So the TS 250 has the 'Nicest' Engine but why?

[Ian Richards]

I own a ETZ 250 and, like many other members, I am always looking for ways to ‘improve’ it. This has been particularly true in the past 10 months, with so many other activities curtailed by Covid, I have had an unprecedented amout of free time to fill.
It seems to be a widely held opinion that the TS 250 represents some sort of ‘sweet spot’ for MZ two strokes, with adequate power, delivered over a wide rev range, and reasonable fuel consumption. I had hoped to experience this for myself in 2020 but we all know what happened there. In contrast the ETZ 250 is generally held to be too peaky, thirsty and lacking in torque. That I would say is my opinion though my two stroke benchmarks are BSAs and Villers units of the 1960s, and last experienced in that era as well.
So, what’s the problem with the ETZ? A comparison of the powwr curves given in the workshop manuals suggests that the ETZ actually has more of everything at the same rpm than the TS though it does admitedly use more fuel doing it. The power curves don’t tell the full story however as they are for full load, also known as wide open throttle (WOT). It is also widely held of course, that this is the only way to ride an ETZ. Neither do the power curves go down below 3000 rpm, which is where owners would most like a bit more urge. Is it possible that the TS feels ‘nicer’ not because it has more low-end torque but because less happens when it is revved harder? I shall wait to be corrected.

Now as to the ‘why’. Again it seem to be widely held that the reason for the superiority of the TS is to do with the porting, particularly the exhaust port, which opens a few mm earlier in the ETZ engine. This would seem to make sense as extending the exhaust timing is carried out in order to to move peak power to higher revs; a pointless exercise it would appear, as the exhaust system is designed to prevent this (or so we are told).
But, if all this is true, what about the late model 251s? These seem to have the top of the exhaust port at almost the same height as the TS but I have never heard anyone say that the the 251 is ‘almost as nice’ as the TS. In fact I have nver seen much written about the 251 at all; comparisons always seem to be between the TS and the ETZ. Strange, they made plenty of them.
Now to another piece of evidence, that excellent article written more than 10 years ago by Derek Pickard, with which many of you will be familiar. Derek fitted a 301 top end to his ETZ, thus picking up not only the benefits of an extra 50cc and also the later exhaust opening of the 251/301s cf the ETZ. Not only that but he notched the piston crown in order to reduce the ‘exhaust lead’, again bring the porting closer to the that of the TS. At the end of the article, the disappointment at the outcome is very obvious; although it is all subjective, his conclusion was that it still felt pretty much as it did before. There seemed to be a bit more grunt at slightly lower revs but it was still felt like an ETZ 250.
So what can we learn from all this? Are all the TSs better than all the ETZs, with the 251/301s somwhere in between or is there more variability than this? Two strokes are known to be sensitive to small changes (this I do believe) and surely IFA made enough ETZs to know if they could be improved by a minor change to the barrel. Or is there something else that I haven’t thought of?
If someone reading this has a spare TS barrel and head I would be delighted to fit it to my ETZ. I wouldn’t be the first I know, but I have yet to come across any first-hand account of what difference it made.
If I am talking a load of tosh, I am sure someone who has ridden all sorts of MZs will let me know. In the meantime, I think I will leave my engine as it is (standard apart from a Mikuni carb and VAPE electronic ignition). With luck, life will have returned to normal and I’ll spend time riding the bike before I have a chance to start Project Reed Valve!
Ian

[Brian]

Hi Ian

I have a TS250/1, Supa5, and only have experience of a short ride on a ETZ250. Esentially I found that the TS250/1 pulls sensibly from around 3,000rpm whilst the ETZ needs around 3,500 to give the same sort of pull. The difference was nowhere near what I was expecting from reading the same sort of things you have. Definately recommed trying a TS before you make any decision.
Just so you know the cylinders are more different than just the porting. Stud size and spacing is different, crankcases are different with the start of the transfer ports being bigger in the ETZ engine. The cylinder is a different height due to the revised crankcase. It’s possible to fit a TS cylinder to an ETZ but requires a 10mm (I think) spacer under the cylinder scalloped out to merge the ETZ crancase transfer area to the TS cylinder, the cylinder studs of the correct size and spacing need fitting to the spacer. I thought I had a copy of the article I saw on this conversion but I can’t see it just now, if I find it I will let you know.
I think they modded the ETZ to match the characteristics of the then current Japanese bikes. Whilst Wilf wanted to stay with a cheap and cheerful commuter bike the Factory deceided to challenge the Japanese, so it got a peakier engine, oil pump, disk brake, 18 inch rear wheel and more current styling. Plus of course an increased price which definately didn’t please Wilf. Was this the correct decision? Answers on a postcard please.

Brian

[Ian Richards]

Thanks for this, Brian. I had assumed that the architecture of the TS engine changed when the horizontally-finned head was introduced. I can now see why quite complicated modifications to the ETZ barrel are sometimes recommended rather than a barrel swap.
I shall certainly follow your advice to proceed with caution as I am generally very pleased with the bike as it is and don’t want to spoil it.

Now, I may have got this wrong as well but I understood that the ETZs made for the domestic market were substantially less powerful than the model we are familiar with. Was this achieved with milder porting or simply by a restrictive, I wonder?
Ian

[Derek Reynolds]

I can’t add anything to this discourse, but thank the OP for an interesting read. I have a small book by Rob Carrick & John Wood entitled ‘Villiers Singles Improvements Handbook’ and the technicalities of tuning two strokes is a very complex subject. Pretty irrelevant to MZ discussion, but a great little book. The only tuning I ever did to my first bike, a Francis Barnett Plover, was put put petroil in the tank! Later had a 9E in a DOT trials, but did nothing to that engine.

