ETZ 251 slow pickup between 3-4.5k revs

[thomaskwscott]

Hi guys,

I recently bought an ETZ 251 and love it. However, it is fitted with the expansion chamber exhaust and the throttle seems to be very erratic. Below 4k revs there is absolutely nothing there, then a big chunk of power between 4 and 5k, post 5k it immediately jumps 500-750 revs and heads for the sky (what is the realistic redline on these by the way?). This is becoming very annoying as i do a lot of riding two up and the odd hill can cause the revs to drop and it will simply not pick up again. Any suggestions?

Thanks

Tom

[Skorpion]

Hi Tom,

I think your problem is all down to the exhaust.
With a standard exhaust, not much power bellow 2500-3000rpm, then good to 5000rpm, and more to 6000rpm, this is the maximum revs give or take a couple of hundred, although some rev counters may say different.

6000rpm is about 85mph, and you should be able run at up to 5500rpm all day long, though this will bring your fuel consumption down to about 40-45mpg.

So change the pipe and enjoy a less frenetic ride.

[thomaskwscott]

Hi,

Thanks for the quick response. What you are saying makes a lot of sense, the pipe looks cool and is probably great when flat out for 20 miles on a track. However for long distance riding the standard may be a lot better. Do you know any good sources of standard pipes?

Thanks

Tom

[Skorpion]

Tom,

ebay is a good source of S/H parts,
but
Burwins MZ Spares has them advertised at £58. Tel 020 7359 3050

Also you could check out,
Fred Rogers
Spares & Repairs
Tel 01606 593638

These are probably the best MZ two-stroke part suppliers in the UK.

May also be of help.

John Ashdown @ Eco Spares
Tel 01455 292688

You may also wish to join the MZRiders Club who have meetings throughout the country, as members usually have garage's full of parts they may want to sell, and are very good for advice.

[claude]

Hello,
I've red all this exchange and it reminds me a problem I've got with my 250 ETZ. Many things are linked in a 2 stroke engine. For example, I've had hiccupings between 5000 rpm to 5500 and after many tests, it appears that it was because of the guenuine air filter, to much restrictive, may be not fitting the expansion chamber exhaust I've put. The problem vanished with a K&N filter and with a widely opened air filter cup !
If your problem comes from the exhaust, you could extend the length of your exhaust in order to make it efficient at a lower engine speed (more it is long, more torque you get). But if your engine is not more powerfull than a guenuine ETZ 251, maybe it is not because of the exhaust. In this case, it could be a consequence of your ignition, with a ignition point too late (not enough advance). Another reason, specially if your engine is not powerfull, is a too weak compression... Is your exhaust the same than the mine one ? You can see my exhaust on the page here at the bottom, and you will see all the mods I've implemented on my ETZ 250 (including the air filter cup that changed many things, and the cranckshadt lightening, etc...)...


http://strv.pagesperso-orange.fr/motodesign/UKETZ.htm

[thomaskwscott]

hi everyone,

very sorry for the late reply, I have been too busy to check on the mz for ages. thanks for all the answers, I plan to attack it in this order this weekend:

timing
exhaust clogged
air filter

anyone think of anything else I should check. I decided some routine maintenance was probably a good idea before splashing out on a new exhaust.

thanks
tom

[Skorpion]

Hi Tom.

I think you could rule out the clogged air filter, as you say the bike revs so it seems to be getting enough air, same with the exhaust if blocked you would not go fast

You could try looking at the carburetter, it my be running too weak at the bottom end,

Good Luck.

[thomaskwscott]

Hi Guys,

Chjecked everything yesterday. Everything checked out great so i went back to google for some answers. I've finally tied the exhaust i have on the bike down to this one:

http://rzt.de/index.php?page=shop.produ ... &Itemid=29

Which means it's probably way too highly tuned for the standard motor and for riding two up. I'll change it for a standard one this week and let you know.

