NIBBI 28 carb for CSC TT250....YES!!

[Goob]

Hey all. I just installed a NIBBI 28 Kehein PE clone. This is the BEST carb for a CG250! I have had a KOSO Kehein PWK30 clone (previous owner installed), and a Mikuni VM26-606 that I installed in place to try to get better fuel mileage. The -606 was much better than the PWK, but the main issue for both was placement of the Pilot Jet screw. Both were obstucted by the frame, as they were on the left side. THe NIBBI PE28 has both the Pilot screw and the idle screw on the right side, so fully accessible. Also, throttle response and overall performance is much better than either the PWK or the -606. I used the stock 40 pilot (have other sizes on order), an used the spare 118 Main in place of the stock 115. This seems to work very well at 5280 ft. I may change the Pilot, as I am only 1 1/8 turns out. But it starts, idles, and runs GREAT. Orion Motorsports is putting these as stock on all of their RXB250's. These are now real OHC 250 cc bikes, so the carb should be plenty for our CG250/229 cc bkes. I have the aftermarket exhaust and UNI filter; otherwise stock The -606 is going to go on my RXB150.

[JerryHawk250]

The PE28 is a good match for a stock CG or CB 250. A 30mm carb is a better match for engines that the head has been ported to flow more air. Bigger is not always better. On a stock engine the PE30 and pwk30 is a pain to tune idle mixture.

[mtiberio]

What manifold with this carb?

[Thebrozzanator]

Ok so what about a 28mm nibbi pwk? Air filter aftermarket exhaust. Nothing else engine wise. Is this too small considering I have the vm26 mikuni 30mm clone on there right now? Just curious because I bought one for another bike I won't be receiving for another month. I would love to test this out on the Brozz if it is compatible.

[JerryHawk250]

Originally Posted by Thebrozzanator

Ok so what about a 28mm nibbi pwk? Air filter aftermarket exhaust. Nothing else engine wise. Is this too small considering I have the vm26 mikuni 30mm clone on there right now? Just curious because I bought one for another bike I won't be receiving for another month. I would love to test this out on the Brozz if it is compatible.

The PWK28 and PE28 are both smooth bore carbs. They are a true 28mm all the way through. If you look at your vm26 mikuni 30mm carb you will notice that the bore narrows down towards the slide so it's not a true 30mm bore all the way through.

[mtiberio]

FWIW, my friend has multiple land speed records using 250cc pushrod Aermacchi singles. I asked him what size carb they came with stock. He said 28mm.

[Thebrozzanator]

Nice I will definitely compare the two. I feel the vm26 fakuni is just not enough for the mods I have. It's very easy to tune and get it running prime but I just feel like there can be a little more. Updates will come once it's delivered. I'll probably have to order a different manifold but I'll see if I can run the one I bought for the other bike. Thanks for the feedback!

[Mr. Fixit]

I can’t speak on the PE28 or the PWK28 but I just got a PE30 tuned about 2:30 this morning, I’ve been tuning on it since Friday evening. It is on a 2020 Brozz with stock head and internals, I removed the air box, adjusted the valves, NGK plug, changed oil, removed catalytic converters, gutted and rerouted the exhaust inside the can, and cut the sharp radius header pipe off and welded a different one on that was more gradual. The factory pipe closes up to less than half an inch on the inside where it turns back.
My point being the Nibbi 30mm carb is a pain to get tuned properly. It takes a lot of time and even more patience.

[Mr. Fixit]

But now that it’s tuned right it is a great carburetor, immediate throttle response, it makes great power from half throttle and up, and the idle is smooth.

[Goob]

Originally Posted by Mr. Fixit

I can’t speak on the PE28 or the PWK28 but I just got a PE30 tuned about 2:30 this morning, I’ve been tuning on it since Friday evening. It is on a 2020 Brozz with stock head and internals, I removed the air box, adjusted the valves, NGK plug, changed oil, removed catalytic converters, gutted and rerouted the exhaust inside the can, and cut the sharp radius header pipe off and welded a different one on that was more gradual. The factory pipe closes up to less than half an inch on the inside where it turns back.
My point being the Nibbi 30mm carb is a pain to get tuned properly. It takes a lot of time and even more patience.

