MZ won't start

[JawasandMZs]

Please help!
Bought an etz 250 in september and quickly found the crankseals were shot. £650 for a rebuild so we're immediately up to £1550. Whilst waiting for the engine to come back I painted the bike, had a rack built and bought panniers. Price so far .. £1700, also fitted a new brake light switch new speedo cable new fuel tap because they're made of plastic so break really easily..duh nice one MZ.

Imagine how pi.... unhappy I was when I installed the rebuilt engine and it won't start. I've had the carb off, nothing wrong with it. When I put it back it started leaking .. Gr rrr ! I soived this by applying gasket seal between the carb body and float bowl.
So.. rebuilt engine, big fat spark, have tried hooking it up to a car battery. Plug is brand new b8hs. Brand new air filter. It was running, though badly, prior to rebuild. Plug is getting wet. Plug is sparking, petrol in cylinder, won't start. Had the points set soon after buying the bike. That was another £70!
Im up to two thousand quid and still haven't ridden this bike. Oh, plus insurance and tax. It's driving me mad, Im on the brink of chucking it on ebay and writing off a months wages and hours wnd hours of stress because Im truly starting to hate this bike. What a total money pit.
Is there anything else i can try? My bike shop is baffled. IM baffled. Im counting on soneone out there knowing something, ANYTHING, that the Haynes manual doesn't.


PLEASE SOMEONE HELP ME.

[Blurredman]

Hi,

Where do you live out of interest- maybe there is someone close?


For a start, I'm not sure using gasket seal to stop carb overflow is really a good idea. They can leak through the bowl gasket, but that might be because the float height is not set correctly?
If the fuel isn't escaping though the gasket- potentially it is just being dumped straight into the engine..


I would use a 7 grade NGK spark plug for the etz 250 or equivilant like a W22FSU by Denso etc.


Are you not mechanically inclined yourself? I would guess not if you let someone charge £70 just to check the points/timing.. That is a rip off- But I guess that was a shop.



Don't give up hope though.. We've all been there with bikes that we have considered leaving in a ditch and never looking back. My ETZ 251 for one.. I felt so annoyed and started hating it.. But I solved each problem as they arose, one at a time, and now.. It's one of my major commutor bikes, and i've been abroad with it too for holidays.

[Puffs]

Welcome JawasandMZs, though it sounds you've not been very lucky or happy...

IMO Blurredman is correct in all he's saying; esp. you should not try to seal the float bowl if it is overflowing. Fuel enters that bowl via a valve (the float needle valve, 15 in fig 2.3, P75 of the Haynes manual), and that's the one that should close off the flow when the set level is reached. If that valve seals poorly (either worn, or corrosion on the seat due to not being used for a long time, or dirt), then the level is too high, the bike floods & won't start. Making sure it doesn't overflow at the edge of the bowl just causes the fuel to flow straight into the barrel - gravity dictates it has to go somewhere.

In fact, some carbs have a hole at the top of the bowl to prevent fuel spilling into the engine, and act as a tell-tale that you have an issue.

An NGK 7 or 8, and ETZ250 should run with either, but I mostly used a 7.

These engines are quite basic and understandable, and a good place to acquire the art of motorcycle maintenance (Haynes is OK, but don't be guided by Mr. Pirsig on technical matters). If it has a suitable spark, at roughly the right time, compression, and a suitable fuel/air mixture, it should run. Remain calm and composed, and tackle each problem as it comes in pursuit of the Zen. But with an old bike (31 to 39 years for an ETZ250) you should be prepared to do most of the work yourself, otherwise it'll get to be quite expensive.

I suggest to take the carb off again, and take that fuel valve out, take that apart & inspect/clean it. And check that it seals properly, for instance by inverting the carb (upside-down) & check with your mouth that the valve then seals.
(That might need a bit of fuel pipe, and avoid swallowing fuel as you'll burp the flavour up for days.)

The engine will now be flooded, i.e. there'll be a pool of fuel inside the crankcase. With the fuel cock (which MZ made of metal, if I remember correctly) closed and the throttle wide open, and the spark plug removed (& ignition off), kick the bike many times. On the kick starter that is. Or better still, push it in 1st gear. Anyway, all in an attempt to get rid of that surplus of fuel. Then fit the plug & start the bike the normal way.

Good luck!

[dave47]

If I was in this situation the first thing I would do is check that the timing had been done correctly.
The Haynes manual, ETZ 1991, doesn't tell you how to do this without a dial gauge indicator, but a simpler tool is available, just google etz timing.

[JawasandMZs]

Thanks for your replies. Live in South Wales, cf827nh. The sealing compound isn't there to close the overflow pipe but the seal the surface between the the float bowl and carb body as the gasket doesn't seal properly me having the carb in bits literally 50 times. The carb is inclined downhill towards the engine at the front so the petrol height is slightly above the gasket.
Ive tried filling the carb whilst off the bike then carefully withdrawing the bowl and it fills up nicely to within 0.5 mm of the top of the overflow pipe. The body of the fuel tap is brass but the nipple that comes off the fuel tap is plastic and split after so many times pushing the pipe on and off.

