RM 125 no power at full throttle

[huskibul]

      Black Box ! 

[Simo63]

      Black Box ! 

Great 90's dance music group .. think I have one of their albums somewhere 

[huskibul]

    Yeah i think it's about track 4 = "Flat spot on top" - not real good to boogie to from memory 

[PCMAX]

Thanks again guys for all the suggestions. Think I have eliminated all of the carby breather/needle & seat problems by installing another 32mm Mikuni but it made no difference at all to the performance.

I originally (about 18 months ago) had problems with the OEM stator coil so I had it tested by Small Coil Rewinds, they found one of the two coils to be faulty and rewound it for $120 a couple of meetings later it started playing up again so I sent the coil to a guy called Andy Wheeler on the central coast, he found that the other of the two coils was faulty and rewound that for me for another $120. Not long after that it started coughing & farting again & rather than spend another $120 I put a spare stator coil from an 82 CR125. That has worked well for over a year and produces a strong spark. During this period I also bought an aftermarket coil from RM Stator in Canada, that lasted just one meeting at Canowindra in 2010. At least the guy refunded my money but i had to pay $36 to send it back to Canada.

When it first started playing up in March this year I immeadiately suspected the stator coil and swapped it with the one I have in a running '82 CR125 but it made absolutely no difference to the problem so I eliminated that as the issue.

Anyhow just "to be sure, to be sure," I have ordered an aftermarket OEM copy from Rick's Stator in the USA and will fit that when it arrives and let you guys know what happens

[Simo63]

I've been following this post with interest to see what the problem works out to be and only now noticed that you have declared you are running CR125 ignition parts.  Is that right or do I need to go and lie down?  Surely the parts are not going to be compatible?  If it's an RM125 then surely youwould use RM125 parts only, even if ignitions from other makes/models fits, they still might not be compatible.  Maybe I'm wrong (been wrong more times that I can remember) but I can't see that ignitions systems and particularly component parts are too interchangeable.

I recall using the services of Small Core rewinds (in Geelong) once back in the early 90's when my RS125 developed an ignition problem at around 12,500 rpm that resulted in my exhaust pipe continually splitting.  Is the owner still Bert Neville (or a similar name)?  I would personally stick with them on ignition matters, or at least stick with the one supplier.

And it also sounds like you've had an ongoing issue with ignitions.  Personally I've never heard of such a continuance of problems ... is there something else going on that you haven't mentioned yet?

Sorry just asking to see if some more information comes to light as I believe your problem must be frustrating the hell out of you.

[Lozza]

Simo, all high voltage CDI's work the same way, coil specs are within a few 100 Ohms of each other, the only incompatable bits are the wiring and how the kill switches work.Sounds like the complet ignition was swapped over. Bert Neville might be able to fix and repair coils but unfortunately his ignition knowledge on 2T engines ends there. Your RS would have been over retarding and firing on or after TDC causing fuel to ignite in the pipe(RS's retard off to about 5deg BTDC at that rpm).

Has anyone got a report on the air gap the spark will jump? If not you wasting good money after bad with all the repairs etc etc. That is what determines the health of the ignition. Min is 5mm there is no maximum.

[Simo63]

Simo, all high voltage CDI's work the same way, coil specs are within a few 100 Ohms of each other, the only incompatable bits are the wiring and how the kill switches work.Sounds like the complet ignition was swapped over. Bert Neville might be able to fix and repair coils but unfortunately his ignition knowledge on 2T engines ends there. Your RS would have been over retarding and firing on or after TDC causing fuel to ignite in the pipe(RS's retard off to about 5deg BTDC at that rpm).

Sorry Lozza but I must have misread the OP's post.  I though he said he replaced the stator coils with CR items .. isn't that the coil on the stator plate, screwed to the LHS of the motor?  Surely they aren't the same for RM and CR?  Or are stator coils what I would call the ignition coil (eg under the tank area that the spark plug lead eminates from)?

And the RS ignition was definately faulty and sporadically advancing and then retarding as much as 13 degrees which was the source of all the problems .. I won't go into the full blown story in detail here but it was character building stuff apparently 

Anyway, needless to say I learnt how frustrating ignition problems can be so back to the original post and lets see if we can help PCMax before it gets too much for him.

[huskibul]

    The earlier 76-78' RM two piece stators were physically the same as the CR's , and even the later model bridged ones  fitted -79' thru early/mid eighties 

[Simo63]

    The earlier 76-78' RM two piece stators were physically the same as the CR's , and even the later model bridged ones  fitted -79' thru early/mid eighties 

This is one of the things I love about this site .. something new to learn every day.

Has anyone got a report on the air gap the spark will jump? If not you wasting good money after bad with all the repairs etc etc. That is what determines the health of the ignition. Min is 5mm there is no maximum.

Lozza could you please explain a bit more about this.  Are you saying the spark needs to be able to jump at least 5mm to be considered good?  Is that just on kick over?

[Lozza]

Simmo, ignition problems should not be frustrating at all. I'm yet to even read where  the engine has been strobed with a timing light. That is the most basic check you can perform, I fail to see how you can do without a timing light for setting up or diagnosing an engine.
Overview.
The ignition coil merely amplifies then dumps voltage to the plug. The source and pulse coils are located on the stator, they provide the voltage for the spark and a small trigger pulse, so the CDI can tell the coil to dump to the plug. The position of the magnets in the flywheel say when the trigger pulse is timed.
It does not matter 1 aviating sex act who made the ignition,pulse or source coils what matters is WHEN it sparks in relation to TDC.
The igntion 'curve' is controlled by the CDI it will have a maximum amount of advance, and retard from there according to RPM. The ignition cannot predict the future.
So we come to the air gap. First I'll ask this question under what condition is the spark attempting to jump from the J strap to the centre electrode?

[Simo63]

Thanks for the informative learnings Lozza, ignitions and wiring in general always seems complex to me mainly becasue I have never learnt or understood them.  Hence I guess the potential frustration. 

So we come to the air gap. First I'll ask this question under what condition is the spark attempting to jump from the J strap to the centre electrode?

I'm not sure what you are asking here.  I thought you were saying that the spark needs to be able to jump a minimum of 5mm to be considered a good spark.  Did I get that wrong?

Sorry to PCMAX for getting a bit off topic but maybe these questions will help him as well?

[Lozza]

Yes the spark needs to jump a min of 5mm air gap, but what I'm asking is WHY do you think it needs to be able to jump a 5mm air gap to be considered healthy.

[pancho]

Because the resistance across the plug gap increases in accordance with the increased compression pressure as the volumetric efficiency reaches its max.

[Mike52]

The igntion 'curve' is controlled by the CDI it will have a maximum amount of advance, and retard from there according to RPM. The ignition cannot predict the future.

I use a strobe to set  my timing on all my engines and have noticed that there is no advance at any revs on my 2/stroke huskys .
The mark stays exactly where I have set it from idle to flat out.
Do I have a problem ?
Mike

[Lozza]

Because the resistance across the plug gap increases in accordance with the increased compression pressure as the volumetric efficiency reaches its max.

 Basicaly, the plug must fire under pressure and turbulence also at higher rpm with less time to recharge the capacitors.

I use a strobe to set  my timing on all my engines and have noticed that there is no advance at any revs on my 2/stroke huskys .
The mark stays exactly where I have set it from idle to flat out.
Do I have a problem ?
Mike

Just means you have a fixed advance ignition