CB250N cafe racer with supercharger

B

busse

New Member
I will do a thread about my CB250N cafe build. In 2016 i bought a broken CB250N that I build a cafe racer from and it was finish in the spring of 2017 and I drow it that summer. But in the beginning of the summer of 2018 I bought a Triumph Thruxton so the Honda was not used much, so what to do with the bike? Than I got an idea to mount a supercharger on it wich was a totaly stupid idea.

I started to find information about superchargers when I dont have any experience of turbon and superchargers. I figure out that an Aisin AMR300 might would work and as this was a cafe racer I want to have the carburator before the supercharger and draw tru the carb instead of blow tru.

After alot of searching I found a supercharger and the build colud start. I decibel to place the supercharger on the left side of the engine and took the power to the supercharger from the flywheel but I but that was the things that I do that winter. In The spring of 2019 I crashed with my KLR650 and broke my knee and an other things get in between so there was not much done on the bike.

When I continue on the build I brass solder the Inlet from exhaust pipes and did a popoff valve and in the fall of 2020 I got the bike running and a first test runt was taken. I got boost pressure but the engine lean out under acceleration but I seems to work.

I'm from Sweden so my english could be a bit wrong ;)

To continue.....

The object I started with
https://postimg.cc/sGBbvcvN][/url]

Mounting the supercharger
https://postimg.cc/2qLgWf5B][/url]

Building the inlet
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The drivebelt to the supercharger
https://postimg.cc/Y4vm0rDF][/url]

The bike reade for test
https://postimg.cc/rRKLsXkn][/url]
 
Un the winter of 2020, 2021 I did a belt guard for the drive belt and a new rear fender with place for the electronics and some other minor changes. So in the spring of 2022 I continue with test rides when the bike lean out under acceleration.

I tested a Mikuni HSR42 but it was to big, so I tried with Mikuni VM32, Keihin FCR33, CR29 but I still got the problem. Then on a swedish forum someone gave a suggestion to ute CV carbs when back in the days SU was used with draw thr turbos. Then I realized that I got a 29 mm CV carb as stock carb from the bike så I split the bridge and put on the stock carb.

I only drow about 1 km the first run with the CV carb, the bike runed lean but over the whole range. I went home and put in some big jets and now I got the bike running, not good but it was drivable. Next step was testning jets and needle height but I still got lean out under acceleration. To my helt I got a Innovate wide band lambda so I could see afr ratio.

Next thing was to mount a Mikuni acceleratorpump to the Keihin CV carb, this with jetting make the bike better but not good.

In the winter 2021-2022 when I know that the bike was running I started to make some finish on the bike, new stanless steel exhaust and stanless steel was welded.

To be continue...

https://postimg.cc/s1rZTXSP][/url]

https://postimg.cc/yWQ7ttYy][/url]

https://postimg.cc/VJ0KZqSW][/url]

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Next step to get the bike more old looking was wire wheel, the rear wheel from some Honda CB250 K-model was easy to fit and the chain had the right offset I only had to do a new spacer on the right side to get the wheel in the swingarm.

The front wheel was taken from a Kawasaki I think it was from Z200 and it was more work to get it in place, spacers and I had to modify the front axle when the speedometer gearing was on the other side. A speedometer cable from a Boatian moped did fit the meter and the drivning unit. The brake rotor was special ordern from ISR to fix with the Kawasaki front whee and the stock caliper and fork. I like the 18" front wheel better and looks better I have keep the tyres narrow to get an older look.

More carb tubing was done in the summer of 2023, I grinded the throttle needle so I got more fuel in the midrange and this helpt a bit to get the bike running better, next step was to make restrictorplates with diffrerent hole sizes to put inside the throttle so slow down the lift under acceleration to prevent lean out and now did the bike run pretty well but eas lean out when you turn off the trottle. The last thing I did with the carb was to modifyed the slow jet that att pressed to the carb. I pull it out and drillinng it up with a 0.6 mm drill and thred the lover part to use Bing jets to adjust the fuel.

The last thing on the bike was cleaning up the instruments, I replaced the boost guage and the AFR meter and made new white dials to the speedometer and tachometer.

With all of this I will say that the bike is finished. We went to a car and bike show in Oulo Finland and I did not expect anything but to my suprise I got a "special award" prize.

https://postimg.cc/XZmbwkYV][/url]

https://postimg.cc/2VGNHDS9][/url]

https://postimg.cc/VJ5sn6WW][/url]

https://postimg.cc/TKSd96kM][/url]

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https://postimg.cc/H81C9G2Y][/url]
 
Is this the same engine as the Honda CM200T? Would love to hear the sound of the bike with the supercharger if you have a video. Great work
 
You are seriously nuts in the best possible way. It's always good to see someone try something different. I liked the SuperDream. My brother in law had one years ago. Fun bike but not a lot of character but smooth and handled fine.

Congratulations on the award. All that hard work deserves some recognition. EFI might be a way to move forwards with the fueling issues.
 
Thank you all that you like this totaly stupid project.

I don't know if the CB200T has the same engine platform as the CB250N.

I don't think EFI would be easy but alot easier than a carburator but I want the bike to be oldschool with draw tru supercharger and a carb. The build I work on now is getting EFI, it's a CB250N with turbo and the plan is to make it in late seventies early eighties race style inspired by Honda RS1000 and Suzuki XR69 but smaller.

Here's some videos of the bike.


 
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