Can anyone recommend gear oil for a 1990 ETZ251? I have a choice of Silkolene Super4 (4 stroke oil) SAE10W/40, or Mobil Mobilube 1 SHC fully synthetic gear oil SAE 75W-90. I have drained off the old oil and want to ensure an appropriate replacement.
Author Archives: Chris Williams
Carburettor issues on MZ251 and ULEZ
Hi everyone,
First the good news – my 251 is Ulez compliant (£175 less in my pocket though)
The less good is that the substituted Japanese carburettor with which said Ulez compliance was obtained appeared good to start with but has become problematic – in fact it became very difficult to get a stable tick over and smoked more than MZs usually do!
My solution is going back to the drawing board and renovating the original BVF 30- N- 3-1 carb using a supposedly identically one I had tried earlier but which is inferior overall in metal quality and fit.
My question is about whether a) the pilot air screw absolutely needs an o- ring as neither the original, nor the ‘not so cheap’ “identical” substitute had one. Also there seems lots of different views about turns out for both the pilot and the bypass air screws – any thoughts on this are very welcome. The 251 has done about 32k since new in 1990.
Hopefully if all sorted and passes MOT I may see some of you at the ACE cafe for Red Oktober meet on 13th October.

For sale Sym 125 scooter 2019 – under 2,000 miles
Valuations for insurance purposes
Hi everyone,
Can anyone help with a market valuation or best estimate for my restored 1990 G reg MZ251? It looks very clean and original, runs well with a new carburettor and has electronic ignition fitted. It has just had MOT renewed. It has done around 32K miles. The insurance is up for renewal and they recommend checking on value. I am estimating around £2,000. Has anyone bought or sold one recently? Many thanks in anticipation.
ETZ251 carburettor trials!
Having recently fitted a tezet electronic ignition system and had some good running with a replacement BVF 3N30 carburettor, I now find myself unable to get the engine started – it appears to be a fuel starvation problem. In an effort to try something more reliable I have now fitted a PWK alternative but still seem to have the same problem. Any creative suggestions for reliable carburation for my 1990 machine?
E10 unleaded petrol – can we use it?
Hi everyone,
Is there any technical information available for the use of the new fuel in MZ motorcycles. I haven’t been able to find anything to say yes or no. I’ve recently topped up the petrol tank in my 1990 MZ 251 ETZ with it in but not sure if it will damage it or if it’s safe for regular or occasional filling.
Kind regards,
Chris
Exhaust leak at clamp joint on ETZ 251 and front wheel bind
Hi everyone,
Looking for answers to the two small issues pre taking restored motorcycle to its first MOT for 16 years!
On tick over and a little light revving in the shed I have noticed a dribble of oiliness coming from under the clamp holding the down pipe and silencer together. I have tightened the clamp up and it has diminished but still drips a bit. Is there supposed to be a gasket there as I can’t seem to find reference to one other than possibly an ‘exhaust elbow gasket’ but no clue as to where or how to fit it and the shape seems wrong!
The other issue is a slight bind on the brake pads which happens for about a quarter of the front wheel turn. It doesn’t stop the wheel turn and I think the disc is true and the wheel looks true and I’m not personally overconcerned but I want it to pass the MOT! grateful for any help. Kind regards, Chris
Tax and MOT for restored motorcycle
Hi fellow MZ riders,
I’ve just restored my MZ251 ETZ solo m/cycle. It has been SORN since 2006 although DVLC ceased sending me SORN declaration demands after 2013. I now wish to get it back on the road, particularly as I’ve invested a great deal in getting it back into a good condition and want to remind myself of the pleasure of riding it! Do I need to notify DVLC before I seek to insure it and have it MOT’d as I won’t be able to get it taxed beforehand. Anyone with recent experience of this?
Kind regards to all fellow restorers and MZ lovers.
Chris
Dismantling generator on ETZ251 – how to undo rotor?
Hi everyone,
I’ve acquired a Tezet electronic ignition kit to replace the points system on my 1990 ETZ 251. Trouble is the Haynes Manual does not describe or show how to remove the existing generator from the engine. Allen key on central bolt merely turns the engine over like the kick start. Do I need a special tool to remove the generator? Thanks in advance for any help with this
Help needed Oil pump on MZ251 air lock near crankcase
Hi everyone,
I am trying to get my 1990 MZ 251 back on the road after 16 years in the shed! I have just changed the feed pipe from the 2 stroke oil container to the oil pump and I am happy that this has no air lock as I have now bled it. However, the small pipe from the pump to the crankcase has also been replaced by me but a few air bubbles remain after filling it with oil and reconnecting to pump and crankcase spigots, and I cannot work out how to further bleed this pipe – will the pump push out these air bubbles (air locks?) when I eventually get the engine started, or do I need somehow to remove them beforehand, and if so, how, as the pump will not work without the engine running, if I have understood its mechanism correctly? Any answers to be gladly received.
Carburettor priming
Can anyone tell me whether, after reconditioning the carb on my MZ251, I need to prime it first before refitting. Unfortunately I have refitted it without doing so! Fuel is flowing from the petrol tank to the inlet of the carb but none seems to be reaching the spark plug
Decarbonising exhaust on ETZ 251
Hi everyone,
When using caustic soda to clean out carbon on the long exhaust pipe, which end is bunged up?The manual is ambiguous on this and I had assumed the end of the exhaust containing the baffle would be bunged up and solution put in the other end. Any advice on the correct procedure would be appreciated.
New member – restoring MZ251
Hello, I’ve just joined as I am in the process of restoring my 1990 MZ251 and, although I can see the project end in sight, I may need some additional guidance for completing the rebuild correctly. I am pondering over adding electronic ignition and changing the carburettor but will hold off until I know it fires up with the points ignition. A current conundrum is the rear brake mechanism – I have got it working but only with the cam lever upwards, as otherwise it fouls the side stand – any ideas if this is legal or sensible?