'20 RXB250L - NC250 Motor Swap [Build Thread]

[Ursa_Adv]

Tire bead has been reseated. Front axle greased and torqued.

The bike is now resting on her own tires (and side stand) for the first time since disassembly. As soon as I get a break in the weather, I will take her for the first test ride.

[Ursa_Adv]

While waiting for the weather to break I have been staring at this brake line:







The stock line was extremely short and I always found myself "pulling" it when turning. Decided to go with a longer line and used this 150cm brake line I found on amazon:
https://www.amazon.com/Motorcycle-Re.../dp/B07MT7Y262

At the time I was just stoked to have a brake line that wasn't too short, but now I'm staring at it as it pours rain.....Annnnnnnddddd I hate it. I ordered a shorter line (140cm) this time. I will test it out and report back.

In other news, I think the bike is running a bit lean and has been stalling out while idling. I am going to check the plugs today and adjust as needed. If it is lean and not just a bad A/F adjustment I will probably move up to a 35 (currently at a 32).

I also need to fix the tachometer wire to the coil as its a bit precarious and losing the coil mid ride is not something I want to deal with. Then its fixing the speed sensor bracket as there is no location to mount the button magnets. So I'll have to just use magnet brake disc bolts and extend the sensor bracket to reach them.

[Ursa_Adv]

I also drained the radiators and engine yesterday as the temps keep dipping near freezing. Replaced the distilled water with Engine Ice. Should keep things safer as the PNW moves into winter temps. Last thing I needed was a cracked block because I was being lazy.

[Ursa_Adv]

Put in an iridium plug (NGK 7385 CR7EIX) after pulling the stock plug. Stock plug was sooty and black. So I may have been wrong on my assumption I was running lean at idle. Might be running a tad rich. I'll play around with the tuning and report back.

Built a makeshift speed sensor bracket to position the sensor over the bolts so I can use it properly.





It isn't the prettiest, but it'll work for now. I might pop a weld on it just make it a single piece of metal. That way I don't have the thought of the link coming loose in the back of my mind.

[Ursa_Adv]

I gave up on trying to get the tach to work. I can't source where the wire from the gauges needs to connect. I've tried a number of places, but no dice. No signal.

When I was closing everything back up, my starter switch has decided to just stop working. Bike won't fire when I press the starter button. So now I am chasing down this electrical gremlin. Great start to the weekend.

[Ursa_Adv]

Electrical gremlin fixed. At this point I have replaced every stock connector on the engine harness save the CDI and Rectifier.

[Ursa_Adv]

Working on iteration 2 of the exhaust.




Much better clearances and air gaps. I'll probably take it monday to be welded and then mount it up.

Magnet bolts for the speedo are on the way and I am thinking about getting a new master cylinder/brake lever. The I have is a cheap amazon folding lever and it always feels spongy. Even after repeated bleeds. Always has like 10+mm of play before engagement.

[Ursa_Adv]

Finding a welder willing to do motorcycle exhaust work has once again proven to be a pain. Most of the shops that do the work are considerable distance away and with the holiday coming up, the likelihood of me getting this before December is looking slim.

I am about one buzzed amazon purchase away from just welding it myself.

[zero_dgz]

Do it...


I've very successfully welded plenty of exhausts just with my dinkum Harbor Freight 120v flux wire welder. It works fine. For thinner bike exhausts you have to use the "sheet metal technique" of giving it short zaps and allowing it to cool a little before the next one so you don't blow through it.


My only other advice with the HF welder is to ignore the sticker on the inside of the lid that recommends the wire speed and voltage. Mine seems a bit optimistic and the suggested settings are too low for correct penetration and weld bead formation on any material I've tried it on. Maybe they use the same sticker for the 240v model, who knows.


Invest in a can of anti-spatter spray for flux wire welding. Hose down the areas around your weld and the little spatter balls just brush right off leaving the weld looking nice and professional. Ish.


The rest of my welding is decidedly farm-grade, so I haven't quite invested in a TIG welder. Yet.

[Ursa_Adv]

While waiting on welding, I went back to searching for information about how to get the tach working and I found this on an Amazon review for the same gauges but a different seller:

"The tach did not work when wired to the low voltage (12v) side of the coil. I tried wrapping wire around the spark plug as well to no avail. I then spliced it to the positive side of the pickup coil that senses engine TDC and the tach began working. Make sure you set it to 2 cylinder because it will pick up 2 pulses per power stroke."

Now this is what we've got:



Which wire would be considered the "positive" side of the coil?

[XLsior]

If its just a mild steel exhaust then DIY with a gasless fluxcore mig will be a great place to start and learn. Great skill to have and super useful bit of kit for running repairs around the house.

think I paid $200 aussie dollars for my 160amp and a decent face shield.

That being said I got some practice in fixing my front stairs runs and making a rocket stove for scrap 4" box section before making my custom exhaust.

There is also gasless stainless steel wire too...but it will never look as nice as TIG.

A grinder and a lick of high temp paint or a glass wrap and it might even pass the cosmetic scrutiny.

Im using my gasless mig as it also has stick weld option so now making a swing out tire rack for my 4WD van...

[Ursa_Adv]

Originally Posted by XLsior

If its just a mild steel exhaust then DIY with a gasless fluxcore mig will be a great place to start and learn. Great skill to have and super useful bit of kit for running repairs around the house.

The exhaust is a stainless steel. I keep looking at 110 amp stick welder that has decent reviews and a good record of people using it to wield stainless.

[Ursa_Adv]

I found a welder for the exhaust. Dropping it off tomorrow.

I may have also solved the tachometer issues, but I won't know until I get the exhaust back. I'll post up the solution if I do find it. As this gauge is pretty nice...once you figure out how to wire and set the parameters correctly (did not come with documentation).

[Ursa_Adv]

Iteration 2 of the exhaust is back and this will hold me over for the time being. I might redesign it one more time later on down the line, but we're in a rideable state now.

3 items are left to be addressed:

• Wrap header to lower temps due to proximity to cooling pipes. A reduction in excess heat will also keep the gas tank from takin on additional head soak.

• Install some kind of fan/temp gauge setup.

• Figure out this tach issue.

On a side note: After three weeks of not touching the bike, turned on the choke and she fired right up. Two cranks and slight throttle.

Nothing really there, just felt good to know she'll start for me each time.

[Ursa_Adv]

The "new" exhaust:





The air gap for the water pump is good but I may re route that bottom house just for the extra clearance. I also removed the kickstarter because it was basically sitting on the pipe. Its in my saddlebags though. So if I ever need it, I can slap it on.