TM125 timing issues

[brent j]

My TM125 kicks back when you start it. It's a short sharp kick back and if
your not kicking hard enough it will stop the kick start lever dead!
So far I've broken teeth off two kick start idler gears, The last one was
brand new and lasted about 2 hours tops!
It appears the timing is far too far advanced but it sits there and idles quite happily.
I've had to slot the backing plate to retard it enough get it to run (quite
well too, now!) and be able to start it. It’s better now but still not right.

The stator, rotor and CDI are from unknown sources. I've had them tested and they are supposed to be ok.
With the timing set on the factory marks it is way too far advanced and
starting is a nasty exercise.
Put a timing light on it and it's not quite on the factory marks. Moving the
backing plate will obviously change the timing but as the timing marks and the ignition pick up are both on the backing plate the timing indication doesn't
change.

I've been told the timing should be 19 degrees (@6000 rpm) BTDC or 1mm but the RM manual I have a copy of says 29 degrees or 3.8mm. The TM and RM share the same ignition..
The next thing will be to make a plate to (temporarily) bolt to the
centre case to show true timing marks, both TDC and 19 degrees.
Any ideas guys?
The motor is pretty well stock (as far as porting and tune) with only a fresh bore, piston, rings and blue printing and careful assembly.
The piston is an aftermarket CR125 unit so I'm not sure the dome height is the same. I’ll have to check this. Also the bottom of the intake port was lowered to compensate for the longer piston skirt.
Comp is not excessive and it turns over as I would expect with the plug cap off.
On the off chance, what comp should I expect when kicking it over?

The next thing is,
I bought a CDI on ebay. It's new and advertised as a TM125 unit. The part No is #####-28700 which doesn't exist whereas the TM one is #####-28700 (or vice-versa). It is labelled as TS125 but all the TS125’s I've ever seen had points.
I've run this unit and it works but there is no advance/retard with revs. Does
the TM125 CDI alter the advance? if so which way? advance or retard? has anyone else tried one of these ebay units?

Any help appreciated

Brent

[brent j]

I think I’ve just solved my problem.
Because I had to retard the timing I’ve been fixating on an ignition problem when it looks like the real cause was too much compression.
I’ve just compared the piston dome heights between a CR piston and a TM piston and the CR is slightly higher but also more rounded.
The book says the corrected comp ratio should be 7.5:1 (about 110psi) and I’m guessing it’s a bit more than this.
As my XT has a 10.5:1 piston it’s a bit hard to judge just how hard the TM was to kick over………………………………….

Funny how when you write something down it starts to make sense.

Brent

[mainline]

Glad we could help

[DR]

Brent I was at a loss with the ignition probs in all my years of rooting with Suzuki's I've never had anything like those issues you described. I did see that 'TS125' CDI unit you have, I think Paul Miller or Mike Armstrong had it on fleabay US. I could never work out what it was from either, it's the later mid 70's onward RM shaped black rectangular Nippon Denso item at a time when Suzuki were using mainly Kokosan with the squarish black plastic jobs yes

Thicker head gasket or get used to bump starting eh

I always thought there was a minor difference in the dome on the CR pistons but then I also heard of people using them in TM's with no mods   erred on the side of caution and purchased genuine TM/TS/RM or Wiseco equivalents. Side by side on a bench and it's noticeable by eye which had me in 2 minds.

Those forks springs shouldn't be too far away either..posted last Friday

[trailietrash]

It is labelled as TS125 but all the TS125’s I've ever seen had points.
I've run this unit and it works but there is no advance/retard with revs. Does
the TM125 CDI alter the advance? if so which way? advance or retard? has anyone else tried one of these ebay units?

Any help appreciated

Brent

The 1980 TS125 had a pointsless ignition. But the CDI and coil were one unit.

Most 2 stroke CDI's (or points) ignitions of this era don't have an advance unlike 4 strokes.

How did Suzuki set the timing marks on the backing plate at the factory. Does the TM have a mark in the centre? There are two marks on some backing plates for the different timing to suit the RM125M and RM125S.
Is the 19 degrees for the TM at 6000RPM as is the 29 degrees for the RM? I don't have any TM reference material with me at the moment so I can't cross reference these but check both degrees and RPM and don't just compare degrees. If there is a mark to the right of centre on the backing plate then set the timing at this as it may be closer to the TM timing.