MZ/MuZ Riders

Can anyone help?
Recently acquired ETZ 125 1991 which was running. Had been sitting for months and minimal use for several years.
I have replaced the carb as it was very worn, points, condensor, cables, fuse box, clutch, primary drive, battery, kickstart quadrant gear and a new plug.
Passed its MOT and now will not start.
No spark from the plug. I tested the HT coil with a multi meter which seems ok.
Your advice much appreciated.
I bought it for my 17 yr old son so trying not to put him off bikes as he does need something reliable.

Welome newbie.


What's the voltage on the battery ?

Thanks for the Welcome, much appreciated.
The battery is new, Yuasa Motorcycle Battery 12V 5.5Ah 55A and output measured is 12.35V.
I was sorting out the carb idle, ran fine and then nothing. No spark.
I have had bikes for nearly 40 years, can do maintenance but this I am stuck.
Any ideas?

if bike has points some times the spring in the points goes weak or bad making it not fire

Thanks David for reply, I have replaced the points so wondering what next I could try.

Try a different spark plug..

I know it sounds stupid, but i can't count the amount of plugs which have pre-maturely gone.

Hi James!

You have replaced much, sounds like quite an overhaul. Maybe a poor connection somewhere, or corrosion, anyway, lack of electrical continuity. Mine sometimes has an issue in the fuse box (which you replaced).

With ignition switched ON and the contact breakers (= points) OPEN, check that you have voltage across them. And with the breakers CLOSED, that the coil gets current.

Pull the condenser connection off & see if it then sparks. And yes, try another plug, or just hold the HT cable a few mm from earth.

If still no luck, try another coil (any old 12V coil should do for a test).

Thanks Puffs for your reply.

Voltage across open points is ok and 11.4V across coil when points closed.

I have tested the battery with leads off = 12.2V. Its dropped from 12.35V overnight.
With ignition on = 11.83V
The coil disconnected is 11.2 ohms. It does jump around a bit
Coil to end of HT lead is 10800 ohms
Coil to spark plug cap = 11630 ohms

Spark plugs checked as well, ok.

Anything else I could check?

Puffs wrote:Hi James!

You have replaced much, sounds like quite an overhaul. Maybe a poor connection somewhere, or corrosion, anyway, lack of electrical continuity. Mine sometimes has an issue in the fuse box (which you replaced).

With ignition switched ON and the contact breakers (= points) OPEN, check that you have voltage across them. And with the breakers CLOSED, that the coil gets current.

Pull the condenser connection off & see if it then sparks. And yes, try another plug, or just hold the HT cable a few mm from earth.

If still no luck, try another coil (any old 12V coil should do for a test).

after all else ground the head on the motor to the battery minus
some where its not grounding the system correct

DAVID THOMPSON wrote:after all else ground the head on the motor to the battery minus
some where its not grounding the system correct

Hi David
Sorry I am being a bit dim but
Can you explain what you mean "ground the head on the motor to the battery minus"
Thank you

a wire from the head where the spark plug seats to minus on battery
i think the earth side of the wiring is not getting connected to every where it needs to be connected on the bike

An earthing issue of the engine is possible, and although not very likely (as you measured a proper voltage across the open points), it's worth a try. Is easy.

Did you pull the condenser off? That might have shorted.

I don't know what the resistivity of the primary coil should be. Around 11 Ohms is plausible, but it should be a stable value. Around 11kOhm for the secondary also sounds plausible. Nevertheless, this kind of ignition is very simple. If you have voltage/charging current across your coil, and your contact breakers work, and it doesn't leak across the condenser, and you have electrical continuity where it's required, there's only the coil left. See if you can find another one for a test.

Thanks Puffs, will try a new coil tomorrow and let you know.

Puffs wrote:An earthing issue of the engine is possible, and although not very likely (as you measured a proper voltage across the open points), it's worth a try. Is easy.

Did you pull the condenser off? That might have shorted.

I don't know what the resistivity of the primary coil should be. Around 11 Ohms is plausible, but it should be a stable value. Around 11kOhm for the secondary also sounds plausible. Nevertheless, this kind of ignition is very simple. If you have voltage/charging current across your coil, and your contact breakers work, and it doesn't leak across the condenser, and you have electrical continuity where it's required, there's only the coil left. See if you can find another one for a test.

OK, new coil and no change.
Can anyone explain the process how a bike produces a spark from when you kick it over,
I did change the clutch plates, primary drive and kickstart gear on the other side, would that have had any effect.

The bike ran well, up and down the road then once home it just refused to start.
Any advice appreciated.

Puffs wrote:An earthing issue of the engine is possible, and although not very likely (as you measured a proper voltage across the open points), it's worth a try. Is easy.

Did you pull the condenser off? That might have shorted.

I don't know what the resistivity of the primary coil should be. Around 11 Ohms is plausible, but it should be a stable value. Around 11kOhm for the secondary also sounds plausible. Nevertheless, this kind of ignition is very simple. If you have voltage/charging current across your coil, and your contact breakers work, and it doesn't leak across the condenser, and you have electrical continuity where it's required, there's only the coil left. See if you can find another one for a test.

Try a hotwire. IE a wire direct from the battery to the coil positive terminal. Make sure the HT lead is well connected to both the coil and the spark plug.