ETZ251 won't cruise smoothly

[alexxx]

Checked the carb, it is a 30n 3-1 for sure but it only has one adjustment screw a large one to the right rear, the other one you mention may be under a blanking cap.
I had the needle in the middle position for the last run, checked the plug, very clean so I thought it was running weak and moved the needle to the fourth position to richen it up a bit (this is where it was when I first got the bike).
Just been on a run, it does seem smoother and pulls better from lower down, cruising seemed improved and the over run had a less surging but still some.
I am no sure how to get the tickover a bit higher, the charging light comes on sometimes when the tickover drops a bit.
I can't find any good position for the large adjustment screw (air feed?) that lifts the revs high enough, I have got it ticking over about 1100 but can't get it higher.
Will check the plug tomorrow to see how it looks.
Got to say..I am very impressed with the smoothness of the suspension, took it over some very rough badly patched roads ( some Edinburgh roads are like the third world) it felt smooth and stable, and still handles very well around corners, if this had a torquey engine it would make a great off road bike (apart from the daft position of the clutch cable entry) really happy with this bike

[Andy_C]

Yep the air screw probably still has the bung covering it - easy enough to pry out.

I have the manual on the 30N3-1 and I can email it to you if you like - just send me a mail with your email address on it and I'll send it.

Think the manual says 2.5 turns out for the air screw and 4 for the Bypass screw - the big one.

Once the engine is up to temperature turn the air screw IN until it reaches peak revs - do it slowly to give the engine time to respond, once you reach peak revs back it OUT a 1/4 of a turn.

If the revs are too high turn the bypass screw IN - again slowly to let the engine respond, screwing it out makes it rev faster.

Mine is very sensitive to screw settings as little as 1/8 of a turn of either screw can make a big difference, I also find that having a faster tickover than recommended - mine is nearer 2000 RPM.

Suspension on mine is pretty hard even with the rear dampers on the weakest setting - if you want a more torque go for a 301 conversion, I had a 301 for a short time and it was amazing how much more low down power it produced.

These bikes are fun bikes and I have no plans of getting rid of mine for the foreseeable.

[Blurredman]

Hi..

I know this is years since it was active, but did the OP find a resolution to this?

I'm currently experiencing exactly the same problem on my 251 which I've had for years without this problem.. so far as I can make out, I don't think mine is carb related but electrical but not sure.

[Puffs]

Zombie thread & the OP hasn't been seen in a year. PM?

I vaguely remember he was looking at the exhaust & also trying another carb, but cannot remember if he ever solved it.

[alexxx]

Not used my MZ in a while.
The surging was unbearable and I had other bikes to use.
Going to have another try at getting this bike to run smoothly, I bought a new Mikuni vm30 for another bike but it was not a neat fit so can try on the MZ.
Before that I wil try a new OKO carb I have, used them successfully on another bike so very hopeful it will help the MZ run better.
The OKO is much smaller than the Mikuni, that should make fitting a bit easier, there will be mods to make to the inlet manifold I guess.
I've now got a strobe light so can finally set the timing accurately.
I'll need to get it out for an MOT so I can road test the bike, can't belive it is still too modern by 10 years to be mot exempt, they weren't modern when new

[Puffs]

Removed