ETZ 251 mis-firing after 40 minutes riding.

[Blurredman]

Hiya guys!!

I like to use my MZ for work, but I find that lately, it works fine for initial half an hour, but around the 40 minutes mark of riding, the bike stutters and looses power and keeps hopping (if at speed i can keep it up until it somewhat goes away)- I have a volt display the normal 13.8 with lights on, and the ignition lights don't turn off with it loses power, so I'm thinking it could be the coil?

I've tried another voltage regulator, and i've measured the resistence in the diode plate and they're all equal.. Interestingly this seems to have just started happening as even with my charging issues I have been having, I didn't get misfiring like this before... Coil??

Any input well appreciated.

[DAVID THOMPSON]

are you still using old time point and coil system
on them some times the dwell has the coil on for a long duty cycle which makes the coil too hot
because the coil is on to much

[Blurredman]

I am using an electronic ignition that does turn off power to the coil after 20 seconds of innactivity.

[therealche]

I would change the coil. Sounds like it is degrading as it warms up

[Blurredman]

Thanks David for your pms.. they were interesting.



TheRealAche- That's what I thought.. Does anyone know the resistenciess???

I've measured my orange mz and the coil is measuring 13.25k ohms on both terminals to the cap, and 3k between eachother.

The one on the problem bike is measuring 8k on one terminal and something like 10k and rising on the other..


What are the specs??? I can't find anything on the internet..!

[therealche]

To be honest with coils I just tend to swap with a known good coil. I have had coils that work perfectly when cold, then when they warm up in use they fail. Even had this happen with new coils.

[DAVID THOMPSON]

some coils have a problem with points dwell if the system turns the coil on too soon before it is time for the spark to happen..

then the coil over heats from being on too long
there are ways that some electronic units control this on time but
i have not seen any articles about how they work
a friend i knew a long time ago would put in a ballast resistor of a slightly bigger ohm value and by cutting back
on the current flow he cut the over heating down

dave

[Blurredman]

I have purchased a new MZ coil... Fingers crossed.. For a £100 bike that I never intended to invest in, i've put a lot of money into it actually..

New clutch cover, kickstarter lever, coil, electronic ignition, battery, handlebar controls, carburettor jets, rebuild forks, new rear tyre etc etc Don't be tempted by cheap off the road bikes


Also, it might be the possibility of why the bike uses more voltage at idle, with a coil that promotes a big resistence,

[Blurredman]

So I'm really pulling my hair out now.

I got a new coil, And the bike misfires quite noticeably and doesn't hold an idle very well. Turning the lights on kills the bike. Total disappointment.


I'm going to be leaving this heap in a ditch I think as it has thoroughly pissed me off since I first got it. I'm dead serious. Problem child it certainly is..



What else can I look at? For a start it doesn't idle with the lights on (drains battery) which isn't too much of an issue if it remained my day bike but the fact that it cuts out is just too much. What else is there to look at? I will be swapping my coil and my diode plates from my working MZ next. Perhaps tomorrow I will look into it. Though i'd much rather kick it over.

[rodge70]

hi,is the ignition a cdi and is it ac or 12volt dc powered? and what triggers it as i assume you have dispensed with points,condenser etc,cheers

[DAVID THOMPSON]

with older bikes i had a problem with the system keeping UP with demand

the point and coil system on both my Harley hummer 165 and my BMW r27 250
was the generator was a pain they could be new and still not work correct always low output

so i had a 6v battery for the bike and a 6 volt car battery in the saddle bag for the points and coil circuit
the the BMW R 27 was a great bike but every one of them i had would not keep the battery charged

every bike i own gets an extra battery even my MZ rt125 has a backup on the starting circuit
for cold weather

[Blurredman]

Thanks for getting back guys. Last night I thought I resolved the issue.. It idled, with the lights and indicators on too. It was running around 10.5 volts but it was stable.

I decided to test ride it today including to charge the battery. Well I've been out on it and it runs fine though every time you stop at lifhts it gives maybe two misses and then promptly stalls with a little misfire. I've done some experiment and it does this lights on or off and with lights on it is around 11.5 volts and it doesn't falter when it is missing.

It pulls well otherwise and as long as I keep the RPN up a bit I can prevent or even recover from impending stall.. I will be cleaning the carburettor out focusing on the idle circuit in a last hope.

Yes it is an aftermarket cdi unit. Though it did the stalling before I bought it. I thought it would resolve it. New coil and a known working diode plate set...



I

[Blurredman]

Nope... Cleaned carb. Went for tests. As soon as I turned the lights on and dies

[DAVID THOMPSON]

my 4 stroke rt125 idles at 1800 udm (rpm) are you trying to idle it toooo slow

being it fires every time it is at tdc 1200 to 1400 should work
but less than 1000 is a bit low

also a slow idle makes the battery work harder

[rodge70]

Yes it is an aftermarket cdi unit

do you know if ac or dc powered,usualy ac ones are larger than dc powered units iirc and run on a high voltage from stator,could be worth checking ac output from the off then when mis-fire happens