ETZ 250 erratic running

[Cerberus73]

I changed the brake master cylinder on my ETZ earlier, to go with a freshly rebuild calliper, and when i went to take the bike for a run to see if all was well, and enjoy some nice sunny weather..

the bike would start but conk out, wouldn't rev, and after much head scratching i decided to check the coil 5ohm ish on low power side, and 13.6k ohm om the high power side, so seemed ok.. i then cleaned carb, stripped, cleaned and back on the bike. she's running but when i had her out for a shakedown, she goes to 5k rpm in say 1st o9r 2nd, and then feels like she's bogging down, hesitation. then all goes fine, no gear can i get her past 6k rpm which i know is pretty much it for a 2 stroke mz rpm wise. but the weird sensation at 5k rpm in 1st and second and the lacklustre performance from a standstill is weird, she was running great till i changed the brake cylinder.. any suggestions welcome, as I'm losing faith in this bike, its seems to be one thing after another i will adjust the oil pump tomorrow and check the points/condenser and alternator power output. as i noticed the charging light coming back on at anything under 2k rpm.. where before she was ok at tick over.

[DAVID THOMPSON]

in the work you may have done something to the electrical wires on the right hand side of the handle bars
or pulled something loose in the headlamp or wire loom
or under the gas tank if it was off
maybe one of the ground wires is loose at points where it attaches to the frame
also the bearings in the headstock make a poor ground return sometimes
a wire from the handlebars to the frame can some time sort a lot of trouble out of a system

the key switch could stand an inspection also
dave

[MichaelTorre]

What is on the handle bars of that machine that power has to go through ?
M-

[Cerberus73]

front brake light switch, switches for horn, headlight main and dip, headlight "flash" to other drivers., and indicators.. ignition switch, and the headlamp itself contains all of the front end wiring behind the reflector bowl. I've gone through the wiring, switches etc. all fine. made sure earths are good. same under seat. also drained tank, filtered all fuel, cleaned the fuel tap filter meshes out. stripped carb, cleaned it all.

the only thing i can think, is after all that it ran ok, but still odd glitch, and last night it started behaving terribly again, had to push it back to my garage as it conked out and wouldn't start or idle properly after it had warmed up. so its got me thinking its the coil breaking down when bike is hot. there was also a weird smell.. couldn't quite put finger on it or where from. I've ordered a new coil, and am going to strip and rebuild carb, set float height etc. i know the fuel tank is clean and the fuel itself is clean. the coil shows ok ish when tested stationary off the bike but i know they can play up when hot. also when fitting the brake light switch i had the ignition on but the bike not running for about 5 mins or so to check the switch was functional.. i know that can make a coil pop.. i wasn't thinking!

[Eric Frith]

I found that on my ETZ125 the only way I got it to run right was to fit electronic ignition ( I kept the original charging circuit) for about £100 you get the coils an' everything.

[Cerberus73]

ah i have one to fit eric, but don't intend doing it till winter, when i will rebuild the engine and carb (the frame etc is mint) I've already fitted a electronic voltage regulator, i have a kit that i got from burwins basically the powerdynamo without the new rotor etc cost 95 quid or thereabouts. it isn't the old kit they used to sell with there own name on it.

[MichaelTorre]

do you have access to a digital voltmeter?
And do you know how to do a voltage drop test on a circuit? Regards
M-

[Lone-Wolf]

Wotcha.

Mine did something similar - in the end it was the fuel tap occasionally blocking up. Luckily that's an easy fix.

[Cerberus73]

yeah I've a multimeter and can do all the usual checks on bikes. I've also cleaned out the tank lone wolf, and the tap was stripped and cleaned as well. and fresh fuel put in. i also went and decoked the exhaust from front to back.. lot of crap came out of there.. thick, black and sludgy.. so someone was over oiling it i thinks. i will strip the carb again as i have a new gasket to fit to the float bowl. old ones a bit shitty looking. will clean it out once again at same time i fit the new coil i have coming.

