OKO carb for ETZ251

[alexxx]

I just cannot get rid of the surging and poor tickover, no air leaks, carb gaskets ok
Got to be mainly down to the carburation.
I put the bike in the shed and did not even MOT it this year as it was too annoying anytime the throttle was closed so will try a new technology carb.
The surging really spoils this good bike, were they like that from new?

Regards

[Andy_C]

Alexxx.

Sorry to hear that you have parked the bike up - as you say they are good little bikes.

Just one suggestion, earlier this year my bike went through a phase of not wanting to tick over, surging like mad and generally running very poor.

After much head scratching and messing around, the problem turmed out to be electrical - I found that a lot of the push on terminals were very loose, particularly around the rectifier & regulator box.

I pulled them all off and closed them up with a pair of pliers before re fitting them - no problems ever since, it has been running better than ever.

Also have found through experirnce that if the battery is not holding charge it can have a similar effect.

Might be worth a look if you feel inclined.

[alexxx]

Thanks Andy,

Will check over the electrics as you suggest.
I fitted a new Yuasa 9amp battery and the bike has electronic ign as standard, it could be a combination of lots of small issues.
Happy to fit a new carb to see if I can improve over the original design.

Regards

[DAVID THOMPSON]

I found that a lot of the push on terminals were very loose,

my 660 traveller has this problem and the rt 125 has had some loose ones also

Dave

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[parrbd]

I have found surging is cured by running a rich pilot setting on all the types of two strokes that I have owned.

[Blurredman]

Also, I'm not certain you can actually do this with the standard BVF, where you set the idle using a bypass circuit, rather than by the lift of the throttle valve, as is more common.

Interestingly, only the very last production of the BVF used the bypass circuit, the 30n3-1. This was only standard on 251 machines. Previous MZ motorcycles used the throttle valve lift adjustment for idle setting. And before that, as I recall- the idle adjsutment was on a nut adjustment on the throttle tube- Which is still found on the later models, but I think mainly adapted for the use of adjusting throttle lightness.

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[alexxx]

Thanks folks,

Helpful as always.
My bike does have the 30n3-1 carb.
Happy to try swapping it out, does not cost very much and if no difference I can use the carb in another bike sometime.
Will post on here once I have fitted and tested it.

Regards

[Andy_C]

My ETZ 250 is running a 30-n3-1 carb.

As I said in an earlier posting

"when I first had my ETZ is used to buck and stutter and was very unpleasant on the overrun, it is pretty good these days. I spent a lot of time fiddling with carb settings - mine has a BVF and it is happiest with 2.5 turns out on the airscrew, and 4 turns out on the bypass screw."

It is pretty sensitive to settings, air screw in too much and the pickup is awful, bypass screw too far in and low speed running is poor - seems to 4 stroke a bit.

It is a juggling act, try using my settings as a base and go from there, but only adjust 1 screw at a time and in small increments 1/4 of a turn is good.

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[Blurredman]

And there you were saying that originality doesn't mean best.

I have no experience of Bing carburettors, but I've read alot into carburettor swaps on these bikes.

But out of the original line available with these bikes, I still think the BVF 30N3-1 has got to be the best BVF carb..

You mention performance, but alot of people find fuel consumption to be better on other carbs than with the originals. Did you notice any mpg increase- or even decrease? If it decrease, is this potentially because you were testing the bike to the limits and were feeling throttle happy? What if you rode it like a normal person on a commute?


Perhaps what you should do is map out a track route. only about 10-20 miles of a nice circular road. One with some city traffic, some with country lanes, maybe a part with a nice place to do a full throttle run. Do the route several times find out what gear you need to be in or where the rpm's are at specific intervals... Then swap carbs.. Can the new carb seem to climb that hill a little better than before? Did I previously need to change down to be able to take that corner without labouring the engine?

You could even fill up the tank for each carb and measure consumption...


Or maybe that's just way too much effort

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