TS 250 PWK carb

[Kruh]

I fitted a PWK 30 mm carb on my TS. I've ridden the bike with this carb for over 3000 km and I'm pretty happy with it.
Specificaly this is a OKO replica.

You are probably interested in the settings and mounting, I sure was when I looking around but didn't find a whole lot.

My settings:
Pilot jet: 42
Main jet: 116 (Dellorto jet); 122 Keihin equivalent
+power jet (not sure which size)
-needle in the middle notch, its the same that came with the carb (no writing on it)

I mounted it by cutting the original flange, specifically just the part where the original carbs inserts to. Than I just filed until a got a smooth and round flange. Onto which i put the included rubber coupler.
Turned out great. Imo, better than the original. Should seal better and minimize vibrations to the carb.





Being that this is a cheap replica I did run into a issue.
The thread on the float bowl and drain screw is not made well. So its easy to crossthread the drain screw and strip the thread. Which is exactly what I did.
Good news is that these carbs are very cheap. For the price of a bowl and drain bolt I could just as well buy a complete carb.

I really like this version of the carb:



The only issue is that those verions are available only in 33 mm (smallest size)

So, my question to you is:
Is a 33 mm carb too big for a stock TS 250?

If I go with that carb, I would enlarge the intake manifold from the stock 30 mm to 33 mm. So the manifold is not a bottleneck.
My goal with this isn't necessarily to get more power. Although a slight bump wouldn't hurt.

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[Kruh]

The bike smokes a bit under heavy acceleration. Should be normal to some extent, but it seems a bit too much to me.
A more useful fact; when I ride, on the open road, above 100 kmh there is visible smoke in the mirror but not that much. That is riding at about 1/2 throttle. When I go up to 3/4 or more there is quite a bit of smoke.

Would seem that the mixture is to rich in the high end. But the bike isn't sputtery or "4 stroking". I tried a smaller main jet. The smallest was a 106. Also tried 112 and 118 without the power jet. No major difference. Curently I'm at 116 with the power jet with which it runs well but, as I said it is smokey.

Was even thinking about the crankshaft seal (cluch side) being bad.
But normal riding aorund town and country roads, its all good. I do not see any smoke. Maybe something uphill, but generally it fine.
At idle it also fine.

I'm running 2% premix with fully synthetic oil (Castrol power 1 racing). I assume then it would smoke less than mineral oils.

Is this a somewhat normal thing for MZ. It is a big cc 2 stroke after all. I'm just wondering how a good MZ 250 runs at higher load since most of my experience is with smaller cc 2 strokes.

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[Kruh]

Yeah, it is quite possible there is also corrosion the clutch side of the crank. Which would cause wear on the seal.
I did check the gearbox vent (the oil cap), the hole is fine.

I'll try smaller jets again and give it a more thorough testing. Just to make sure. Otherwise I'll be cleaning the crank and replacing the seal for good measure.

The bike does feel good and the plug is fine. Its dry without much carbon. The color might be just a litlle bit on the rich side, but that litlle bit could also be down to other factors (as in your attachments)
Also, I didn't do a full throttle plug chop so this is just the general running state.



Also, thank you for all your help

[Kruh]

I got another carb. This time I went with a ZSDTRP PWK30.

Same as any other PWK, but with a few differences; it has a thumbscrew cap, no powerjet and fuel inlet on the left.

Comparing it to my OKO carb, this one is definetly better quality.
Finish is nice and smooth, everything fits nicely, the slide is better quality (the chrome plating), it also has less play in the body of the carb, the ventury is polishe all the way thru, threads fit more tightly.
Especially the float bowl cap. On the OKO the thread is bad: loose fit and crooked, strips easily.
It could just be that I got a bad one. But the ZSDTRP feel better in every way.


The setup now is:
- Pilot jet: 40
- Air screw: 2.5 turns out
- Main jet: 125, a 120 might be better
- no power jet
- needle in the 2nd notch from top, its the same that came with the carb (no writing on it)



The jets are hex, just like the original Keihin. It also come with a second needle, 3 main jets and 2 pilot (maybe it should've been also 3, but I go only 2).
The needles look the same (same taper). But haven't measured them.












How it looks on the bike. I replaced the choke with a cable one to make it more like the original

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[Kruh]

Well, I don't care too much abot the look of the carb on the bike. The cable does complicate things. But I like how the TS choke lever looks; it fills the space on the handlebar and makes it look more sophisticated i guess.

I also thought it would have an added benefit of finer control of the choke, insted of just on or off. But in practice it makes no difference. It might be more useful in cold conditions.

It runs better now than with the OKO. Its snappier overall and more stable at idle. The idle was a bit troubling to tune on the oko.
After it warms up there is no visible smoke. With the OKO, it would visibly smoke even at idle.
I done only a few short rides, so we'll see how it behaves long term. Especially on faster roads; with more load.

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[Kruh]

Regarding the extra needle that comes with the ZSDTRP carb. I measured both needles and they are exactly the same, other than the material. What difference does it make, I have no idea.
I also checked the OKO needle and it is the same.


I managed to get a proper ride now.
The jetting was the same as in the previous post, except I raised the needle to the middle (3rd notch from top), just like I used on the OKO.
Turns out it too rich. So I put in a smaller main jet and droped the needle.

The setup now is:
- Pilot jet: 40
- Air screw: 2.5 turns out
- Main jet: 115
- needle: 2nd notch from top

It is interesting that it prefers smaller jets than the OKO did.
It runs very well now. It is very responsive and it feels like it has more power than it did with the OKO.
Also, now it starts first kick every time.

I do have one issue with it and its the same I had with the OKO.
Sometimes when I stop the idle stays high for a bit, until it settles. Once it settles I can rev and it drops normally.
This would indicate to me that its lean, but when I turnes the airscrew in a bit, it was too rich (slugish on the throttle).
The throttle cable doesn't seem to be the cause either.

Any possible culprit, other than just me not tuning it correctly?

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[Kruh]

I checked the taper as well. It is exactly the same.

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[Kruh]

After about 3000 km of riding with the ZSDTRP carb, everything is doing great.
There is wear on the slide - some of the chrome has dissapeared. Perhaps too much?
As far as I know, these slides do wear on the bottom edges, even on the original carbs, but the middle portion probably not that much.

ZSDTRP slide left, OKO slide right. (the milage on the OKO is slightly less)



Onto jetting:
I lowered the needle all the way during these summer days and rode like that for a while. But it was a bit lean.
So I went from a 115 to a 120 main jet and raised the needle by one notch (2nd from top). Now there was an issue of stuttering at around 1/4 throtlle.
Compared the throttle valve cutaways on both carbs, and the OKO had a slightly larger one. So I tried that slide to lean the mixture at that throttle position. And it was an improvement.
So I copied that on the other slide, because the OKO slide has a lot more play in the body of the carb. (I couldn't find any specific dimensions on the original keihin slide cutaways)
Went from 3.9-4 mm (don't remember excatly) to 4.2 mm.




Spark plug:




The setup now is:
- Pilot jet: the same as before
- Main jet: 120
- needle: 2nd notch from top

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