Intro and question

Forums Technical Two Stroke: Hints and Tips Intro and question

Viewing 6 reply threads
  • Author
    • #13326
      ‘AAA Dummy

      Hi Everyone

      I’ve just this week taken delivery of a Blue 1976 TS 250 4 speed. I promise I’ll put some pics up once I’ve worked out how to! I’m in Durham so if anyone else is nearby ….. Hi ……… and probably help!

      So….. to my question……When I picked the bike up it started and burbled and ticked over fine on the sellers drive.

      I brought it home in a van, unloaded, started it and it seemed fine and I put it to bed. Next day, first ride did not go well.


      1 it started and ticked over ok but did need some throttle to keep it stable which it hadn’t when I picked it up
      2 into gear, clutch out, off the drive, all is good.
      3 up through the village, left at the top, and finally get into 4th 30mph max).
      4 approaching a traffic calming chicane, looking for 3rd, not easily achieved but finally in, put down to first time nerves
      5 Down a gentle slope to a tight left corner……
      6 clutch in, looking for second, no way, throttle on, just revs, no power, false neutral? clutch back in, looking for 2nd, still no sign, coast to a stop about 20 yards after the corner.
      7 clutch still in as I wasn’t sure it was in true neutral.
      8 stopped
      9 …….. now it gets nasty! ……..engine revs start to rise
      10 10 secs later, engine screaming – I mean SCREAMING
      11, clutch still in, because if it’s in gear and I let go it will skyrocket
      12 SCREAMING continues
      13 fuel tap off….. continues
      14 pulled spark plug cap off….. continues (that was what worried me the most that it was dieseling)
      15 now out of my comfort zone…. I have a SCREAMING bike and no connection to fuel or spark but going berserk
      16 I’ve had it about 18 hours and think…… I don’t need this so let the clutch out…….. it just SCREAMS
      17…. about 150-180 seconds later it finally runs out of steam, stops and everything is quiet
      18 wait until things have cooled down….. have a poke around….. reconnect the plug cap and fuel line, kick start…..running, not screaming, but not stable, won’t tick over, needs some throttle to keep it running
      19, into gear, off we go
      20, behaves ok with some clutch slip
      21, next corner, yes, another left, but uphill, not steep, behaves ok
      22 straight road, about a half mile, all good, approach next corner, a downhill left, stalls
      23 restarts straight away, off we go
      24 Final left approaches, down into 2nd, no 2nd gear, false neutral again, drift around the corner with clutch in, 20 yards coasting and trying to find a gear, any gear, no gear available, pull in
      25, revs start building, and building and building and finally it’s SCREAMING again.
      26 repeat of steps 13, 14, 15
      27 Finally cuts out so by now I am about 200 yards from home so just wheel it home, embarrassed and a tad p**** off

      What I found when I finally got home and had a cuppa was two weird things:
      a the exhaust Collar had unwound itself and the exhaust was no longer attached to the head
      b There was oil (fresh) all over the left side of the engine. On closer inspection the oil level inspection bolt was missing so oil was peeing all over the engine whenever the bike was tipped to the left (my left corners)

      Today, I replaced the bolt and started up and still not right.

      So… my question really is, anyone any ideas?

    • #13328
      Andrew Staley

      Hi Mike, you don’t say if this is your first experience with an MZ but if it is, I can tell you that most MZ ‘rides out’ are happily not as mechanically exciting as you have described.

      I am not sure whether you should be looking for a mechanical reason or should be phoning a priest to perform an excorsism!

      Anyway a few thoughts:
      – Contact the seller – may be able to give you a clue – take a couple of burly mates and suggest having your money back!

      – Re the gear change problem, there can be many reasons for this which involve grubbing about with the gearbox internals but firstly check that the detent ball and spring are still in place in the plug under the engine.
      If the level screw was missing and oil was leaking over the motor then it may indicate that the oil has been recently changed and its easy to remove the ‘wrong’ plug and lose the ball and spring in the old oil.
      I have had 2 MZs with the ball and spring missing.

      Re the screaming, remove the plug and check that the ignition switch actually turns the spark on and off.
      If it carries on running even without the plug cap on then there must be a hot spot within the combustion chamber – is it the plug electrode overheating because the mixture is very lean or there’s a build up of carbon on the head or even a home made gasket with raggy edges.
      Is the carb slide very worn so air is leaking past to cause lean running?
      Check the throttle and choke cable are not badly routed, trapped, crimped or just too short when you turn the bars from lock to lock.
      If the motor is screaming, it’s obviously getting fuel and air so look at the carb end of the choke mechanism to check the rubber seal is in place and not leaking fuel through, check the carb is a tight fit in the manifold and the manifold is properly fitted to the barrel.
      Check the carb throttle slide return spring is doing its job.
      Does the carb look new – is it a cheap Chinese copy, many of which work fine but some don’t?

