MZ Riders Club

MZ Riders Club

Hints and Tips : Two-stroke

Page updated : 27/12/2005

Site designed by Mike

In no particular order

Starting Procedure: For those of you who may be new to MZ 2-strokes (there’s got to be at least one of you out there who is) here is the ‘Kick Start Technique’ as recommended by original MZ importer Wilf Green. It’s as follows:

Turn choke on (But leave ignition turned OFF).
Kick bike over twice.
Turn choke off.
Turn ignition ON.
Firmly kick bike over.
It should now start at 1^st or 2^nd attempt.

Note: DON'T keep twisting the throttle as you do this as the bike will flood and it won't start. However, if you do flood the bike by kicking it continuously without it starting you should turn the petrol off at the tap and open the throttle fully. Now, as you kick it over the excess fuel is expelled until the mix is sufficient to start up, usually with a lovely dense cloud of smoke as well. Remember to turn petrol back on once you manage to get it going, though, or your journey is likely to be a short one.

New Coil & Regulator: (Mike) I recently decided to replace the original coil and mechanical regulator on my ETZ251. So, to that end I acquired a coil, designed for use in a Mini, HT lead for it from Halfords, and a Lucas electronic voltage regulator (part no. NCB 403), as fitted to various cars and bikes. One Saturday morning with the parts in hand, a copy of Hints & Tips Vol.2 for reference, a couple of bottles of beer and a new CD that I’d just bought for inspiration I made for the shed. I had nothing else planned and was determined to get everything done in one go.

The instructions for fitting a replacement regulator in H&T2 (available on Regalia site on Links page) are pretty straightforward. In fact, there are three or four different lots from which to choose, but for those of you who don’t have a copy (and why not?) I’ll repeat them here with my own observations thrown in for good measure:

With the seat off the first thing that you should do is disconnect the battery. This is in case you accidentally short-circuit anything. Pull the wires (5 terminals) off the regulator (don’t forget the earth wire, bottom left as you face the front of the bike). Remove the old regulator by pushing the rubber spigot (bottom right) through the clip on the frame with a screwdriver (be careful with this as we’ll need the clip later). Make a small bracket to attach the new regulator to the bike. Connect the brown, green/blue and green/red wires to the new regulator. Bolt the regulator and bracket in place. I fitted the regulator with its rear against the petrol tank and the terminals facing backwards. That way there’s no need to fiddle with the various wires for length. Next fit an inline fuse holder with a 15A fuse between the red/yellow and red wires (the thick ones). On the original regulator the connection between the red/yellow and red wires (terminals D+ and 51) is a current limiter which cuts out if the current goes above 15A. This would only normally happen if a short circuit occurred. The 15A fuse in the inline holder would blow if this were to happen now. However, from talking to an electrician of my acquaintance recently it seems that the fitting of the inline fuse is a bit of overkill and is strictly speaking unnecessary. However, I fitted one because I had bought one and it's better to be safe than sorry, right?

MZ regulator Lucas regulator

D brown D-

DF green/blue DF

61 green/red D+

D+ red/yellow across 15A fuse

51 red across 15A fuse

The longest job I found was making up the bracket to attach the regulator to the bike. I cut a small square metal plate to the size of the regulator and drilled a couple of holes in it to line up with the ones on the regulator. A small bolt through the hole on the left of the regulator, a longer one through the one on the right when viewed fitted as described before. I then bent the clip that the original regulator was mounted to so that the longer bolt could run through it and tightened up the bolt with a couple of large washers. This holds the regulator in place and the shape and size of the square plate prevent it from moving around. Sorted!

Next up was the coil. Remove the original coil by loosening the bolts which mount the bracket around the coil to the bikes frame. The new coil, designed for a car, is quite a bit larger than the original MZ one and, no surprises, it won’t fit the original bracket so you’ll have to make up another one. Luckily the coil I had bought came with a metal bracket which I re-shaped (hit with a big rubber mallet until it was the right shape) before attaching it to one of the original mounting points on the bikes frame. There are also a couple of additional spade connectors attached to the terminals on the car coil. These can be safely removed as they won’t be needed. Connect the wires to the terminals.

