'20 RXB250L - NC250 Motor Swap [Build Thread]

[zero_dgz]

Originally Posted by China Rider 27

The NC450 conversion may be what it takes to get the Dual Sport many crave!

Brawndo: The Swingarm Mutilator (tm). It's got horsepower. It's what dual sport riders crave.

[China Rider 27]

I might have to get me a Brozz swingarm before I stuff one in my HAWK frame! Ha, ha, ha... CG strong, ride Hard!

[Rashid]

Originally Posted by Ursa_Adv

I lucked out on the tank. The KTM style tank that Orion used let me swap in the larger Acerbis 5.3 gallon tank which gave me more than enough room to fit the radiators in. The larger problem was the front forks and the exhaust impacting them.

We decided on a slightly swept back position for the radiators. This gave us enough clearance on all fronts.

What carb and jetting did you end up going with on your swap? I've got a few laying around in the garage of varying sizes. (Nibbi 26mm, 32mm Nibbi style that came with the engine, and a 32mm Flat-slide Mikuni clone).

I've seen a lot of SSR riders swap in the FCR or dump that money on MxRevival's Lectron setup. Most seem to point towards a 34mm being the sweet spot, but I'd love your opinion, knowing you've done a swap like this before.

Indeed 34mm is the best option for NC250 until you do the big bore kit. I have used Keihin PWK 34 clone and it is working perfectly fine though I have to jet it as per my conditions. I am attaching the picture of the carb.

Pilot: 33
Needle: clip in 2nd position from top
Main: 135

Now it starts fine, idles fine, and no bog anywhere in any throttle range. In my case tank was the major problem, got it fabricated and then the radiators' shrouds would not cover the extra-long husky radiators so got them fabricated as well.

[Rashid]

The only regret I have is, I should have gone for Big Bore Kit when I was rebuilding the motor. I am not sure why I decided to go with the stock kit.

Now around 2000 miles on the build, I am thinking to do the big bore kit but confused on which one to choose. 82mm (283cc tried and tested by multiple riders here on CR) or the 84mm (298cc which may affect the clutch as well as well as require carb change and an extra fan on radiators)

[Ursa_Adv]

Originally Posted by Rashid

Indeed 34mm is the best option for NC250 until you do the big bore kit. I have used Keihin PWK 34 clone and it is working perfectly fine though I have to jet it as per my conditions. I am attaching the picture of the carb.

Pilot: 33
Needle: clip in 2nd position from top
Main: 135

Now it starts fine, idles fine, and no bog anywhere in any throttle range. In my case tank was the major problem, got it fabricated and then the radiators' shrouds would not cover the extra-long husky radiators so got them fabricated as well.

Awesome! Thank you for that. I will keep that handy.

Did you go the CRF250R route for the exhaust? I've been trying to figure out what year header will work with the NC250.

[Rashid]

Originally Posted by Ursa_Adv

Awesome! Thank you for that. I will keep that handy.

Did you go the CRF250R route for the exhaust? I've been trying to figure out what year header will work with the NC250.

I had a full system for CRF 230 lying with me for a long time. It is a clone as well from Aliexpress, my fabricator spent like 30 min to adjust the header to make it work with NC 250 exhaust port.

The muffler is a bit loud but is not restrictive at all which is my first preference.

[Ursa_Adv]

Originally Posted by Rashid

I had a full system for CRF 230 lying with me for a long time. It is a clone as well from Aliexpress, my fabricator spent like 30 min to adjust the header to make it work with NC 250 exhaust port.

The muffler is a bit loud but is not restrictive at all which is my first preference.

That actually works out. I am rather fond of my XR Only's exhaust system that I had on the 233cc motor.

[Ursa_Adv]

I removed a majority of the "extra" wire in the lighting harness. Even isolating only the lighting, horn, switch, and power sources there is still a lot of wire.

Going to try to finish up the harness this week as it's finally warm enough to work in the garage again.

[XLsior]

From my experience the green single common earth wire that services the front cluster and back to the main ground is not heavy enough gauge and should be replaced.

I had my loom frizzle a number of times and attribute it to this single green thin strand of wire.

I ended up replacing the main ground and 12v ignition feed with I think 15amp auto twin core.

[Ursa_Adv]

Lighting harness is complete. Ran through tests on everything this morning. It all works. Now I just have to wait until I get the frame back so I make sure my wire lengths are correct and tie the positive wire into the hot wire on the ignition.

Don't need the lights bleeding the battery dry when the bike is off.

[Ursa_Adv]

Bench tested the new speedometer today. It came with zero wiring information. Luckily some digging around the web got me in the right ballpark.

Happy that I got it to power on. Tested indicator lights, speed sensor, and the gear indicator. All checked out.

Funny thing is I believe these are the speedometers they are now installing standard on the 2021 and up RXBs.

[zero_dgz]

Originally Posted by Ursa_Adv

Funny thing is I believe these are the speedometers they are now installing standard on the 2021 and up RXBs.

I'm pretty sure you're right. That looks suspiciously identical to the one that came on my bike.

[Rashid]

Originally Posted by Ursa_Adv

Bench tested the new speedometer today. It came with zero wiring information. Luckily some digging around the web got me in the right ballpark.

Happy that I got it to power on. Tested indicator lights, speed sensor, and the gear indicator. All checked out.

Funny thing is I believe these are the speedometers they are now installing standard on the 2021 and up RXBs.

I have the exact same one on my bike as well. Works fine and the speed reading is pretty accurate as well. Which speed sensor have you got with it?

I have only one issue with it, on high RPMs, when the bike vibrates, the digits on speedo starts flashing. I am thinking to add some vibration dampers to the speedo mount.

[Ursa_Adv]

Originally Posted by Rashid

I have the exact same one on my bike as well. Works fine and the speed reading is pretty accurate as well. Which speed sensor have you got with it?

I have only one issue with it, on high RPMs, when the bike vibrates, the digits on speedo starts flashing. I am thinking to add some vibration dampers to the speedo mount.

It came with the magnet speed sensor and two button magnets to stick on the rotor. I might just pick up some Koso magnetic brake rotor bolts, as the rotors don't really anywhere to put the button magnets.

I actually had that same thought when I was looking at the bracket last night. I will take your experience in stride and throw some rubber grommets in there to give it a little cushion.

Any chance I could bug you for a picture of the "settings" page on your cluster (pulse, tire size, cylinders, etc)? I think I have mine setup correctly, but if yours working accurately...I'd love to steal your settings. lol

[Ursa_Adv]

Spoke with the fabricator on Tuesday. We talked at length about the amount of time it has taken him to get all the frame work done. I appreciate that he was honest about it (this type of project isn't what keeps him in business), but I still lament the fact I haven't had my bike since December.

I have been promised that I'll have everything back within the next week. I am not holding my breath, but I am hopeful.

It means I will spend most of the summer running the wiring, testing the engine, and slowly re-assembling the bike.

Fingers crossed, I have a meaningful update in the next few days.