000 specs here:
kzrider.com/content/view/89/50/

It also agrees with several other sources I found for the 1977 on the net in a quick search.

Perhaps someone put an advancer from another year (77 or 78?) on your bike?

You should probably pull out a plug and feel for TDC through the spark plug hole to verify TDC is actually when the T mark lines up, in case the different advancer doesn't have compatible marks.

Post edited by: loudhvx, at: 2007/11/12 03:35

patton's explanation confirms what i was thinking. loudhvx....dividing the advance numbers on the light by two makes complete sense. i did verify that "t" is actual TDC.
i will use the "f" mark at idle. so instead of it being 40 degrees from TDC it is 20 degrees.

thanks guys!

zbucket, Welcome. Perhaps the mechanical timing advance that was used with the points was from the original bike. It will not have an F mark at all for the 2/3 cylinders; only a T. Get a mechanical advance from a later points-equipped bike with the full set of markings... it will be much easier to time the bike accurately...

Guess what I am getting at is that the IC Igniter mechanical advance was used on a bike where timing can not be adjusted so the 2/3 positions didn't have the F mark... I don't recall if 1/4 did or not but get an earlier advance.

Post edited by: wiredgeorge, at: 2007/11/12 11:01