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Good afternoon everybody!
As I’m sure everybody knows by now, MZ’s run on a petrol/oil mix of either 33:1 or 50:1. Given the improvements in oil quality since our beautiful machines were made, could a 33:1 bike be run on 50:1? (Or change from 25:1 to 33:1 on older IFA bikes/scooters?)
I’ve recently read a couple of articles in a classic bike magazine that this is possible.
Any thoughts anyone?
Kind regards, Neil
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Hi Neil,
As I understand it, the 250 motors went from 33:1 to 50:1 at the time the Supa5 was introduced. prior to that the main bearings were lubricated by gearbox oil so the mixture ratio was only concerned with lubricating the bigend, piston and small end. Don’t think the piston or big end were changed significantly but early motors had bronze bush small ends whereas the later motors had a needle roller bearing. It was this that supposedly allowed a weakening of the oil ratio. Other factors may have come into play, improvements in oil quality and possibly a marketing influence to make the bikes seem more modern in the Western world.
For what it is worth I have always run my ES250/2 on 50:1 even with a 4spd motor but this does have a needle roller small end. It has never seized or given me any problems related to fuel mixture – plenty of electrical problems though but I don’t think lack of oil was the cause!
The 125/150 motors went from 33:1 to 50:1 around the same time as the 250 motors as far as I recall but on what basis I don’t know.
However, in truth the difference is marginal in terms of cost and smoke reduction so I would tend to err on the side of caution over reducing the amount of oil in the earlier engines unless you know for sure the condition of your motor and what type of bearings it is using.
Peter
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A metered oil supply is supposedly more efficient and therefore economical than rough and ready premix, but my own ETZ oil pump runs much richer than the recommended premix ratio of 50:1. This seems to be the common experience; I have not heard of anyone who gets a leaner ratio, as one would expect.
Can anybody explain this?
Have any ETZ owners kept a record of their long term 2T usage? -
Good evening everybody!
Many thanks for your replies, I quite agree about only saving a marginal amount of money (I think you’d have to cover many, many miles to show any significant savings) and since the only way to see if it’s a needle roller bearing or brass bush is to strip the top end……rather pointless if everything’s running ok. I think I’ll leave everything as is.
Besides……a gentle haze from the exhaust drifting serenely across the countryside is rather traditional with a MZ!
Kind regards and many thanks, Neil
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I am really a MZ 4 stroke man (Rt125, Skorpion and 500R) but am now renovating a Jawa TS350 and hear the same discussion in the Jawa community. The oil in the fuel is the primary insurance against seizure. Why would anybody want to risk a low oil mixture ratio on the basis that the modern oil is better than oils of yesteryear? What is the driver to reduce the oil ratio? Cost? It’s peanuts. I would suggest the best ratio is the most oil that the engine will run happily on without affecting performance or reliability such as oiled plugs. Why tempt the possibility of seizure ? I don’t understand why anybody would want to take a risk. In any case the smell of a two stroke bike is something to be savoured, the smell of two strokes on the race circuits is one of those things like rain on a summer’s day, onions frying in the burger van, hawthorn blossom and the extract fan from your local Chinese take away that should be treasured !! As the club T Shirt says “I love the smell of two stroke in the morning” and as I read elsewhere “would you underfill your gearbox on the basis that modern oils are better than old oils”?
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It seems Matthew is one end of the arguement and I would agree that 33 or 30 to one is not the issue. When you start thinking about 40:1 then it is an issue. An arguement on the Jawa club site is that 40:1 was introduced as a reaction to emissions laws but it is a significant risk to the survival of the crankshaft bearings. Personally I feel a ratio of 33:1 using a branded two stroke oil is a sensible compromise. It won’t break the bank any you can reasonably expect good lubrication of the engine bottom end.
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Cycle magazine of February 1978 has a five page article on two stroke pre-mixes. I have it as a pdf, but don’t know how to ‘share’ same here. They test 15:1; 20:1; 30:1, and speak of 50:1.
Their ultimate sentence is, quote: –
“Less, in the context of pre-mix lubrication concentration isn’t more; it’s less. Just as logic always insisted.”I have a family member who ran a Husqvarna 360 chain saw for twenty odd years on forestry work on the most frugal of mixes. He even used used car oil to lube the chain. I had the job of servicing his saw when it died, and found the cage of the main ball bearings disintegrated, the small parts finding their way above the piston where before being ejected through the exhaust port, had hammered the piston top so much that instead of being flat topped, it was dished! New bearings and piston later, it lived to see many more days of work.
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When I originally opened this topic, I didn’t realise what a big can of East German worms I’d be opening (and I only enquired on behalf of a friend!)
For the record my old DDR machines run on 25:1 and I shall be continuing to run it on that mix, I think that modern 2t oils burn more completely than oils available in the 1950/60’s so they won’t smoke as much, although a nice faint haze from the exhaust is very evocative! And as I use Putoline strawberry scented oil you also get a faint but nice smell of strawberries.
Regards, Neil
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Something not to be overlooked and not mentioned so far in this debate is that changing the premix ratio also affects the fuel supply. Adding more oil weakens the mixture, reducing the oil ratio richens the mixture. MZ took this into account as follows: The 4spd TS250 uses a 140 main jet(33:1), the Supa5 1 135 main jet (50:1) and the ETZ250 (with oil pump) uses a 130 main jet (no oil in the fuel) in what was essentially the same 30mm BVF carb.
That should fan the flames of debate.
Peter
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Peter,
Surely the TS250 4speed runs on 50:1 petroil, as do the Supa5 and the early ETZ250 Standard model, even thought they all have different size main jets. I think the ETZ Standard and Luxus models both had a 130 jet even though one used prexix and the other did not. If this is correct, the changes in jet size were unrelated to the use of premix or its ratio. -
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?
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Hi everyone!
I seem to remember reading somewhere that ES125/150’s used a brass bush little end so needed a 33:1 mix but was changed to 50:1 as the newer TS’s used a needle bearing little end. Also did the 250 engines change in the way the main bearings were lubricated? (Lubricated by petrol/oil mix as apposed to the gearbox oil or visa versa)
Any thoughts/opinions anyone?
Regards, Neil
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