Nibbi PEZ28 on 2024 CSC TT250

[Bill Hilly]

This is a follow up to my post earlier today. The Nibbi PEZ is not a PZ30 clone, but it is made as a slightly more direct replacement for the PZ30. Basically the PE28FL, and the PEZ look the same, but the PEZ has about 45-46 mm O.D. breather side, and the PE28FL has about a 49mm. I think, (but don't know for sure) the PEZ has a different needle. I don't have a PE28FL around anymore to compare with, BUT I have noticed the needle on my PEZ is very sharp, and thin , and has no taper for about the first 3/4" or so. Any jet bigger than a 115 slides way down the needle. A 120 slides right down it . I realize that's probably why I had to lower the needle so far when I had my hotter motor , and was running a larger main. I don't think the needle in the PEZ is going to be ideal with larger jetting. These are pictures of the needle, and the needle with a 120 main on it. A 115 will not slide over it.http://http://

[ughmas]

I have a PE28FL and I have faced similar initial tune/jet challenges with it. I'm betting its almost the exactly the same except the OD of the inlet side. I can take some measurements if you are curious. I just took the bike out since its starting to cool down to a reasonable riding temp, I was about to take a fresh crack at tuning it. following along with your experience and will let you know what I end up with

[superjocko]

For what it's worth, I tried a 40 and a 38 before settling on a 35 pilot. I had to have the pilot air screw out farther than I'd care to with the bigger pilot jets, and could also not achieve as clean a transition to the needle when the bigger pilots were in the carb. With the 35 pilot jet, and the needle clip in the second groove from the top (next to leanest needle position), I run my pilot air screw anywhere from 3/4 to 1-1/4 turns, depending on the elevation that I'm riding at. I just tune the pilot air screw for best idle and throttle response in a manner very similar to that in the already posted youtube video.
I'm using the same natural aluminum colored body Nibbi 28mm flange-type carb that I believe the OP is. However, my engine has the Motocult stage 3 kit installed, so your results may vary.

[ughmas]

Originally Posted by superjocko

For what it's worth, I tried a 40 and a 38 before settling on a 35 pilot. I had to have the pilot air screw out farther than I'd care to with the bigger pilot jets, and could also not achieve as clean a transition to the needle when the bigger pilots were in the carb. With the 35 pilot jet, and the needle clip in the second groove from the top (next to leanest needle position), I run my pilot air screw anywhere from 3/4 to 1-1/4 turns, depending on the elevation that I'm riding at. I just tune the pilot air screw for best idle and throttle response in a manner very similar to that in the already posted youtube video.
I'm using the same natural aluminum colored body Nibbi 28mm flange-type carb that I believe the OP is. However, my engine has the Motocult stage 3 kit installed, so your results may vary.

Thanks for this, that was my planned next move when I pull the bowl and needle out - I had not tried leaning out the needle (had been trying to get it to be happy on stock 3 position and 4 position richer) Will report with how it goes. what are you running for main?

[Sdmfjon]

I've learned an interesting pattern with the needle and air screw.

Changing the needle position forces me to change the air screw.

With a 40 idle jet.

Needle position 4 = 3 turns out to achieve highest idle.
Needle position 3 = 2 1/2 turns out
Needle position 2 = 2 turns out.

* At needle position 2 I have to use the choke to start the bike cold, even on a very hot day. At needle 3 I don't really need the choke.*

Also does everyone's bike decel pop? No matter what tuning i do, it decel pops very steadily. No emissions systems on my bike either / no exhaust leaks.

[Sdmfjon]

But anyways. Yup not right.

At this point neither tunes have been correct.

115 main and 38 pilot. Needle 2 (best tune)

Too rich, flat acceleration, back soot from exhaust. Idle was nice but coming off idle sucked. Sometimes it would even just shut off if I tried to rev match, decel popping. Bike wouldn't start without choke no matter outside temperature.

112 main and 40 pilot needle 2 (best tune)

Need choke to start, decel pops the same. Idle is really nice, coming off idle is really good. I can rev match just fine. Still sounds rich but now it bogs when I transition between half and full throttle. The engine makes more power at 3/4 throttle (and sounds better) then at full throttle.

Things I have given up on.
- crack throttle bog. Never gonna go away.
- decel pop. Sounds the same since day one.

*I know it's been said before to look into a different needle but at this point I don't want to throw another variable into the mix. I really just want this bike to start up, run good and be a reliable ride around the city.

[bigdano711]

I was experiencing the same issue where it wanted choke to start, even after sitting in 80 degree heat for hours. Now, you KNOW that's just wrong. I started coming down on my main jet and got to my lowest, 100, and now she starts fine without choke on a warm day.


I noticed in the Nibbi manual I posted that the main jet and needle work together from like half throttle to WOT. Just something else to consider.

[Sdmfjon]

Update. Getting really close now.

