1981 RM125X Ignition Timing

[PCMAX]

Does anyone know the specs for the ignition timing for a 1981 RM125? ie firing point in mm or degrees BTDC @xxxx RPM

[lukeb1961]

17 +- 1  BTDC @ 10000

[PCMAX]

Luke,
do you mean 17 degrees BTDC? I'm a bit of a novice at this but If the stroke is 54mm then one 360 deg revolution of the crank would see the piston travel 108mm. For each degree of rotation the piston would travel 0.3 of one mm. If the firing point is 17 deg BTDC that would mean 17 x 0.3 = 5.1mm. That seems to be a hell of a long way BTDC. My '75 250 Elsinore fires at 3mm BTDC I would have thought a 125 would fire at less that 2 mm.

Any clarification would be appreciated.

Thanks
peter

[tony27]

Having a conrod means that the piston travels a different amount depending on where in the stroke it is, close to top & bottom dead centre it moves a smaller amount per degree of rotation than it would around mid-stroke. Using a degree wheel is the most accurate way to set timing because of this

[LWC82PE]

Ignition timing is 17 DEGREES before top dead center @ 10,000 RPM
straight from suzuki specs book

[Lozza]

Degree wheels have a fairly high 'degree' of inaccuracy as well. Best is software (Excel spreadsheet etc)then trig and mm off TDC far more accurate. Rod length and gudgeon pin offset also plays a part but you ar correct tony.

I just run that through the calculator and 17deg btdc
for 54mm stroke 100mm rod length=

ta da
1.49mm BTDC

Even easier is my timing light I just mark off TDC and input the degrees when the marks line up advance is the indicated degrees

[lukeb1961]

Even easier is my timing light I just mark off TDC and input the degrees when the marks line up advance is the indicated degrees

Lawrence, I have an issue with my timing light - it shuts down way before 10,000rpm.  What are you using?
Luke

[Lozza]

An ultra rare, cold war, smuggled out from behind the Iron Curtain, as used by works teams, unobtainuim  INNOVA EQUUS 

* just find a seller that ships o/s these sign off at 9999rpm to but very good up to that point.

[lukeb1961]

no doubt a modern Japanese copy of Walter Kaaden's original valve-powered model spirited out from Zschopau - as used in the 1960 GP!

many thanks.
Luke

[LWC82PE]

Does this sort of digital timing light require its own external 12v DC power source to run? I wouldnt imaging it will run straight off the AC signal from the magneto or HT cable??

[Lozza]

Yes needs 12v DC.