Das MZ Forum für MZ Fahrer

Greetings from the prairie.
I am enjoying the '74ts250 a lot.
In top gear at 65 to 75 kph the motor humms very
sweet.

At 90 to a 100 kph , if there is no real load, as in
level ground , no wind.... there is a metallic crackle or clanking that is quite loud. Wacking the throttle open changes the sound to a moan as the MZ struggles to give its all.

I run 91 octane(premium). Plug is dark chocolate, and the mix is 40/1.

Is it a normal noise ?

Regards
Michael

Hi,
40/1? oil/fuel? 1/40 maybe. Try 1/50. When the plug is such dark the engine got to much fuel, you need to adjust the carburetor.

(sorry for my english)

hard to tell only by the description. The fuel quality is more than ok, maybe the oil-content of your fuel is a bit high. Normally you would use a 1 in 50 dilution of the oil, i.e. 1 ltr oil + 49 ltr of fuel.

Is it possible for you to make a recording/video and upload ist elsewhere (e.g.YT) so that we can have an idea of the sound....?

Can you tell if the noise comes from the cylinder/piston area or from the gearbox? Enough oil in the gearbox?

Some special noises are typical and no reason to be anxious.

can you make a video?

sometimes there is some kind of "hard" clattering noise when rotation speed goes down. try to close the "umlauftschraube" (No5) a little bit.
http://miraculis.de/aw/mz/text/ts1525b/19.jpg

Sounds like from cylinder head.
Can attempt video next weekend.
Where do I send the video to. On this site?

My needle is at the approved slot. I was very hesitant to lean out.
Idle was set by the book.
M

You could upload your video e. g. on Youtube and then post the link here.
I think it´s not possible to upload a soundfile on our forum directly.

I closed no.5 a half a turn and it did have a slight but good
effect.
Are we dealing with after burn in the pipe or as I should say, popping
from fuel that is not completely burned ?
(This happens under very light to no load)

Regards,
Michael

I don´t know why this is so... the noise can be caused by too much clearance in the upper piston rod bearing, but as far as I remember your engine was renewed lately. I had a similar noise in a newly made engine too, after reducing the amount of air at the carburetor everything works ok.

Closing no.5 leads to less air and thus a richer mixture in the idle (and partial load) system.
If the mixture was a bit too lean to start with, engine knocking (self combustion before the piston is at dead-center position) might occur and that might be the sound you heard.

So it looks like regulating the mixture was the right thing to do

Cutgjnv the throttle and coasting to the side of the road
revealed a dark brown spark plug...(edit.9/19/2015.this dirty plug almost cost me an engine because
it was discoloured from break in, giving false readings.)

If the wrist pin needle bearing was bad the engine should already have come
apart , based on experience such other two strokes .

But, MZ is not just any two stroke. :- )

++++++++ updated 5/9/15; I was able to produce the sound at lower road speeds and in a
lower gear. It appears that I am hearing an exhaust noise when over run
........ ...or very slightly trailing throttle happens and a barking appears to manifest just
before the ring ding, ding, ding sound is produced(with closed or slightly closed throttle)
You must close the throttle oh so slowly to hear this happen, on level ground, at high rpm.

Regards,
Michael

The temperatures are dropping a little every week.

Out for a ride in 60°F, air 20 mph headwind.

That crackling noise is back at about 95 kph. I try to ignore it. It gets louder!
I try to think of all the spare parts I have from Gusi . :- )

The crackle turned to a pinging and rattle so I grabbed the clutch . She stalls at 90 kph.
I am convinced that she has given up. Coast to stop, take a deep breath and kick it ever,
so , gently, expecting a crunch. Smooth. hmmm

I kick and it springs to life, I ride home at 25 kph wondering.

Next day I get a brand new plug, install it on a straight and level country road, and run
95 kph for 3 minutes. Cut throttle, and pull plug. Its snow white ! ( gasp )
I head back, driving the same way, and when the crackle turns into a ping I
pull the cold start device. The rattle stops, and she smooths out . Aha!

In the shop after looking for air leaks with a propane torch, ether spray, and carb cleaner,
I am convinced I have no air leak.

Pull the carb (vergasser?) Check and raise float level from 29 to 28 mm, raise the needle
one notch, from third notch, to the fourth notch in the bottom plate.
For added insurance I coat the carburettor spigot with heavy silicone grease.

Out on the road I do the plug chop again and its finally a very very light tan.
It runs different now, much more smooth, and firm at the top of the rpm range.

I learned.....
1) the new plug you broke in, or bedded in your new rings which is dark coffee coloured and soot coloured,
permanently and will never give you an accurate read. It simply will not come clean for me.

2) these bike can take some harsh abuse.........I cringe when I imagine what my piston looks like now.

But she is running good right now. I only hope I don't loose to much fuel economy.
I was averaging 53-55 US miles per US gallon.

Ride safe.

M-

4,2-4,4 l/100km


Here are some values for comparison:
http://www.spritmonitor.de/de/uebersich ... owerunit=2

and here you can convert:
http://www.markporthouse.net/rangie/fue ... ersion.htm

A bit more fuel consumption may safe your piston.

Hi Michael,

I think you are on the right way now to give it more fuel via carb ...
But note,

it takes normally 20 ... 30 miles until it makes sense to check the colour of the plug. After 3 minutes it looks still like a new one,
3min is tooooo short for sure ...


Please, note beside that, that the needle is only responsible for middle range throttle. For a velocity of 95 km/h and more the main jet
overtakes the fuel/air relation. Try a larger main jet, too.

Regards
Lothar

OK then,
I was not sure how far the needle can go up, so I " tried something ". Thank you for confirming
what I need.
I will get my list together for my MZ supplier........ I am hopeing he has a couple of jet sizes.
I didn't know that it took that long to colour up the plug. Thanks !
M-

-- Hinzugefügt: 19. September 2015 21:41 --

OK then,
I will get my list together for my MZ supplier........ I am hopeing he has a couple of jet sizes.
I didn't know that it took that long to colour up the plug. Thanks !
M-