MZ coil new coil

1 green (-)

15 red/black (+)

Be careful when mounting the new coil as it’s a bit of a tight fit under the seat. Make sure that the terminals don’t touch anything metal or you’ll start blowing fuses. If this happens when you’re riding along the bike will simply cut out on you and you’ll lose power and all your lights. This is what happened to me when I mounted the coil using just cable ties instead of a proper bracket. Not too clever at night on the motorway, I can tell you. Right, that should be the coil attached to the bike. Connect one end of the lovely new, in my case orange, HT lead to the coil, cut the metal clip off the other end and screw on a standard (NGK) plug cap. You can’t re-use your old HT lead because it needs one of the clips which are attached to the new lead to connect to the coil properly. The one on the other end is surplus to requirements so it can go to make way for the plug cap.

Reconnect the battery, and you’re in business. However, before I finished up I dressed and adjusted the points as well since doing all that work and having it all come to naught because you couldn’t be bothered to take five minutes to check the points seems a bit of a waste. If you’ve got electronic ignition then this bit isn’t necessary, obviously. Everything was then treated to some silicone sealant to keep out the weather. Time taken? About 3 hours from start to finish, but that included taking all the bodywork, the seat and the rack off the bike, doing the work including making all the brackets from scratch, before putting it all back together and running the bike up and down the road to make sure everything was working properly. I’m sure that if I’d been better organised it could have been done in half of that time, but I wasn’t in any particular hurry and it was better to get it done right than get it done fast.

Points: (Mike) The normal way of setting up the points on an MZ is with a drop gauge. Now, I have seen articles explaining how to make one of these tools using an old spark plug but, with a real one costing about a fiver, only the terminally mean would waste the time needed to make something that might not work. Save yourself the hassle and buy one instead. The instructions in the factory manual are fairly straightforward and can’t really be bettered, so I won’t try. However, one thing that might be of interest to those of you thinking of attempting this manoeuvre. Instead of using, as suggested, a bulb and some wires to test when the points are open in relation to top dead centre (TDC), I find that it’s a lot easier if you use a small buzzer. Go to Maplins, or some other electrical shop, and buy a small 6v or 12v buzzer (depending on what model MZ you have) and a couple of crocodile clips. Attach the clips to the two wires attached to the buzzer and you will find this a much easier tool to use than the bulb contraption. Attach one clip to an earth point and the other to the wire clip on the points’ body. Now, when you rotate the engine the buzzer should sound when the points begin to open. Instead of trying to see whether a bulb is or isn’t lit up, which can be a bit of a struggle outside in bright sunlight, you can just listen out for the all important noise.

Spare bulbs: (Uncle Norman) If you’ve got one of the later models, 251 onwards, with the ‘square’ type rear light, it’s possible to store a spare bulb behind the lens, above the reflector (next to the connections). Wrap it in a bit of cloth/foam to stop it vibrating about.

Silencers: (Alex Frame) Whilst visiting Messrs. Burwins in London to buy a new TS 250 silencer I casually asked them how they cleaned out old, bunged ones. “Throw them on the bonfire” they replied. It took me a minute to realise they meant this literally and were not advising on disposal of same. This I found very interesting as I have a couple of clogged silencers and have never had much success with caustic soda. So, I decided to give it a try. I hack sawed an old silencer apart at the weld, then selected a secluded spot from my repertoire of cycling “drum-up” spots gathered over the years. After stoking the fire for a while until I had a sufficiently hot base to insert the silencer - I then piled on new fuel and stood back. At first pungent blue fumes were exuded (“nothing new” I thought) then it burst into flames. I left it on the fire until there was no trace of flames inside. This took 30 minutes. Whilst the deadly deed was being performed I was interrupted by a local walking his dog. I’m sure thoughts of poteen production ran through his mind, but he didn’t comment and soon left. Afterwards I removed the glowing monster from its nest and left it to cool. By this time it had lost its chrome overcoat. A brew of tea was enjoyed using the very hot embers. On inspection, I suppose it could have been re-welded (and possibly re-chromed as all the nasties which would contaminate a chromic bath were gone?), but I decided on another method. Using a strip of roofers lead straddling the joint and secured by four inch Jubilee clips, the silencer was sprayed with heatproof matt black paint. It’s smart enough for my needs, especially with winter salt to cope with. A new stainless system would have more pose effect ,but posing is low on my priority list and I’m a bit wary of using non-standard internals. After all the silencer was designed as an integral part of the engine. So, at absolutely minimal cost, and one thousand miles on, I have to consider the exercise a success, though not a roaring one. Ingredients: -

