Difference between 17 and 21 hp 251 ETZ's

[teemu]

Does anybody know what is the difference between these two models? I think the 17 hp model was made for domestic use in the DDR but how to tell the difference?
I bought my bike from Vietnam in the early 90's and it doesn't have the oil pump so I have to presume it is also on 17 hp. I coild use the missing 4 hp.

[manumensa]

Hello teemu!

The 21 HP. was the "standart" model and the 17 HP. was "de Luxe model" or "export model" .

For DDR and socialist orbit countries MZ made the "standart" model -no electronic ignition, no oilpump, no rev. counter . German RFA - 17 because 21 HP. MZ had law problems there- and capitalist countries MZ exported "de Luxe" model, the only way for sell in a competitive market.

My opinion you own a 251 "standart" 21 HP., the 4 HP. more must be a diferent cylinder port timing.

Best Regards,

Manuel

[teemu]

Thanks Manuel!

My bike doesn't have the oil pump but is equipped with the rev. counter. Also it has the later model plastic rearfender. The main problem with it has been that it has never been so "powerful" that I could have used the fifth gear. Only in long downhill decents and when the wind and sun are behind me. Never on flat road or towards wind.
I drove about 100,000 km before taking it to pieces and had it bored to to second oversize at once. Maybe the solution would be to get a cylinder somewhere.
I hear a theory that the power reduction is done by the exhaust, don't really know how.

[manumensa]

Hello!

I read the bike "Operating Instructions" book and can see in the picture standart model haven´t rev. counter - and have metalic rear mudguard- but really never saw ETZ 251 bike or photo without rev. counter.

My friends have ETZ 250 and 251 "de Luxe" -17 HP.-and the bikes run OK, of course not the Moto Guzzi or Harley D. torque . They travel in highway long mileage no problem in fifth , 800-1,000 meter over the sea level and drink fuel aprox. 7 liters/100 Kilometers.
Theoretically your bike must work better.

The 251 standart don´t have opposite cone - cone sport bike exhaust always the labyrinth cigar type. Exhaust bridle? I think not.
Generally the power come from the cylinder port timing (also carburation, etc...),, more engine safety and duration than up the compression.


Saludos, Manuel.

[teemu]

Hello
Never saw a MZ without the rev. counter either. Propably no one wanted it.
I must check the carburator and it's settings as it is the BVF. It might be leaking or something. Or then I should change it to Bing or something else.