Thanks

Tom

[claude]

I have the same exhaust on my 250 ETZ and without any modification on the engine (except for lightening and balancing the cranckshaft and the clutch but it is not expected to improve the power) my engine is able to reach 7000rpm very quickly and easily. And since I had removed the air filter for a K&N one and modified the air box cup and increased the advance, the engine is linear from 3300rpm to 6500rpm. I remenber I've modified too the needle position in the carburettor, I put it on the poorest level.

I don't think that your exhaust is too ambitious for your engine, I suggest you to check your ignition point, and to optimize the needle position. Then, if no change, you could drive your motorbike without the airfilter and its cover just to check if there is a change.

The other avantage of such an exhaust is the wieght : may be you save 8 kilos from the guenuine one! Is is worthwile... Ant it is a beautiful expansion chamber exhaust. So, you could try to keep it and to check all the other elements... Moreover, you will gain in comsumption. despite the accelerations of my 250 ETZ, I am capable of consumming less than 4,5 liter/100km (excuse me I am French, I am not comfortable with gallons and miles when I am not fast. Otherwise, I am around 4,5 l/100 in riding at 100/110 km/h...

All the mods I implemented on my ETZ are described there below (I have last started to adapt a reed box from Huqsvarna in order to increase the torque). Even if my engine is entirely new, you can make sure that what is described there is efficient. I am sure something is wrong on your engine either on the ignition, or arount the air filter and its cover, or on the carburetor's needle... Or both...

http://strv.pagesperso-orange.fr/motodesign/UKETZ.htm

[kokkiklhs]

Hi, I have the same problem with my 251, no torque at all below 4000rpm, but with my original exhaust set... my local mechanic says that it must be jammed by carbon, and advised me to take it for a couple of long easy-going highway rides, but I saw no improvement after all... it still is DEAD slow (especially with 2 persons) at low rpm and has pathetic acceleration... after that, it suddenly transforms to another bike... I discussed with another (older) 251 rider at my area and he said that this is how 251s are, under normal circumstances! I find this a bit odd, and I suspect that there might be another problem, except the exhaust...
Any suggestions?
P.S. Someone told me that it is possible to fit an ETZ250 exhaust+neck on the 251 for better performance, but my (experienced MZ specialist) mechanic says that this cannot be done due to different dimensions, and I would have to replace front wheel with 17'' one in such a case...

[claude]

Hello. I agree, the torque is not the strength of the 250 ETZ but there are some means to get more torque : increasing the compression rate, polishing the ports, adding an intake reed, and mainly, increasing the ignition advance (very efficient on a 2 stroke engine).
I've got a real improvment with may be 27° ignition advance (the guenuine one is 22°, described in the owner manual as a maximum to never exceed !)... Of course, it is bad for the engine to get a to big ignition advance so, in August, I will implement a programmable ignition system that enables to get a very big advance under 4000rpm and to decrease it regularly afterward, to get around 20° or less at 5200rpm (maximum torque speed, for cruising with a low engine temperature). And in parallel, I am working on a reed box to fit the 250 ETZ cylinder without any modifications on it. All the details of that on this page of my website:

http://strv.pagesperso-orange.fr/motodesign/UKETZ.htm

You have a photo of the reed box I am working on. If you want details to get a programmable ignition for 250 MZ, I can tell you the address of the french manufacturer that modify ignitech system to fit every motorcycle, including MZ.

Sure that I will get a stronger torque at 3000rpm... And a lower consumption

[claude]

Hello,
A piece of information relating this famous expansion chamber exhaust : I saw on a German website, may be the maker's one, that this exhaust is expect to get +1 HP. I don-t know at what speed but I guess it is just above the maximum power engine speed, somewhere around 6000 rpm.

[thomaskwscott]

Hi Guys,

I'm ashamed that i never let you know what happened!! I fitted the standard exhaust and the difference was amazing and instant. The torque is there even when 2 up! I have noticed a drop in fuel economy though....

[difflock]

the drop in economy is most likely due to the different exhaust characteristics....


BUT, is the standard exhaust you've fitted new or second hand?

if its second hand, it might just be a bit clogged up.....