1 x u/s MZ silencer, 2 x stainless steel Jubilee clips, 1 x lead strip 12” x 2”, 1 x secluded spot from human eyes & 1 x supply of suitable wood to last 1 hour (you may find this difficult as good dry wood doesn’t grow on trees. Try a building site for off-cuts, etc.

Footnote 1: On reflection I’m not sure that cutting the silencer apart is really necessary. It was done impulsively and allowed better combustion but left its attendant problems. Who knows?

Footnote 2: Yes, in spite of all the above I did buy the new silencer from Burwins - I’ll fit it for the concours d’elegance at the annual rally.

Silencers: (Andy Tribble) For those wondering how to clean out a blocked-up silencer you might want to try the following:

1) Remove silencer
2) Jam large potato over front end of silencer until completely blocked
3) Stand silencer on end with potato at base
4) Pour litre of warm water into silencer
5) Put on rubber gloves
6) Put out cigarette
7) Pour measured amount of drain cleaner into top end
8) Stand back, try not to inhale fumes
9) Carefully remove potato and drain off fluid (at this point Uncle Norman used to remind folk to throw the potato away. Do NOT use it to make chips!)
10) Flush through with more water
11) Reassemble and run up to working temperature to boil off any remaining water - don't leave it inside.
ALL THIS IS AT YOUR OWN RISK.

6-Volt machines: (Mike) For those of you out there with an elderly 6-volt MZ it can be a real pain getting hold of headlight/indicator bulbs. If one blows you can’t just pick one up at your local garage. Help is, however, at hand. Next time you’re stuck try and find a VW/Audi dealer. The older VW Beetles are 6-volt and you can usually purchase bulbs and other small electrical items over the counter. Alternatively, if you blow a 6V bulb and can’t find a replacement a 12V bulb will do as a temporary replacement. The illumination is poor but better than nothing if you are caught out in bad weather. Needless to say this does not work well the other way round.

Easy De-Coke: (Keith Steyert) A simple way of de-coking a 2-stroke engine is to remove the plug and pore a small quantity of Redex into the engine, press a cloth over the plug hole and crank the engine over a few times. This works the Redex into the exhaust as well and is best done with the engine warm (but not essential). It may be necessary to crank the engine over a few extra times before re-fitting the spark plug to avoid hydraulically locking the piston. If the engine won’t turn over with the plug in place, remove the plug and crank the engine over a few more times, you will clear the excess Redex eventually. If you do resort to brute force and break something, don’t blame me, you have been warned. Finally leave the engine for the Redex to soak in; about half an hour will do then take the bike for a run. One last tip take the bike for a run at night or on deserted roads, the smoke screen has to be seen to be believed. As proof that this works, I have never had the head off my ETZ 251 in 42 000 miles and when the exhaust pipe was replaces it had only a light carbon coating in it.

Spark Plugs: (Keith Steyert) I have noticed that my ETZ 251 can become a little sluggish and in particular the fuel consumption slowly deteriorates. If these symptoms are ignored idling becomes a bit erratic and starting, especially with a part warm engine can be difficult. This has happened twice in recent years and on both occasions a new spark plug was all that was needed to restore the bikes performance. The old plug always looked OK, even the gap was correct, but clearly it was past its best. Plug life is usually about 6000 miles but can be a bit less for no apparent reason (but not usually less than 5000 miles). Given the price of a new plug it is worth changing it anyway if there are any engine problems. I have found cleaning plugs to be a wasted effort as this has no effect on the bike's performance or on plug life. The plugs on both my bikes (ETZ 251 and TS 250) come out with pale brown electrodes and mat black bodies suggesting that the mixture is about right. I always use an NGK B8HS.

