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Discussion Starter · #1 · (Edited)
I have been doing a few updates on facebook, but I figured I should do it here also.


I will post as much as a can to help anyone that wants to undertake the swap, but be warned it isn't for the faint of heart. I will require some of your own fabrication, and wiring knowledge.
IMHO a reliable big bore is a better option since the inclined layout of the CBR, and the position of the throttle body (TB) doesn't fit very well in our frames.

My fix around the TB is to build a frame around it, like other motorcycles do. Mine is crude and I am giving up weight for insurance that the modified frame will hold.


Ok, on some info for anyone that would want to continue:
Sprocket and Chain
The CBR front sprocket is 520 and the grom rear is 420
You can change the front to a 428 (stronger that 420) and change the rear also
OR
You can change the rear sprocket to a 520, and run a 520 chain.
The only 520 sprockets that I have found to fit the grom bolt pattern is JT Sprockets: Catalogue
The one that I bought is a 32 tooth and will be geared just slightly lower with a 140/70/12 rear tire.
4th gear @ 8500 rpm Stock CBR = 101.2 KPH
4th gear @ 8500 rpm mentioned set up on grom = 95.9 KPH
1982-1982 Honda CM250 C JT SPROCKET 32 TOOTH, Manufacturer: JT SPROCKET, Manufacturer Part Number: JTR279.32-AD, Stock Photo - Actual parts may vary.: Amazon.co.uk: Car & Motorbike
Said sprocket on grom
Tire Bicycle part Automotive tire Auto part Groupset

Wiring

Grom Diagram

CBR250R Diagram
Plan Technical drawing Text Drawing Diagram


Text Font Design Diagram


For the CBR harness (not shown on any diagram) there is a Pink anti-theft wire that is for the ignition switch that will need a zener diode that taps into a "hot" wire. ( I have not resolved this yet)

Fuel pump *update*250r clip works with the Grom fuel pump, as is. I had previously said the the fuel pump polarity was reversed but I was wrong about that.

Right Handlebar
Text Line Diagram Parallel Plot


Left Handlebar
Text Line Parallel Diagram Plot

*I forgot the two wires for the clutch switch.
The Grom wires on are G/Y and G/R
The cbrs are BL and BL going to one plug
There is another black wire in the loom but it goes with the horn on a separate plug.



Ok, I am tired for the night and I will update more later.
Here are some teasers

Radiator under rear fender
Engine Auto part Automotive engine part Vehicle Car
Auto part Automotive exterior Bumper Vehicle Engine
Auto part Engine Motor vehicle Vehicle Car
 

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I'll be posting my throttle body mods as soon as I get my 250r running- I'm thinking of separating the throttle body and injector mount so I can keep my throttle body on a 90 degree custom intake (stock frame backbone). I'm thinking a PCV will be a necessity for proper ride ability with this setup.
 

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Are you concerned about cooling since you have the radiator under the seat? I have no idea how much air passes through there or if you need airflow for that setup
 

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Note the electric FAN under there as well. I'm sure it'll potentially make for a hot seat but hopefully he's in a cooler climate and could use the warmth... ;)
 

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Discussion Starter · #14 ·
I live in Texas so cooler climate, hell no, I hate it.
The radiator is the factory CBR, so I was going to run it as it is and just monitor it. If it gets too warm I will remove the factory fan and install two higher cfm fans.
 

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And also set them to pull air rather through rather than push. Well, I guess in colder months a heated seat might not be detrimental, maybe a flip to reverse air flow. ;)

If it doesn't violate your moniker (user id for the kids), Where in Texas are you?
 
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