Coil voltage

[bufallobiff]

I've got a RT 125 that hasn't run in a good while. I could never find the problem. Compression good at 145 psi and I get a spark at the plug. I can spray either directly into the intake with the carb off and it won't even fart. Whether or not I'm getting a proper spark I have no way of knowing. Most M/Cs I've dealt with supply 12V at the coil when the ignition switch is turned on. This is not the case with this MZ. Does anyone know what voltage is supposed to be there? I've got two CDI boxes and neither supplies 12 V. Somehow, I read almost 50VDC at the coil with a reversed polarity from the CDI box to the coil. I'm using an analog meter (Triplett) so I'm pretty sure it's not lying. I can't imagine that the valve timing is off because it was running one day and wouldn't start the next. Are there timing marks to line up just to check valve timing?

[michael]

you cannot find a voltage there because the CDI contain a capacitor (capacity ?) supplied at more than 200V and il is connected to the coil (at the right moment !) so it is very short and cannot be read by an analog voltmeter, may be a numeric meter can ?

you said you read reverse 50VDC it may be true because the coil give back some curent, except that there is a diode in the CDI wich short this reverse current to the ground

so the best way to know if the CDI works is to unscrew the spark plug and look if there are sparks when running the motor (don't forget to put the ground part of the spark plug on the ground of motor (excuse me for my bad english I'm french)

I own 2 RT, we have a forum in France : http://forum.moto-mz.fr/search.php?action=show_new

...... because it was running one day and wouldn't start the next : not a proof ! you'll be alive before dying (bad humor, I know)

[DAVID THOMPSON]

never had a problem with the cdi on mine
but the carb goes dry after setting for a few days and it can be a beast to get started
dave

[michael]

sorry bufallobiff I didn't pay attention you wrote that you got sparks

so the carb can be responsible

another problem we had twice : a chain wheel on the camshaft has slipped from it's normal position, without breaking valves (a chance) and this after many miles, it's unbelievable

so it can be usefull to inspect valve train (see page 150 of the repair manual you can download there : http://lekorbo.free.fr/mz/manual/) you will find there how to check the valves timing

[stephendacosta]

Double check the carburetor. I have never had one even burp spraying into the intake manifold. The mixture is very sensitive.
If you have two 125's, swap a running bikes carb to be sure.--Steve

[DAVID THOMPSON]

the rt125 has the most sensitive carb on any bike i have owned

when starting mine it refuses to start if i apply any throttle opening when cranking..
when it starts i go to half choke and let it warm up
its a learning experience with each 1

dave