mz 125 sm, several problems

[biohazzardz]

i just picked up my first mz, its a 125 sm and it is currently very far from its original factory condition

several things have been changed/removed
radiator hose has been changed to a braided line
airbox was removed
battery has moved
electrical and components have been moved around
carb was changed to a flat side carb(changed back to the original vm24 because i couldn't go past half throttle without the engine dieing)

as of right now it has several problems,
ocassional gear slip( it will slip back into the previous gear)
battery doesn't seem to get a charge, i can start and ride for a while(about 50 miles) then it won't start or will slowly die and stop firing the spark plug and the bike will misfire and die.

I'm new to the mz line of bikes and would greatly appreciate if anyone could help me fix this bike to get it in a usable condition.

[biohazzardz]

box of parts that came with the bike

[DAVID THOMPSON]

you have your work cut out for you
i hate it when a nice bike is owned by a chronic modifier

check the voltage regulator/rectifier unit mine died on day 2 yes at about 30 miles

also have suffered from a bad bunch of fuses over the years

see the relay 19 problem notes

and get the carb back to stock
and the air box and filter on it
the boys at the factory had this thing reliable and running strong
all the mods i have seen make it run slower use more fuel or just plane not run
there are 2 relays on this bike one is relay 19 it works with the side stand switch
and there is an other some models its back by the tail lamp and others its under the gas tank

easy way to find it is get a helper with good hearing and turn on the key while listening
for the clicks as it goes on and off
these go bad as the contacts are to small for the load they run through them
and when there bad they cause all kinds of stuff to not work
they can be replaced by a auto relay used in cars to switch extra lamps
questions ask
nice daily driver
dave

[biohazzardz]

do youthink having a k&n air filter on the stock carb would affect it much, since the previous owner welded steel plate where the air box should go to hold the battery

[DAVID THOMPSON]

you can adjust the filter but finding things to get the carb adjusted will be hard ..
if the air-box is still available i would torch and grind the frame back to stock

i only change handle bars or the seat so i can get my feet on the ground.

i will confess to modifying ssb cb radios to 10 meters for ham radio use
but i try to leave the bikes stock
dave

[biohazzardz]

changed the main jet on the vm24 to cope with the filter change and seems to be running fine, the relay 19 seems to be covered in a turquoise corrosion on 2 of its connections. I'm going to look for a replacement tomorrow when stores are open.

so a bad voltage reg could be the cause of the battery somewhat not charging?

[DAVID THOMPSON]

the battery may be toasted

i will look at the size in my rt125 its bigger than stock but has to be removed to check the water
dave

[biohazzardz]

i actually replaced the battery after it first died on me, i had a spare 12v 9ah battery still brand new in box

[DAVID THOMPSON]

9ah is a bit of a wimp i run 14 ah and it starts but you got to play with things ..like the plastic side cover
gets modified but for a good useful cause
i never saw a bike that did not need a bigger battery
dave

[biohazzardz]

ill have to try that out, i just want this mz running, its a good looking and fun bike for around town use... until the battery runs out on me

[XCalsteRX]

Hello Bio, my RT hasn't been starting off the button recently, thought it was a problem with the battery turned out it wasn't at all after charging and checking the voltage with a meter. I've just now adjusted the choke cable near the handle bar almost fully out, with this done I pulled the choke to fully on, took the charger off the bike and then turned it on, pressed the button and fired right up! So I'd recommend you to try this also, a tip..you may have to twist the throttle fully open whilst pressing the starter button, then switch the throttle off whilst still holding the starter button and it should crank harder and hopefully turn the engine over! I'll keep you updated if it works in the morning to after being off charge for 12 hours.

[DAVID THOMPSON]

mine will not start from cold with any throttle at all the slide has to be shut
when warm it refuses to start if any throttle is applied..
probably varies from bike to bike

and mine hates gas with ethanol in it

mine is still setting on the parking pad out front so i will see how it goes tuesday
things just do not seem to get done in a timely manner around here
need to put the bike away and the mower
yuk its almost January
Dave

[biohazzardz]

its not that it doesn't start, its that the battery literally slowly dies as i ride(hooked a small voltage reg as i was riding) its to the point where i can get it running with a bump start and it will idle with 7volts but if i try to pass 2000 rpm it doensnt have the power to the ignition coil and the bike flat out dies.

[michael]

there are two possibilities :
- the connection between the red wire coming from the regulator/rectifier is wrong, clean it
- the regulator/rectifier is out of order or the connexions are wrong, first clean connexions

to find help you can download the repair manual for SM there : http://www.sendspace.com/file/q9pgh0 (notice entretien MZ 125 SM SX.pdf (7.58MB))

you can download the 2005 RT shematic diagram there : http://imagik.fr/view-rl/74762, the same for SM exept there is not counter on SM
the colors on the picture are not true, I done them to find easily where each wire is going, the real colors are written ... for example Rt/Sw mean Rot /Shwartz (= red/black) it's in German (sorry), and explanations in French (sorry too)

you'll find explanations about regulator/rectifier on page 125

sorry for my bad english I'm French