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My CX has that too Derek! Starts right up if within a week, otherwise a considerble amount of cranking until fire.
Just an update.
After re-assembling the engine, the putting the contactless ignition on i found it still ran backwards.
Then I realised that it seems to run backwards at a perfect 22 degrees just as forwards. I find that the rotor trigger has two magnets at around 45 degrees! Obviously when kickback occurs, the other magnet allows it to run backwards. For now I replaced with contact breakers and it has fixed the problem seemingly. It does kick back, but it doesn’t ‘support itself’ and continue to run in reverse.
I guess case closed.
Have run at 1.5m btc but still been an issue.
I have however measured the stroke to be 66mm on the ‘suspect’ crank.
I’ll be tearing down the engine tomorrow and removing the suspect crank and replacing with one I’ve recently had reconditioned by Burwins.I have tested on both the original points system, the polish ‘Zaplon’ and currently on a hungarian ignition. All three gives the same result. All three use different cams and triggers.
Even more interestingly Peter, Is that the Luxus models of the 250/251 and the non-luxus (non injected oil) have the same size main jet according to the factory manual! Or at least, no information regarding any difference between the two are mentioned.
That said. I never did touch my jet. If i’m on 130, i’ve been on 130 for 20k miles 🙂 It’s what? 2% less fuel?
30:1/33:1 doesn’t matter. When my tank gets to reserve I chuck a pint of 2t oil.
I use cheapest/bulk buying mineral 2t oil and don’t have an issue. Have amassed 40k miles on one of my mz’s.
Just to update on this.
I marked TDC with tipex on the rotor with a static mark on the generator.
And with a timing gun with an offset of 22degrees programmed into it, I was able to adjust the carrier plate and set the timing thusly.
I have just had a thought regarding the re-built crank that I had spare that I installed in place of broken crank. I wonder if the lobe key is not quite correct..
I will be setting up a timing disc tonight and working it out that way.
When in constant motorway use I normally fill bike to certain level dependant on price and divide the litres by 0.033 and just pour in how many ML the output of the calculation gives, after the bike has been filled of petrol.
When my riding is around town I only re-fuel when bike goes into reserve normally put half a tank of fuel in, then empty the 500ml bottle of oil (I use the cheapest mineral I can get in bulk) that I keep with me and then carry on re-fuelling after that has emptied into the tank.
Interestingly, I’ve never really shaken the bike to agitate mixing. Not had a problem with over-heating (due to lack of concentration of oil after fill up) nor had pure oil coming out of the tap.
And I’ve done 10,000 miles on my 250 MZ in the past 6 months..!
Thanks for all the replies guys, I get the picture, not good! Anyway I’ve decided to sell it now, or at least the wife has decided I’ve to sell it! Its a great bike, everything else has been done on it, if you want to take a look its just been listed on ebay. Now I’m going to go and sulk in the corner……
RobYes thanks guy, I guess i knew it was one of those problems you can’t ignore.Time to talk nicely to the wife and get to the bank before she does!
I have experienced exactly the same thing,except I came off.
The cause was not the engine,but the rear brake locking on.
I was descending a steep hill,in the wet,and had to brake sharply.The rear wheel locked up and despite releasing the brake,stayed locked and I slithered sideways into the edge of the road,did a textbook “highside”and ended up on my arse.
Investigation found that the extrusion under the engine [where the footrest bar is bolted] had cracked at the weld allowing the footrest bar to flex up and down nearly an inch.This combined with me recently adjusting the brake to give about half an inch of travel,and the greasy road,was enough to keep the wheel locked.
Another thing worth checking is that the brake linings are not too worn.I have not had this on a MZ but on another bike,the brake shoes went “over the cam”and locked the wheel.This is caused by the brake shoes moving too far and the servo effect on the leading edge keeps the brake on.
Hope this helps.Talking MZs at various rallies,I have heard of two cases of the clutch drum coming loose.One from the bloke it happened to,the other from someone who knew someone.It seems to be fairly rare,and my guess is its cause is incorrect assembly and/or inadequate tightening.
A new clutch inner should solve it,I think it is the pressure plate that you need,the tapered inner is part of it if memory serves,[its been about two years since I last stripped my clutch].Both the MZ shop and Ost2Rad have them at £46 and 40 euros.
Best of luck with it.
