MZ ETZ 250 Tuning — Real Classic Motorcycle Rebuild Techniques

26 Мар 2015 | Author: | Комментарии к записи MZ ETZ 250 Tuning — Real Classic Motorcycle Rebuild Techniques отключены
MZ ETZ 150

MZ ETZ 250 Tuning

Derek Pickard at the stock MZ250 carb tries the alternatives, finds works and gives the details of how to your ETZ run super sweet.

start with a few hard The BVF carb as fitted to the MZ two-strokes can be considered ‘average’ in its metallurgy and It is the main contributor to bad starting and running. As the carb wears, bad behaviour gets worse.

can be corrected by replacement. The trick is to which carb and how to make it fit and

We all like the unique MZ 250. The works well as a good rider but it does mean a few compromises. As the years pass and engine bits are replaced, few go to the expense of fitting a new carb.

Yet the BVF wear and with it goes any of settings which means out on easy starting, best smooth over-run and maximum

My ETZ250 had done over km and like all 25 year old bikes has had engine and transmission parts But the original East German BVF was a worn old carb. Rather putting money into it, I decided I’d take on a of finding which alternative did albeit from a position of carb tuning experience the years, including Amal and

The most obvious replacement is to a good Bing and mounting from a later model MZ But those carbs have covered a high mileage and are which means they are to be a good upgrade.

See something different? This is a Mikuni VM30 looks on an ETZ250. Not much change but the performance is a big upgrade.

Just everybody these days that the carbs which ever wear are the top-rated These Japanese carbs the best materials and machining is why they go on for decades with a slide/body fit to match their top Even old ones show up as in great condition — at the other end of the carb rating old Amals are usually best for keeping fishing lines Here’s the results of my investigation:-

For the 30mm is the correct size but it is unobtainable from breakers very few old Jap bikes used size. So for the bargain hunter, the is to go the next size down and use a as fitted to older Jap bikes as the 1970s Yamaha RD350 and 250s. The problem is they are a bodied carb so special will have to be made for the and rear to fit into an MZ.

These the VM28 to exactly the right and diameters — but be careful to the front one an exact fit or an air leak result. (Don’t worry too about the 2mm drop in venturi as such a reduction may well a couple of bhp at the top end but there shouldn’t be difference in the effective torque town. And don’t fit a VM32 a 30mm inlet as that work worse than a

My ETZ 250 runs well on such a conversion which was my first upgrade and I was delighted at the improvements. If you access to someone who can make sleeves then this would make a very improvement for a commuter or tourer.

Concentric Mk1

This British may well have been of the Empire but it is rather crude and for not giving a reliable tickover. a chrome plated brass from Surrey Cycles gives a tickover but there’s the additional expense of buying the front fitting that it from a flange to a push-on mount. Beware buying old Mk1s as most were with a pressed-in size 25 which can’t be removed.

I accept the Mk1 has the advantage of offering a tickler flooding device for starting and can be very cheap to buy a one, all-in-all I’m not a fan of carb. The Mk1 metallurgy and machining is than the BVF and it cannot be an improvement on a 250 so I didn’t test one on my ETZ.

Concentric Mk2

Since Burlen UK maker of the Amal Carb has reduced the new price of this it is worth considering, and for a little money the Teflon-coated slide can be Fitting means making a thin (14 thou wall sleeve for the front so it accurately into the MZ female fitting by just under 40mm.

Also, it involves turning the large rear inlet from 60 to 52mm which may ugly by exposing a couple of but these are covered again by the MZ air sleeve rubber. And remember ordering to request a ‘left’ one so the adjustment screws are more accessed.

An interesting comparison this and the stock carb is the difference in weight. MZ must cast their carbs out of the alloys with lots of or lead which is illustrated by a BVF in one hand and an Amal Mk2 in the other. The comparison is something like a house brick and an empty box of

Presumably, Amal use plain aluminium. (Be advised that Amal needs a two-… tube where the top is angled at 30 degrees. Also, the pilot jet be fitted in the front of the two positions.)

For open road work, the is only a 250 and so needs every bhp which comes from the size 30mm carb. A is the best and this may be the most at Ј105 from the UK but it has the advantage of superb at everything in carburetion. It optimises the engine for the best in pick-up and economy. If it is possible to close to bolting on the precision of injection, then a new Mikuni is it.

These VM Mikunis are a very instrument and a heck of a lot of variations in and jets are available so some may the tuning difficult and expensive. But I mine from Mikuni Allens Performance who supplied it jetted.

However, again, a needs making as the rear can’t be turned down. means making a difficult spacer for the rear that the push-on end from 57 to 52mm OD for the MZ air I made mine 2mm thick out of A difficult thing to make but The fit is tight and a couple of things be remembered.

Firstly it is necessary to take off a thou or so from the front OD by hand with say 180 paper which will the stock VM to slide into the MZ This is done for fit as much as the off the as-cast semi-rough finish for an seal.

Then it is necessary to the two MZ carb clamping bolts thinning down the heads so in the inverted position these clear the front of large VM chamber that unavoidably very close. And because VM with the rear stepper is longer than the stock heaving it into place is a squeeze but it can be done. When to all other carbs the VM32 is a delight.

My ETZ250 is now far more usually requiring no more two kicks to start and runs on every time. Definitely a bike.

As the stock BVF is inevitably worn and best replaced, the 250 has a few options. Finding an old VM28 left) can be cheap but front fitting sleeves must be An Amal Concentric Mk2 (top with a Teflon slide okay but both a thin sleeve must be made and the trumpet must be turned to fit onto the MZ air filter attachment.

The VM30 Mikuni (bottom is the last word in optimising an carburetion but the rear needs a sleeve for the air filter join. Any one of three carbs will the ETZ250 starting and running an old BVF.

After-Thoughts: Power

In of outright power, just all 30mm carbs can produce the same top end if the main jet is right. But not the same because as the Mk2 casting has a lot in with other Amal the all-important trumpet effect the venturi has too many compromising and cannot flow air as well as the But in reality we’re only a tiny difference at the very top Interestingly, the BVF has a superb air flow pity the rest of it is so bad.

Yet proof that the East engineers knew the correct but couldn№t get the right materials and

Cable Versus Lever

both Mikuni and Amal have chokes that can be by lever or cable, the latter is The reason is a simple on or off is inadequate in not a setting of only partially on for for a winter morning. It all adds to the of a good system.

It is definitely possible to transform the of an old MZ two-…: fit a new Mikuni for 105 quid and the new inlet sleeve made. You believe how much better bike will run.


40 pilot 1 turn out

MZ ETZ 150
MZ ETZ 150

5F3 second notch

N-8 or P-5 needle jet


140 main

2 air

Amal Concentric Mk2

25 pilot front position 1 out

2D1 needle mid or number 2 notch

107 jet

3 slide

210 main

50 starter

2.5 air


150 main

45 pilot 1.5 out

6DH3 needle mid-notch

P-5 jet

2.5 slide

MZ ETZ 150
MZ ETZ 150
MZ ETZ 150
MZ ETZ 150
MZ ETZ 150

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