Das MZ Forum für MZ Fahrer

Hi there...

Need help
my es 250/2 engine has been restored before 6000 km,bearings,seals,piston,crankshaft have been replaced.
Powerdyanmo 12v 180w has been installed.

Metal rattling noises started coming from the engine a month ago.
the sound is only present when I apply a full throttle,engine is hot,only in 3 and 4 th gear.
and only between 4300-5100 rpm
example...I am driving 60 km/h in the 3 rd gear
and then I apply full throttle
while accelarating,the engine produces this rattling metal sound between 4300-5100 rpm

It souns like this:
https://www.youtube.com/watch?v=lGC51mIQylk

How can I fix it?

Things that I have tried:
-Switced from bvf 28n to 30n
-more 2 stroke oil
-checked the gearbox oil,
-replaced the spark plug
-tried to set ignition a bit forward and rearward
-removed the cilinder and cilinder head and did an inspection of piston,piston rings,piston and crankshaft bearing

All this things did NOT help.

My next step is to replace piston bearing.

Do you have any idea???

It's sounds like a carburator problem or a problem with inleake air. Please sputter the area between the carburator and the cylindre with disk break cleaner. If the engine will cange the course, than it's an inleake-air-problem. Do you have a fuel level of 14 mm at the carburator float?

In usual cases the ignition point of the Powerdynamo is to close to the top dead center (~1,5 mm before top dead center). It should be at 2,75 mm to 3,00 mm before top dead center. Otherwise the engine, especially the crankshaft, will fail immediately.

I have adjusted both carburetors according this photo from the mz manual


The bvf 28n I used until a month ago had its own suction connection and the 30n now has its own.I decided for the 30n because of the idle screw.

Today I also completly changed the fuel (eurosuper 100 to 95) and this time I did not add a lead additive I normally use.
Also I switched from the Rowe syntetic to a Castrol Syntetic 2T oil with mix ratio little bit above 1:50

Piston bearing replacement is in progress...hope it will solve the problem

Which size have the main jet?

Main jet is 140

Than i only can imagine that the ignition point not fit, like Christoph said...

I have tried to set the ignition a bit forward and then backward and the sound is still present.
The ignition is powerdynamo 12v 180w

...ich kann zwar das geschriebene Englisch verstehend lesen, aber mit dem Schreiben tue ich mich schwer...
... er schreibt "das Geräusch kommt nur bei Vollgas " ? Somit müsste Schieberklappern fast auszuschließen sein...bleibt der Zündzeitpunkt und die Falschluft...bzw. zu wenig Sprit ... wobei die Größe der Hauptdüse dagegen spricht ... interessant wären das Kerzenbild und der Auspuff...

The color of the sparkplug is the way it should be/caramel brown and I will post a photo tomorrow.

Last week I had fuel with 100 octanes and 2.5 % rowe 2T syntetic oil and then I added 1% more of stihl 2T mineral oil and plus lead additive...all together made a rich mixture and the noise was still present.

The noise starts when accelerating from 4300-5100 rpm,when engine is hot and under load/has to accelerate rapidly.Same as in the video I posted.

I have to check some other things tomorrow


Thanks for answers

An what is the Result, if you put the Needle in the Carburator 1 Step higher ?
(to do that,put the Plate 1 Step deeper)

It is difficult to say that in enlish, in Germany we say: The Motor "knistert"

The color of the sparplug changes a little bit,less smoke comes out the exhaust...depending on the position of needle and the amout of 2T oil in the/mixed with fuel

The synthetic oil isn't for aircooled engines...because they will run much hotter than the water cooled...take normal mineralic oil

here a very short Video Simson tickling Noise:
https://www.youtube.com/watch?v=8UxTF0nnzbw

This is the "Knister" Noise if the Carburator setting is too lean in full Throttle !
Bye
ertz.

...sometimes it is better to drive , than to hear about thomething ... may be it is only an old Caburator....?
... do you have the possibility to change the ignition parts to the original ?

If the color of the sparkplug is ok,can the engine have lean mixture?

What position of carburetor needle would you recommend for ts 250 carburetor?

The sound in simson video is almost identical as mine.

I have to check more closely if there is damage caused by lean mixture...

....mixture 1:50 is ok... there is a Problem with the volume of gas and air , may be
.... or there is no probleme and you have to drive with your bike and have to watch it....

Hi,
i think the engine runs to lean esp. on full throttle, too.
Change the position of the carburetor needle and/or change the bore of the main jet.
Have a look at air leaks as Christof told you.

Thank you all for help

You were right.It seems that the engine was running lean on high revs and has made a few signs/marks on piston that were not visible before cleaning

After that damage being done no oil or max mixture could fix the problem

I have replaced the piston and after a carefull ride couldn´t hear any noise.

Now the needle is in the middle position and the fuel mixture is about 3% because of the new piston.

After a very long time of troubleshooting;TS 250/1 5 speed engine now installed,2x es 250/2 cylinder/head sets and now ts 250/1 cylinder with ts 250/0 cylinder head,3x carburetor intakes,2x bvf 30n carburetors with different main jets(135,140,145),ignition retarted to -2.7 bdct,several types of sparkplugs withdifferent heat range(now ngk 8 range),exhaust completely cleaned,3x fuel taps,different 2t oil in different % from 2% to 4%(mineral to semi sintetic),providing more air to carb with aditional holes in air filter casing...

WHY can´t I get the BVF 30N carburetor to work normally without SPARK KNOCK in 4th and 5th gear while throttlee is fully applied(area from 4500-5500 rpm)

With BVF 28N 1-3 there is no spark knock present...

Hello Mario, my engine gave me trouble with strange firing in the higher revs last year. It sounded like a four stroke engine almost. Turns out it was running too rich! I put the carb needle down one nodge and all was well. Cheers!

Puting the carb needle down one knodge will only make the sound/spark knock be more louder and more frequant...the needle on BVF 30n is in full up position while on Bvf 28n two knodge lower and like I wrote;no spark knock present with bvf 28n

hallo


A larger carburetor with its accompanying larger bore will have a lower Venturi speed at Full Throttle.....
thetefore you will run lean.

too big, and it will tend to be sluggish with changes in throttle setting.

raise the fuel level and get a larger main jet

substitute "will" for "wants" dumb translator is stubborn.

Thanks for answer.
The thing that doesn't make sense to me is that every thing except carburetor intake and air filter housing was the same as in ts model...Does an original ts 250/0 or ts 250/1 make spark knock?
And it doesn't make sense to install main jet bigger than 150 cause the fuel consumption will increase.

no spark knock, and sensitive to float level.

https://youtu.be/kQjrO0rPj5c
I have decided to give a "keihin" pe28 a try

Conclusion;
Too early ignition combined with bigger carburetor bvf 30n,hot sparkplug(during one period of time) and using cheaper semi syntetic 2t oils made engine to overheat and cylinder to wear out/compression to decrease.

Few things about 2t oils:
http://www.dragonfly75.com/motorbike/oil.html

It seems that for our old air cooled mz engines it is important that the 2t oil has higher viscosity at high temperatures(100 celsius).Usually better mineral oils like stihl or castrol 2t or more expensive syntetic 2t oils like motul 800 and repsol moto racing 2t have viscosity number at 100 celsius around or higher than 12 .