1975 cb 125 s2 engine swap to a 2007 crf 150r

[littleredrocket33]

Hey guys!
My name is Daniel and i have a 1975 cb125 s2 that ive had for a few years and ive decided to repower it with a 2007 cbr 150r motor which i ordered today! my questions are : 1: has anyone ever heard of anyone doing this swap before? 2: are the engine mounts in the same location (im sure im not that lucky and will have to build brackets and do some finagaling) 3: does anyone know the rough gas mileage that one of these motors might get in this bike? and 4: pray for me. ill post some pics soon of the bike and check back up in a day or so. Thanks everyone! Dan

 

[Sonreir]

1.) No
2.) I'd put money on, "No", but that would also be the answer I'd give if you'd asked if you were going to win the lottery
3.) Depending on how you ride, somewhere in the 80 mpg range
4.) We'll do even better, we'll offer advice as you post your progress

 

[Maritime]

Nice idea, are you getting the throttle bodie, injector and ECU too? I believe that motor will be fuel injected and you will need the CBR ignition switch and key maybe too incase it is chipped. Other then that What Sonrier said above. Cool little bike, it should rip with the modern engine.

 

[SONICJK]

1975 cb 125 s2 engine swap to a 2007 crf 150r

Should be a blast with a real engine in it.
I'd wager the engine swap will be pretty fab heavy, as there is no cradle in the frame so you'll have to redo the front engine mount for the new engine.

 

[littleredrocket33]

Ok... So i tore down the 125 engine and wiring harness and i now have the new engine that came in the mail and i think im in good shape for installing the 150r motor on the 125 frame!!! the back motor mounts are almost identical and the front one is slightly different but not too bad. i will have to create a top motor mount for it if i really want to use the original top motor mount but its not looking bad guys! i have the original cdi and a original carb in the mail i will post pics when i get it lined up and mounted. wish me luck! Dan

 

[littleredrocket33]

BIRD is the word! so i mounted the engine today and to all who would have ever guessed i did it without changing the stock motor mounts!!! so looks like i did win the lottery! i am super happy with how little work i really had to do! makes my life a little easier. ill post pics tomorrow and let you guys get a look at how it is going so far. the only thing that i will have to relocate is the swingarm. it will have to go down about 2 inches on the frame due to the fact that it is in the line of where the chain needs to be. i was thinking about using a crf 150r swingarm and changing the suspension, and rear brake to a disk and what not. any thoughts on this? thanks, Dan