ETZ 125 carbs

[otb123]

Hello, new here...

I have acquired an ETZ125 which doesn't run particularly well (spluttered to a halt and made me push it up a hill!), fuel tank was rusted up and blocking the petcock badly (but seemed to run ok after cleaning this out), so I assumed it was this it... Anyway, have had the tank off and given it a really good clean removing the vast majority of the rust, also installed an inline filter... Ran about a pint of fuel through the petcock and didn't collect anything in the filter so am happy the fuel supply is now good...

Removed the carb and open it up, all the installed jets were as the Haynes manual with the exception of the main jet, the book specifies a 100, I have 115 fitted. The needle was badly worn/corroded, however with nothing to hand to replace anything I gave it a little clean and refitted...

Also to note, I went to inspect the air cleaner to see if it was fouled, only to find it missing! will get one ordered... And on a 5 min look the timing appears to be a little advanced (~3.5mm BTDC, the Haynes says 2.5mm). Also, pending the level in the oil tank going to down to make sure the pump works, there is a gallon of 50:1 in the tank not strait petrol.

Does anybody have any suggestion with what to target first? I have been looking to see if I can pick up an after market carb, however only see the 24N2 (presumably larger for the 150) carbs at reasonable prices (the one fitted to the bike is 22N2), however looks like I can get the jets specified in the haynes book for mine... Does any body have axperience of runing the 24N2 carb on the 125? or advice on how to jet it?

Any help suggestions etc greatly appreciated!

Kev

[Puffs]

Hi Kev & welcome!

Sounds like you're making all the right moves. Without air filter you will need a bigger main & a higher needle (or a worn needle...), have a look at the plug. Clean it & adjust it & have a look what colour it gets after running (pics in Haynes manual P.27). Of course best put an air filter in asap.

I cannot really advise on a carb for a 125, but please be aware that the jetting depends on the size of the bore; particularly the main, needle & needle guide. I don't think you should expect the jetting that is standard for the 22mm carb to also work well in a 24mm carb. Although it's just 2mm bigger, you may find some changes are required (particularly a slightly bigger main). Quite likely the standard 24mm jetting will be working better, also on the 125. Also: what's the ID of your manifold? Can you enlarge it to 24mm? (And will the 24mm carb fit on it?) Just a thought: what happens with the mixture during the last few mm of throttle travel, if the main restriction to flow is actually downstream of the carb (as you would have if you put a 24mm carb on a 22mm inlet manifold)? Anyway, be prepared for having to find your optimal jetting, and after installing a proper air filter.

But do you really need a new carb? Things that wear on a carb are: throttle valve & throttle body, needle & guide, and the float valve & pin. If throttle valve & body are still good enough, the rest you can probably find.

On the other hand, I'm sure the engine can be made to run fine on any suitable carburettor. It may just require optimisation of the jetting.

The other thing I suggest is to take the head off, at some stage, to have a look at the cylinder bore. Particularly if it has been run without air filter for a long time. How does it sound?

[otb123]

When going well it sounds good, tends to bog down when wide open so will revert back down to the specified main (with air filter, so prob should anyway), I'm pretty sure that the wear (although it looks more like a a chemical thing (corrosion), could equally be abrasion from particles in the rusty tank) on the needle has been leading to random fueling... I've ordered an air filter, new needle, the specified 100 main jet and a new set of points as when I timed it up the existing were pretty pitted...

I wasn't stuck on a new carb, more that for the ~£30, if all the jetting was going to be pretty much there, it may have been easier / quicker, although now I'll wait until I have an air filter back in and new points before trying to set the fuel up...

How much arching is generally accepted as normal? I'm getting what look like pretty low energy sparks that seem to originate from the cam side contact and appear to move out away from the engine rather that higher energy arching across the contacts.

K

[Puffs]

Bogging down at wide open might be because of too rich a mixture - does it miss beats (is it four-stroking)?

You can sand the points to get rid of pitting. Use a piece of fine (240 - 400) sandpaper, folded in the middle so that it sands on either side.