Silencers: (Malcolm Ritch) If you need a new silencer for your ETZ125/150 then one from a TS125/150 can be fitted instead (they seem to be a lot more common second-hand). Fit to the front pipe on your ETZ as normal, using the rear mounting bar from the ETZ (with the rubber mounts) in conjunction with a small plate with two holes drilled in it approx. 30mm apart. Bolt this extra plate to the normal plate just behind the shock absorber. The performance of the bike is not affected by the earlier muffler.

Tyres: (Malcolm Ritch - 2000) I recently fitted a new set of tyres to my ETZ150. Continental are producing a new range of economy tyres called ‘Conti City’, one of which I fitted to the front. It grips very well in wet or dry conditions, was easy to fit, and was remarkably cheap (you can get a rear 3.25 or 3.50 x18” from this same range). They didn’t have a Continental in stock to fit the rear, but had a Metzeler Block ‘C’. Not bad, all in all, a new set of tyres and tubes for about fifty quid.

Tyres: (Mike - 2003) Looking for some reasonable quality/price tyres? There is a never-ending debate about this topic in MZ-circles. My preference on the two-strokes, and now on the Rotax outfit, is for Continental K112s. You’ll find them advertised as 'commuter' tyres, ie. don't fit them to a Fireblade and expect to live, but they’re more than able to cope with anything that you'll do on an MZ. You can get them in 3.25 x 16" (front) and a 3.50 x 16"(rear). Good, sensible, and cheap tyres (just like the bikes, really).

Ignition Coil: (Keith Steyert) If you have any problems with the ignition system it is worth checking the ignition coil. As I found out to my cost the coil can partially breakdown giving a spark at the plug when checked outside of the engine but no spark when the plug is re-fitted. A simple test is to disconnect the coil and check for electrical continuity and short circuit. A basic electrical tester from B&Q, Maplin, etc will do the trick. Disconnect the HT lead and LT leads from the coil. Test for electrical continuity between the two LT terminals, you should get a full-scale deflection of the needle. Also test for continuity between the HT connection and metal body of the coil, again you should get a full-scale deflection of the tester needle. Anything less and there is a possibility that you have a broken wire in the coil but remember that you must get good contact between tester probes and the coil for the reading to be correct. If in doubt repeat the test a few times. Finally, test the insulation of the coil by putting one tester probe on the HT side (HT lead or metal casing) and the other probe on an LT terminal. There should be no movement of the needle, a good sound zero. Any reading hear means that the insulation of the coil is breaking down and the coil is on the road to failure. Again it is worth repeating the test to cover all the HT / LT permutations. New coils are not expensive so if in doubt it is better to replace the coil rather than risk an unwelcome failure when you may be in a mobile phone black spot.

Silencers: (Paul Titterington ) (Imagine the next bit in a silly Michael Caine type voice..) “Did you know, that a silencer from a Jawa 350 2-stroke twin is the same bore, length and approx. volume dimension as that on an MZ 250?” You may have to make a larger back clamp, but it has the advantage of having a detachable baffle for cleaning, although it is slightly noisier. A CZ 125cc is the same pipe bore and, although slightly smaller, also has a detachable baffle for cleaning

Locking Petrol Cap: For anyone looking for a locking petrol cap that will fit most pre-1990 ETZ’s you can get one from a car accessory shop. Ask for one designed for a Mini (all Minis 1969 - onwards). It should come with two keys, and fit right out of the packet. Burwins also offer a locking petrol cap for a 251/301 and they can be contacted via the link on the Links page.

Air Filters: Those of you who are having problems getting hold of the proper air filter for your MZ (or too mean to pay the asking price) be advised that help is at hand :-

ES250/2 - the filter element from a Yamaha FZR600 apparently goes straight in without modification. The part no. is 1WG-14451-00

TS/ETZ/Rotax models - the air filter designed for use in a Morris Minor/Morris 1000 is a straight swap for the MZ one at a fraction of the price. Shop around for the best deal. Some need slight trimming, others go straight in without alteration.