Mr. Fixit..I wrote some more to you on another post, but my experience was the opposite. It took 15 minutes tops. Stock 40 pilot, 118 Main, no needle clip adjustment. I installed, adjusted the pilot screw, adjusted the idle. Done. I am at 5280 ft, so I expected more tuning would be required. Just goes to show...you never know.

[Goob]

Originally Posted by mtiberio

What manifold with this carb?

This is the one I bought for a spare...what's on there is from PO. There are many out there on Ebay or Amazon, price ranges from $7-15 or so.

This one seems to be of good quality.

https://www.ebay.com/itm/30mm-Carbur...72.m2749.l2649

[Goob]

Originally Posted by JerryHawk250

The PE28 is a good match for a stock CG or CB 250. A 30mm carb is a better match for engines that the head has been ported to flow more air. Bigger is not always better. On a stock engine the PE30 and pwk30 is a pain to tune idle mixture.

This was my experience. The previous owner had put on a KOSO PWK30 clone. It just always seemed to be too large. Can't explain why, it ran well, but no matter what I jetted it never was what I wanted...just a feeling.

I went the other way with a Mikuni VM26-606, which ran great but I lost some zip and top speed. Also, the pilot screw was blocked by the frame, so no running adjustments possible.

I decided on the NIBBI PE28 because I saw the review of the NIBBI by MegaDan and that Orion has changed to using it on their new RXB250's as stock. A bonus is that the idle and pilot screws are on the right side, so fully accessible for adjustment while running.

I think it is a perfect match with just the aftermarket exhaust as the only other modification. Got my zip back.

The VM26-606 is going on my RXB150 this weekend to replace the VM26 Flange mount. This is for the same reason JerryHawk250 mentions regarding a smooth bore carb. I don't think the -606 is actually a smooth bore, but it is better than the VM26 Flange mount with more restriction visible and a butterfly choke.

[Goob]

Originally Posted by Thebrozzanator

Ok so what about a 28mm nibbi pwk? Air filter aftermarket exhaust. Nothing else engine wise. Is this too small considering I have the vm26 mikuni 30mm clone on there right now? Just curious because I bought one for another bike I won't be receiving for another month. I would love to test this out on the Brozz if it is compatible.

Someone else may have a better reply, but I think the PWK, being a flat slide, may have better flow and more instant throttle response. This is why they are popular with serious dirt bike folks.

[Thebrozzanator]

Thanks I literally just ordered the nibbi PE 28mm. I noticed the same thing you mentioned about the PWK. Impossible to tune due to the location of the idle and mixture screw. Although I would love the PWK for better throttle response. So I'll be waiting for the PE and save the PWK for the 2021 KP mini I have coming at the end of the month. FINGERS CROSSED. Also I am at different elevation but I think I will start off with your suggestions and see if I can improve the tune from there.

[Goob]

Originally Posted by Thebrozzanator

Thanks I literally just ordered the nibbi PE 28mm. I noticed the same thing you mentioned about the PWK. Impossible to tune due to the location of the idle and mixture screw. Although I would love the PWK for better throttle response. So I'll be waiting for the PE and save the PWK for the 2021 KP mini I have coming at the end of the month. FINGERS CROSSED. Also I am at different elevation but I think I will start off with your suggestions and see if I can improve the tune from there.

Yeah, I should have waited to order extra jets and tried stock from the get-go. Mike at Jetsrus.com told me to do that, but I am a bit anal about having everything on hand that I may need.

I think you will be very happy with the PE28. I am loving it. Just makes the whole riding experience better.

A note for you on a PWK clone. Mine was a KOSO PWK30 (as described to me by the PO who bought it), but the Kehein main jet that actually fits it is for a Kehein PWK28. The difference is that the 30 is a hex jet, while the 28 is a smaller (length-wise) jet that screws in with a flat blade screw driver. Once I found this out, I ordered parts for the Kehein PWK28 from jetsrus.com and everything fit.

I found this same issue with the main jets I got for the PE. When I ordered the "real" PE28 mains, I got the hex jets. Lucky for me I had the correct ones from my second order for the PWK, which are the same jet part #.