It might be too late to make it to the same order, but in cases like this, replacing the condenser is also an easy & cheap try. With age & use, condensers can also become a bit unreliable. And the condenser is there to prevent severe pitting, so if the points have that, there might be an issue with the condenser.

The biggest spark it should draw: I don't know. Not sure if that is specified anywhere, for this bike. The spark plug gap is 0.6mm, so I'd guess a few mm at least.

If you see wear on the piston (through exhaust or inlet) it will at least partly be due to dust coming through the inlet. But some marking with use is common, IMO.

[otb123]

Luckily I have ordered a new condenser as well, but am seriously considering going electronic... Either way I need to wait for the new air filter and needle before setting anything up so am stuck waiting for the postman

I'll report back with how I get on...

[otb123]

So, air filer now fitted and carb restored the book settings (100 main and new needle)... Running is much better!

I will do some plug chops at some and see what you guys think...

I currently have the needle clip at 3 from top which the book says is for running in but want to see how overly rich this actually is, also I have 50:1 in the tank and the autolub still all connected so more oil than normal, which would lean out the petrol some?

In light of the above, during an hours run last night I am only getting 50ish out of it, does this sound normal for the 125? Once I get the oil pump off and on just premix at least I'll know the oil ratio is correct...

[otb123]

Attached is a pic of the plug after some general running about i.e. a mix of all throttle positions... the plug was not new and the insulator was covered in black prior to this from how the bike was running prior to carb clean, re-jet and timing being set right...

Does anyone see anything wrong here? I'll do some controlled runs at some point with new plugs...

[otb123]

Well, I had a go at some plug chops, however pretty sure the results are no good due the run not being long enough...

Attached is picture of the plugs, the one on the left is at ~50% throttle and the one on the right wide open, however the bike did idle during the run down (the lights were on and I just clicked the key once, to the ignition still on position! )...

As I say I don't think the runs were long enough and were likely less than 60 seconds, need another go I think, I'd be very surprised if the 50% was as lean as it looks as the needle is already one position higher than the book says.

Plugs are B8HS.

What do you guys think..?

Cheers

[Puffs]

Well, I think you ruined 2 excellent brand spanking new plugs - why on earth did you take the thread off?

Anyway, you can only read a plug after it has done quite some miles. No, 60 seconds is not enough. And with 1:50 in the tank + the oil pump working, it will be a rather greasy 1:25, so the one in the pic above looks quite normal to me.

If at full throttle, when you look in the mirror, do you see a haze of blue smoke behind you? Then the pump works.

I do not know what the top speed of an ETZ125 is, but I wouldn't be surprised if it maxes out at 55MPH (it also depends on your size & posture). I believe they are just 10HP.

Anyway, if it runs well, I'd just make some miles with it & lean-up the fuel with normal petrol, of course assuming you have said smoke.

When you started with both tanks full, you can estimate the pump's mixing ratio from the volumes added. Initially it will not be very accurate, but the longer you keep a record, the more accurate it will get. I'm actually doing the same thing at the moment.

[otb123]

I have also taken a look a the crown with endoscope, there is carbon deposit all over to edge, so I've raised the needle by one and only had a short run but seems maybe a little better acceleration, certainly no worse...

Regarding smoke, while flat out I'm not seeing massive amounts which I had expected to (oil pump and premix together)? The oil in the premix is a low smoke semi-synth (no idea what's in the oil tank other than its red) so maybe that's why, I have been monitoring the level in the autolub tank and it is going down so its doing something... Either way I'll be removing the pump, need to make a blanking plate up over the next few days then see how I go when I actually know* what oil ratio I'm burning.

I now have the lower needle clip 4 notches from the top and the plug is a nice chocolate brown colour...

[Puffs]

On the issue of the mixing ratio of the oil pump; I've kept a record of oil use & petrol use and for my '89 ETZ251 I calculate an average mixing ratio of 1:50.2.

Within the measurement accuracy that's equal to the factory specification of 1:50.