Nibbi PEZ28 on 2024 CSC TT250

[bigdano711]

Doesn't get much better than that. Did the stumble go away? What manual are you referring to? The one that came from CSC with the bike or a Nibbi manual? Here's what I got for Nibbi:

[Sdmfjon]

Update.

It's too rich. But like a hair too rich in the midrange. Random stumble coming off idle. Sounds fat like a tractor.

Going to try two things.

First. Raise the needle clip from position 3 to 2.

If that is unfavorable I'm going to try the factory combo from the PE28FL. This would lower the main jet to 112 and change the needle clip to position 4.

My manual looks different than that one. I have the factory settings for the "PE**FL" lineup and the clamp on lineup.

[Sdmfjon]

Update. That worked. No stumbling, no gassy smell.

I still can't crack throttle from idle to anything 1/2 or beyond. If I bring the bike off idle it's fair game. Oh well. I don't want to spend 300 dollars on a really nice genuine pumper carb like my hondas have.

Final tune for now.

Stock bike. Emissions removed and a Nibbi PEZ28 fitted.

38 idle jet
Needle position 2
Air screw 1 1/2
Main jet 115.

[dirtbkr188]

Strictly a suggestion, you only need a screwdriver and some time - try turning the air screw IN a 1/4-turn (to richen the pilot circuit), ride the bike and see if the off-idle hesitation lessens. If so, try another 1/4-turn and test ride, until you think the hesitation is gone. If you get to being only a 1/2-turn from seated, then you might want to bump the pilot up to a #40.


Just my 2¢...

[Sdmfjon]

I started with the 40. It made me have to put the air screw almost 3 turns out to achieve highest idle.

The 38 puts me dead between 1 1/4 and 1 1/2.

[red2003]

Originally Posted by dirtbkr188

Strictly a suggestion, you only need a screwdriver and some time - try turning the air screw IN a 1/4-turn (to richen the pilot circuit), ride the bike and see if the off-idle hesitation lessens. If so, try another 1/4-turn and test ride, until you think the hesitation is gone. If you get to being only a 1/2-turn from seated, then you might want to bump the pilot up to a #40.


Just my 2¢...

1/4 turn on the air screw of a Nibbi is HUGE. I am running a PE28 and 1/16 turn on the air screw creates or removes an off idle stumble. Luckily, like you said, on a Nibbi it's easy to fuss with. I'm sure the OP could get the off idle stumble out with a few minutes of fine tuning.

[Zapkin]

I have the nibbi on my 2022 hawk 250 and using this video:

solved all of my carb situations and the bike runs great. check it out.

[Sdmfjon]

Update. Still not right.

I think the 115 is too rich and causing issues.

I'm going to go from 115 to 112. Which I'm pretty sure is going to throw everything else off.

[flopsweat]

Oof. Makes me glad I nixed the idea of putting in a new carb, this sounds quite frustrating.

[Sdmfjon]

Originally Posted by flopsweat

Oof. Makes me glad I nixed the idea of putting in a new carb, this sounds quite frustrating.

I didn't want to. I was forced too. The back story is I live at the beach. The stock was way too lean, bike would barely run.

The stock carbs should have had a 38 108 combo. The one I received had a 35 102 combo. After a few phone calls with CSC, it was determined that CSC could not get 38 jets for the Keima. So, they sent me the jet kit. The 40 idle jet didn't work but the 112 main did. The bike was very finicky. It really needed the correct idle jet.

[Sdmfjon]

New tune. Feels better ish. Need to have some real world experience over the next few days. It definitely accepts crack throttle better. Not perfect but better.

Air screw 2 1/2 turns out
Idle jet 40
Needle position 3
Main jet 112

[Sdmfjon]

I would like to point out that I am not running a Nibbi PE28 or a or a Nibbi PE28FL.

I am running a Nibbi PEZ28. It is a clone of the pz30. It is a direct bolt on for the Hawks / TT250. No fuel tank clearance issues, no throttle cable to short issues, and you can install/ remove it without having to bring the intake manifold with it.

The PEZ comes stock with a 40 / 108 combo. But includes a 38 idle and 102, 105, 108, 110 main jets.

The PEZ uses the very common yamakato / keihin / the jets everyone knows and loves.

The air screw is on the side next to the idle speed screw. Very easy to tinker with.

[Bill Hilly]

I opted for the PEZ28 when I had the hotter motor on my Hawk. I chose it over the PE28FL, because it was cheaper, AND the fact that I had a fairly new Nibbi pod filter that I was running on a PZ30 stock type, but properly jetted carb. I had a hard time getting the roll off from full throttle hiccup tuned out of the PEZ28. I tried jets , and never got it completely out. I ended up having to lower my needle. I can't remember if it was one, or two notches from center. The bike ran great, and the power increase was really noticable on the hotter
motor . It took throttle great, but would still occasionally hiccup just slightly when I rolled off wide open throttle quickly. Like I say I chose the carb out of saving money . I ordered it from AliExpress, because it was winter, and I could wait a little while for shipping. I don't know if all the PEZ28 have the extremely sharp needle, but the one I bought did. I don't remember the needle from the PE28FL that I had on my TBR7 being as sharp. I have a feeling that my PEZ28 would be a better carb with a different needle.

[bigdano711]

Originally Posted by Sdmfjon

New tune. Feels better ish. Need to have some real world experience over the next few days. It definitely accepts crack throttle better. Not perfect but better.

Air screw 2 1/2 turns out
Idle jet 40
Needle position 3
Main jet 112

2 1/2 turns out is too much. It's telling you to change the pilot jet. Do you know if turning it out richens or leans? I believe I found that the Nibbi manual had that backwards, adding to my frustration. Anyway, you want to be as close to 1 1/2 as you can get.


Good luck. Remember, there are different needles to try, too. lol

[bigdano711]

Originally Posted by Sdmfjon

Update. That worked. No stumbling, no gassy smell.

I still can't crack throttle from idle to anything 1/2 or beyond. If I bring the bike off idle it's fair game. Oh well. I don't want to spend 300 dollars on a really nice genuine pumper carb like my hondas have.

Final tune for now.

Stock bike. Emissions removed and a Nibbi PEZ28 fitted.

38 idle jet
Needle position 2
Air screw 1 1/2
Main jet 115.

Go back to this tune. You're trying to get it to operate like a 2 stroke and I am telling you, man, it AIN'T gonna happen. As for idle, this was your best setup. It's going to die when you crack the throttle too wide. The sooner you accept this, the less hair you will lose. lol


You're going to get so frustrated you'll buy that $300 pumper carb. Just go ahead and buy it already.