Seems like this carb wants a rich needle. The tuning manual has this carb at position 4 stock. All the others are position 3. So I said to myself. I'm gonna leave the needle at 4 and adjust the pilot jet to it. I ended up with a 35 pilot jet at 1 and 1/4 turns out.

I'm posting a video of it at idle. Please tell me if this sounds too rich or lean.

Current tune.

Stock bike with emissions removed and Nibbi PEZ28 carb fitted.

Airscrew 1 1/4
Pilot jet 35
Needle position 4
Main jet 112

https://youtube.com/shorts/KfyKM3t8Bxk?feature=shared

[superjocko]

Originally Posted by ughmas

Thanks for this, that was my planned next move when I pull the bowl and needle out - I had not tried leaning out the needle (had been trying to get it to be happy on stock 3 position and 4 position richer) Will report with how it goes. what are you running for main?

I have a 115 main jet.

[superjocko]

Originally Posted by Sdmfjon

I've learned an interesting pattern with the needle and air screw.

Changing the needle position forces me to change the air screw.

With a 40 idle jet.

Needle position 4 = 3 turns out to achieve highest idle.
Needle position 3 = 2 1/2 turns out
Needle position 2 = 2 turns out.

* At needle position 2 I have to use the choke to start the bike cold, even on a very hot day. At needle 3 I don't really need the choke.*

Also does everyone's bike decel pop? No matter what tuning i do, it decel pops very steadily. No emissions systems on my bike either / no exhaust leaks.

My bike decel pops. I still have the air injection installed, so it's probably going to no matter what. I don't find it particularly objectionable.

[bigdano711]

Originally Posted by Sdmfjon

Update. Getting really close now.

Seems like this carb wants a rich needle. The tuning manual has this carb at position 4 stock. All the others are position 3. So I said to myself. I'm gonna leave the needle at 4 and adjust the pilot jet to it. I ended up with a 35 pilot jet at 1 and 1/4 turns out.

I'm posting a video of it at idle. Please tell me if this sounds too rich or lean.

Current tune.

Stock bike with emissions removed and Nibbi PEZ28 carb fitted.

Airscrew 1 1/4
Pilot jet 35
Needle position 4
Main jet 112

https://youtube.com/shorts/KfyKM3t8Bxk?feature=shared

Sounds good to me. I like your airscrew position. If you like it, you can do a plug chop to read how lean/rich it is. Or just put in a new plug and check it at next oil change. I go with the latter.

[Sdmfjon]

Update: getting dialed in now.

The mid range was still too rich. I got a chance to put some miles on it today. I changed the needle to position 3. That really helped.

At this point I'm going to do a wot plug chop to verify the 112 main is correct.

Stock bike with emissions removed and Nibbi PEZ28 carb fitted.

Air screw 1 1/8
Idle jet 35
Needle position 3
Main jet 112.

[Sdmfjon]

Originally Posted by bigdano711

Take picture of needle. I will do the same since I yanked it out of my Nibbi PE28FL. I will lay it next to a Keihin needle and you will see obvious differences. The best solution for me in the mid was a Keihin JJH. Didn't I JUST type this recently......?


I got this needle/jet kit off Amazon. I can find the link if anyone is interested. I had no idea they were Keihin clones. You can see in the macro pic that the entire adjustment range is lowered, yet there is significant overlap. I tried every position on the Nibbi needle, with no jet changes, and could not discern any kind of appreciable difference from one setting to the other. Maybe yours will be different as there is a significant altitude drop from me to you. I read on some other forums about guys having really good luck with the JJH and, since I had one to try, I figured what the heck. I got immediate feedback, letting me know my pilot jet was too large. Adjusted that back down to 38 and slowly worked my main jet down as it was too large. I am now at 38 pilot, middle position (I think) on the JJH needle and a 105 main. The main is still slightly rich, but I think it works. That Nibbi needle is just too fat.

The needle in the PEZ28 is different from the PE28FL. The PEZ needle is shorter.

[Sdmfjon]

Update. I put some miles on it with the new settings. Major improvement in the low end.

Something is still not right. As of now I'm fairly certain idle up to 1/2 throttle is set.

From 3/4 to WOT now I'm having some issues.

When I had the needle at position 4 I noticed the bike made more power at 3/4 throttle then wot.
Now with the needle at position 3 the bike feels like it's doing this. ↑↓↑↓↑↓

I have a 110 and a 115 jet. My gut tells me to try the 115 first (for safety of the motor) then try the 110

[Sdmfjon]

Well everyone. Back to square one.

Yesterday I noticed the carb drain overflow line was wet. I took it off and dried it out. Took it for a ride today and guess what. The drain overflow is wet again.

So I'm guessing my too rich problem is the float not adjust properly. Or ( more than likely ) I bent the float tab when changing out the jets so many times.
Either way, this is F@#$ed