ETZ 250 carb 30N2-5 tuning

[turbinee]

Hi all,
my name is George and I am from Bulgaria. I have an ETZ 250 that looks really good but does not run
I managed with the help of the German MZ forum to get spark and adjust braker timing and actually start the engine, but now I have a problem with the carb. I need info on how to make the basic settings so I can mount the carb and do fine tuning on the running engine.
At the begging the carb would not let any fuel get to the cylinder, so it was probably due to rust and junk that sat too long in it. I bought a NOS carb body (30N2-5) and installed all new jets and float and needle, but I cannot find info on how to set up the adjustment screws on the body nor the float height. I see there are general recommendations for setting float height on the MZ 150 carb on the web, but nothing for the MZ 250 carb. Also I think I read somewhere that the adjustment screws need to be bottomed out and then returned 4 turns, but do I do that for both screws? I made a picture with the adjustments in question, please have a look and let me know what you think.
Any help is much appreciated

[Blurredman]

Hello George. Welcome.

Firstly, the middle screw is for the height of the slide. This essentially is controling the idle speed. This will actually be non-standard on this type of carb in the sense that it entirely matters what position the main needle is and where you like the idle to be set (Haynes and official service manuals say 1,200-1,300rpm.

The screw on the right is the idle/pilot adjustment which will adjust the quality/quantity of the fuel/idle and part throttle. This indeed should not be excessive- 4 turns from in is quite excessive however in variation to what the manuals say, which is normally about 1-2 turns - adjustment is dependent on again the requirement.

If the bike can idle (although poorly) then firstly adjust the pilot jet screw first. You are looking to find the heighest idle speed, and then adjust the idle back down to the appropriate 1200.
If the bike cannot idle, then start the bike and pull the throttle slightly so that it just opens the slide and then adjust the screw clockwise slowly until the bike will idle better without your help.

It is best to just use the screw settings in the manual as a base line. Obviously carbs wear and adjustment over time can sometimes be required.

So.. Coming to the proceedures. In my signature you will see my link to my FTP which will have both the original service manual and the Haynes manual which would also give you float height requirement.


ftp://blurredmanswebsite.ddns.net/Vehic ... Documents/

[turbinee]

thank you Blurredman for sharing the manuals, I will go through them. Can you tell me; I see the needle has four notches, is there are default position on which to set the needle? Also seems the shims to accommodate the needle have to spread, but this doesn't look right to me. please see my picture and tell me is this the way the needle fit in the shims?

[turbinee]

Thanks Blurredman, all the info is in the ETZ250 official service manual! Thanks for sharing it with me.
I adjusted the float and tomorrow will try to start the bike.
If other MZ owners need the info the settings for the float on the 30N2-5 carb are:
- closed float with fully depressed valve spring 27mm +1mm
- closed float with valve spring not depressed 30mm +1mm
- open float 33mm +1mm.
The partial-load needle is set between 3rd to 5th notch on the shims, 5th notch is for initial brake-in only.

The Haynes manual has slightly different lengths for the float adjustment, but I think they are more "universal" and not 100% accurate. The Original service manual is better I think.

[Blurredman]

I agree. Which is why I always look up the official manual first. However, any pictures that the haynes manual has can 'sometimes' be useful. But I have found outright wrong information in the Haynes sometimes. For example the pilot jet screw initial setting is quite way off from the original manual.

Anyway, yes- the needle has 5 slots, however only 4 slots are actually 'usable'. I haven't seen it explicity mentioned, but everywhere I see on the Internet uses the lower clip as the 'actual' slot position, the upper one just rides and is there for stability and keep the needle in place I suppose.

So yes, your needle is also in the correct middle position.

However, this is something you may need to mess with- I myself find that the needle is better in 1 notch richer setting for my ETZ250. After many years I have given up trying to find out so I just keep it as is. The 1 notch richer does allow the bike increased torque in lower RPM and I think it makes the bike more docile and nicer to ride. You might get more smoke, but I never noticed any appreciable increase in fuel consumption. It must be so minor.

Anyway. It can be a long process to tune a carburettor to the engine properly. I wish you all the best !

[turbinee]

thank you.

I will mount the carb and see what will happen. I will post the results.

[Blurredman]

Any luck, Turbinee?

[turbinee]

Pulled out the bike yesterday and got it started today ☺️

So I replaced the carb with NOS carb and new jets. It starts very easy, but runs at around 1.8 2000 rpm.

Will try the recommended above settings and report again tomorrow.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[turbinee]

Yes, it is new old stock, sorry no nitrous oxide

So I adjusted the carb per above settings and sitting in a place the engine runs sweet, just occasional hiccup, but low stable rpm's. However I drove today and there are problems; it will run out of gas and it will try to stall. Have to stop rev the engine and continue. I am thinking either the filter in the tank or the filter in the petcock is blocked.

Could this be the problem, or could it be something with the jets inside the carb? I put all new jets and needle, but don't remember if they were german or imitation.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[turbinee]

Thanks for the advice, went ahead and ordered new petcock assembly, should be here by Friday and will try again

Other thing I noticed is when I engage first gear the rpm's drop. Is this normal or I need to adjust the cable tension? The gears engage really easy and the going from stop is very nice.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.