[MichaelTorre]

The voltage drop test is where you have a digital multi meter straddling an electrical connection that is live.

If your meter shows anything more than one tenth of a volt for a low power circuit such as a coil, light bulb etc,
then the meter is providing a pathway for current that the bad connection will not allow.

If the connection is bad and the current is not flowing properly, you provide an alternative path,
and the meter will indicate how much current is bypassing the connection.

heavy drain circuits are allowed almost .5 volt as an acceptable drop, but smaller circuits are not allowed more then two tenths , (0.2) volt drop.

Regards
M-

[DAVID THOMPSON]

the above comment explains why i hard soldered the voltage reg into the wire harness on my 2002 MZ rt 125
i could not get a good connection with connector plugs

yes its hard to remove if you need it disconnected
but very effective at making the problem go away
dave

[Cerberus73]

well the saga continues.. after fitting a new coil, the bike is still running like a bag of rusty spanners. its starting to get to me now. so i forked out for a new BVF 30N2 carb from MZ parts bristol on ebay.. carb turns up, i check float height, made sure all the jets were clear by blowing some compressed air down all the openings and channels. fitted the carb to my bike.

Now before i fitted carb, i fully charged the battery overnight, cleaned the points, checked the timing. and yet again checked the wiring and cables.. just to rule out as much as i could. the bike started no problem after a couple of kicks, but started to rev out.. we are talking 7k+ rpm and no amount of setting the air and throttle stop screws on the carb can get it to settle down, i have to turn the ignition off as I'm afraid the bike will have a blow up if left to rev out like that while I'm messing about with the carb.

Now when i was inspecting the carb, i did notice the air screw was a little "off" as in the thread had been tapped a little out of true from the factory. and on closer inspection i noticed the pointed end of the air screw would not seat into the hole at the bottom of the thread where its meant to sit into. and was off by about 1mm to the right as it had marked the body of the carb leaving a tell tale dimple. i am guessing this is the problem with the carb and i should return it for a refund or replacement? i will have a further look at it tomorrow as i didn't have time to spend on it today. also the carb didn't seem to be a genuine BVF.. but some sort of clone, being marked wm motor or something like that

at least i know it will rev now.. with the old carb it got to 4-5k rpm and started to jerk, splutter, misfire then die. shame this carb is just as bad for other reasons.. if anyone knows the stock setting for needle clip, the throttle stop and air screw for a BVF 30N2-5 id be grateful, the haynes and mz manual says 2-2.5 turns out for air screw but has nothing for the throttle stop.

[Diligaffer]

Got a similar problem with my 1989 MZ 251 - revs uncontrollably go past 6K. Bike starts easily - often after first kick but as soon as I disengage the choke revs go out of control.
Tried to change the carb settings when bike is running but it doesn't do anything at all (I just got a brand new carb - original BING 84 from Ost2rad.de, new intake hose, air filter appears to be fine and battery is fully charged).
Engaging choke around halfway makes rev go down and then she idles around 1K or slightly below that and ticks over nicely. I tried opening the throttle to see what happens but it just makes induction noise for few moments and revs very very slowly climb up.
Spark plug colour is black - so it runs rich...no surprise here thou as it was running on choke. I just don't want it to keep running around 6k as it sounds like its gonna disintegrate.
Any ideas what might be the problem?

[Cerberus73]

Mines was different engaging the choke didn't do nothing.. i ended up sending the carb back as it had a miss drilled air scew that wouldn't seat properly so same effect as a fully screwed out carb. but since yours is slowing down when you engage choke (richening the mix as you said) it settles down.. so to me that points to it either needing the air mix screwed down so it richness out.. as the revving points to it running very lean. so its either a problem with the air adjustment screw.. or its sucking in air from either the air filter sealing rubber.. or the carb to cylinder manifold.. or somewhere else like if you removed the oem air filter or stuck on pod filters without rejecting or setting the carb up for that setup.