      Re the loose exhaust, that might indicate that it was not put together tightly or screwed in without the sealing gasket ring.
      Hopefully it’s not because the exhaust port threads are sha**ed!

      Apart from that I’m fresh out of ideas but I’m new-ish to MZs so I imagine our more experienced MZ-ers will be able to put you right.

      If all fails, I have a nice crisp £10 note waiting and I’ll take the pain away – just down the valley in the N Pennines!!


      • #13334
        ‘AAA Dummy

        Hi Andrew

        Not a great introduction to the ways of the MZ I have to agree.

        I’ve had a few whatsapp conversations with the seller, but I don’t really want to keep going back to him as In all honesty the bike was there, as described and ran well on tickover on his drive for as long as it wanted quite happily.

        As for the honestly aspect, I felt he was an honest guy, had owned the bike for quite a few years and knew everything about, answered all my questions etc so cash was exchanged in good faith.

        So, I guess I have two issues to deal with, the first being the carburation and then once that is sorted the gearbox issues, although I’ve a feeling one is connected to the other. If my drive shaft was spinning at red line speeds I’m not sure as a little gear cog I’d like to stick my splines in there!

        Thanks for your suggestions and ideas. Definiely food for thought. I’ve a feeling the carb might be a cheap chinese replacement as it looks a lot younger than the alloy around it.

        The fit to the airbox side is tight but on checking the engine intake side it is loose, despite the clamp being fully tightened, I might put some gaffer tape on as a temp measure to see if that can be ruled out.

        When I removed it the plug was very light in colour so was def running lean and that would ties in with the symptoms.

        I’ll check that spark suggestion when the ignition is turned off and just pray that it isn’t live all the time, although I have kicked it over with the key to off and it doesn’t fire up.

        The exhaust collar, I’ve removed, cleaned up with some brake cleaner and wire brush and the threads looked ok, it went back together and seemed to tighten up sufficiently but I need to double check with a c spanner.

        As for your tenner….. I’ll pay you a tenner to come up and fix it for me ha ha!

        Thanks for your help and useful ideas, I’ll keep you posted.


    • #13367
      Greg Moore

      Hello Mike
      When you first started the bike at home to go for your ride you said the tick over was a bit unstable, did you by any chance turn in the tick over screw to increase it? If you did this could be the cause of your problem; if the slide is slightly too high some MZs can tick over reliably, but if the throttle is blipped the revs stay high and don’t come down when the throttle is shut. I believe this is caused by the increased revs drawing more air under the slide, increasing but weakening the pilot mixture, a weak mixture will cause the engine to race and a cycle begins; more air more revs, more revs more air…


    • #13382
      ‘AAA Dummy

      Hi Greg

      Thanks for that, I certainly did, I twiddled everything!

      Yesterday I untwiddled and reset everything to factory settings, also installing a rubber O ring between the carb and the inlet manifold as that too was slack and obviously would have been drawing air in. Since restarting it it does tick over much better but still isn’t consistent, it still stays a little too high when revved – so I’ll have another look at the tickover screw, and, it tends to die off once it starts warming up, any ideas on that one?

    • #13394
      William Sweeting

      Had sort of similar issues with a 250.
      Would either rev far too high or not at all.
      Incorrect sized pilot jet. one size bigger cured.
      Also if the carb is loose in any way between itself and manifold it will never run right. This needs rectified first. If unable to tighten it could be cheap S**t that is undersized and is fit only for the bin. No O ring required.
      See if you can borrow from somewhere an original BVF carb to see if it makes a difference. Doesn’t matter if its worn or not will simply prove where the issue is.

    • #13395
      ‘AAA Dummy

      I took it out for a 2nd ride yesterday and it was a lot better but still wanting to fade on no throttle. I didn’t mess about with any settings, I just wanted confirmation that my previous route (all 1 mile of it) wasn’t cursed, that it could and would drive forward without screaming, and that it wasn’t me imagining it all.

      I think the manifold is a Chinese one too hence the ill fitting issue, so I also put some thread tape on there to bulk it out and to back up the O ring……

      So far so good…. weather looks ok tomorrow so a bit further and see what happens………. Luckily I’m in the RAC so….. ‘ll keep you posted!


    • #13420
      ‘AAA Dummy

      It rained…. a lot! Ride deferred to a later date!

Viewing 6 reply threads
  • You must be logged in to reply to this topic.