[Brian]

Ian

Don’t know about reduced power on early ETZ’s but they were offered with the option of drum front brake and premix ie no oil pump. I think this was to reduce the price differential between the ETZ and the TS for buyers, maybe to appease the likes of Wilf, but perhaps there wasn’t sufficient sales to encourage then to continue. I believe that the early disk brakes were imported Brembo, rather than the licenced copy they used later and the oil pump was from Mikuni in Japan so it could of just been economic/currency difficulties with importing stuff.
Oh I forgot to mention the 12V electrics on the ETZ changes/improvements.

Brian

[Peter Fielding]

Another benefit in my view of the earlier ETZ250s is the larger frame and 18″ wheels front & Back so you only need one spare inner tube. I don’t really like the ETZ250 power characteristics much either. I am told the porting on the 251 versions is milder but I cannot say I really noticed this when I have ridden one.

A few years ago I modified an ETZ250 by fitting a TS250 top end. This is a bit tricky as the stud spacing for the two is different and the ETZ barrel is longer needing a 15mm spacer to bridge the gap. But that does provide a means to sort out the stud spacing. It worked well enough for me to use the bike for a year or so including an E2E ride. Later the engine was fitted into a Trophy and sold with that bike.

However, by a curious quirk of fate it came back into my possession a couple of years ago and is currently fitted in an ETZ250 special I am working on.
It would in truth have been a lot easier to simply fit a TS250 motor into an ETZ250 chassis, they drop straight in, but at the time I wanted 12v electrics and the oil pump. On reflection I may very well fit a TS250 motor to my special with a Vape kit and accept the pain of premix.

Somewhere I have a drawing of the spacer, and its somewhere in the back numbers of MZ Rider – about 2009 I think.

I think the suggestion to try a Supa5 first is sensible, you may find you don’t really notice much difference enginewise. But you will probably notice the cramped riding position. My bike has a raised seat and dropped footrests to make it more comfortable.

[Ian Richards]

In addition to fitting the VM30 carburettor, I had three possible engine ‘improvements’ planned for my ETZ 250.
These were:
1. Increase the capacity to 300 cc or perhaps beyond
2. By one means or another, alter the porting to something near that of the TS
3. Fit a reed valve

Each of these modifications has attendant downsides, one of which is that the modification might not work as well as anticipated (perhaps that should be ‘hoped’). Another is that each of them is difficult or impossible to reverse, except by replacing the modified parts.

When I bought my MZ it was always intended to be an interesting and inexpensive bike that I could modify as I wished without worrying too much about originality. Unfortunately the supply of cheap secondhand parts has largely dried up and the Covid pandemic seems to have accelerated the trend towards these bikes becoming ‘classics’. I don’t need another one of those.
So what should I do? It rather looks as though I should throw a dust sheet over it until the spring and find something else to occupy my time.

Ian

[Brian]

Peter

Thanks for that I thought i’d seen it in a Real Classics article, no wonder I couldn’t find it. It’s Issue 174 July August 2008. I have a copy so if anyone wants a scan let me know.

Brian

[‘AAA Dummy]

Thanks, all interesting stuff guys. Did look to lower my footrests but gave up, so how did you arrange yours Peter.
Have been having great probs with motivation but the article on the 502 really perked me up. Really good piece specially at the end when the cockups are admitted. I make plenty. 🙂

• This reply was modified 3 years, 10 months ago by 'AAA Dummy.

[Matthew Nichols]

A bit late to the ‘partay’ I know but upon reading this topic I thought I’d outline my views.

As an owner of an ’90 etz251, and an ’87 etz250 (and also the new owner of a 250/2 trophy but that’s besides the point perhaps), I can say that I don’t really think too much of the ‘peaky’ performance people say they have.

When I bought my etz250 in 2012, I did have some trouble with the carburettor- it could have been my naivity or something ghostly, but every other week something would occur to make the bike run poorly- too rich one minute, too lean another etc. However one day after a million carb cleans with cleaner. It ran reliably for several weeks, however the bike refused to move off the line unless you slipped the clutch at 3k rpm. I was content with that for a while, and perhaps thought it was what people complained about. A year later it skidded down the road on wet leaves. However- immediately after picking it up and going on again, I noticed the torque it now had under 3k rpm which it didn’t previously have! Strange- yes.

Since then, it is quite easy to rolling start the bike at say 5 mph in 2nd gear and it is quite open to changing to third at 20mph etc. It doesn’t complain doing this (needle position is 4th from top).

2016 I bought a 251, in a very sorry state, but.. With standard carburettor adjustments, I also find that it is perfectly happy to ride at 40mph in top so long as the ground is level. It has a very similar performance than my etz250. Both bikes have their original carburettors (etz250 30n2.5 @ 32k, etz251 30n3 @ 48k), and both run about 30ish:1 premix (and have ever since I purchased them). Both also have nice linear torque curve, with no sudden ‘power bands’, which is actually my preference anyway.

I have also ridden other etz250’s and feel that they are perfectly find below the 3k range.. Sure it isn’t kick your teeth in performance, but the bikes DO have torque if you overgear them when the conditions are right. With the introduction of my es250/2, I finally have the opportunity to compare the different engines with that of the etz’s. Though it is a slow project at the minute so riding far isn’t too much of an option until it gains my trust.

Matthew

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