Is there any merit to using a genuine replacement carb in preference to the suspiciously cheap ones on ebay?

Incidentally I bought this mz because I ride a 2015 jawa 640 twin which is so good you'd think Honda were now making them under licence an the MZ was meant to be an ..err, don't laugh .. voice fades to sheepish whisper...as an investment. Oh dear.

Any other ideas, folks?? No, i have zero mechanical expertise and the little I do know Ive had to learn on my own the hard way. When i finally get it fixed gonna install vape and be done with points condensor and all the other prehistoric tin boxes:)

[Blurredman]

You my friend, live 2.2 miles from me.. how odd..

Intruiging - I thought I saw a smokey old thing going into Hengoed the other week..


I can pop around and see what's what if you like?


Throw me some dates and times and I will have to see what I can accomodate.

[JawasandMZs]

Blurredman, like are you for real? Omg. My name is Tom Bartram my number is 01443 551414. Mob 0741 303 6432 Just got back from ystrad mynach hospital ... having had a dislocated big toe pushed back from the evil kick-back of the mz!
Managed to get the beast going for a couple of mins by pouring petrol str8 down the plug hole. So the prob is clearly on the carburation side

[tigcraft]

@jawasandmzs you could do with editing out your phone numbers for a piece of mind and pm instead. I noticed you’ve spent an eye watering amount on this bike. These bikes have never been in that ££££££ sort of ownerships because they’ve been a ‘fixit and learn’ bikes.
With mine I’ve enjoyed every minute of tinkering as simplicity is bliss for me. The new available parts are currently for nothing and a pleasure to fit. I hope you get round to enjoying the other things about them as well as riding.

[Puffs]

As tigcraft says. Best remove all personal details from an open forum. Share what you will with Blurredman and I'm sure he'll find the issue.
And indeed, these bikes are a good place to learn, and with excellent parts availability.
Value-wise, you're in the €2k range, which for a good ETZ250 is not unusual in Germany. Value is a local thing, but also in the UK it might go up (significantly).

Good the bike has now been speaking! And judging by the toe, the thing has compression, and maybe it is an ignition problem too? If it's just been reassembled, it could have 2 problems at the same time.

Btw, I have a Jawa 634, a slightly older predecessor of your 640. I presume those recent 640's that were imported into the UK are Indian?

[JawasandMZs]

To be honest on price, two grand for bike that gives me potentially years and thousands of miles of fun isn't a waste of money. Where I HAVE wasted money over the years is on bikes that I buy, get bored with in five minutes (after having replaced the tyres, chain and sprockets, and done the fork seals etc) then sell for less than I paid.
I paid three grand for my jawa and don't regret a single penny.

[JawasandMZs]

The Jawa 640, known the Classic, is Czech built and can be purchased brand for £3895 from F2 motorcycles of Wisbech. It differs from the 1991 version in having electric start, a front disc the size of a dustbin lid and a modern charging and ignition system. Mine has done over 10000 miles and it's still loosening up and getting faster. Cruising speed is 65mph at just over 4000 rpm.

On the topic of telling you all who I am ... how many of you have bought stuff over the phone by telling a total stranger your card details and three digit security code on the back of the card??!!

[Blurredman]

I'll give you a call when I can Tom.





And I agree, who does not remember visiting websites asking for card details to purchase items, before e-Bay and Paypal - you weren't always quite sure if you were opening up to fraud. And I suppose........putting your telephone number here is no different than being in 'the phone book'. And that used to have your address in it too, potentially..

[JawasandMZs]

Hurray! Hurray! Bike's going! Problem solved! The crankseals were gone causing white smoke so obviously I had the carb on and off impteen times completely needlessly.
The float bowl gasket started to leak. So I blamed the float level (wrong) and lowered the float height, starving the engine e. D'oh! So obvious!
I've actually put on a brand new genuine MZ carb. Ha! Problem solved...

...BUT ...

how the heck are you meant to adjust the tickler with the late etz250/251 carb?

The throttle slide sits so low that NO air gets through. I noticed this when I installed the slider into the carb body. Duh.

Anyone know? I hold the throttle slightly open whilst at the lights. I'd like to set the tick over at about 1750.

[Puffs]

Privacy & security: to each his own.
But to me a 1-to-1 exchange is quite different from a global announcement. In a 1-to-1 exchange you know who you're dealing with, when you post something visible to the whole world, it is available to anyone, and that might be a start of identity fraud.

Yes, I know of the 640, but I figured production had moved to India as a result of their liaison with Mahindra. Details are not clear to me, but like RE, India is now a big market to them. https://www.jawamotorcycles.com/news/it ... -this-year

Good to hear you have the bike going!

...BUT...

Assuming you have a 30 N 3 carb: Which tickler?

075.jpg (23.97 KiB) Viewed 117 times

For idle speed, that carb has a bypass circuit:

Leerlauf 30N3-1.jpg (26.65 KiB) Viewed 117 times

Adjustment is explained in section 9, page 77 of Haynes: ftp://blurredmanswebsite.ddns.net/Vehic ... es/077.jpg,
or the original (German) on page 66 of ftp://blurredmanswebsite.ddns.net/Vehic ... TZ-251.pdf