Honda CBR300 engine swap into a CRF250L.

Discussion in 'Thumpers' started by Cuttlefish, Jan 7, 2017.

  1. Cuttlefish

    Cuttlefish Riding to disappear.

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    Just got a text from Gerard...."Starts and runs perfectly so far!" He plugged in the 300's stator cable to the 250l's harness as per above pics.
    Dropped off some bar risers, a pair of Renthals I had already, Pro taper pillow grips, USB power cable kit and a quiet insert for the FMF Q4 this morning.
    #41
  2. swimmer

    swimmer armchair asshole

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    So at this point the totality of modifications needed to swap the 250 with the 300 is one electrical connector?
    #42
  3. Cuttlefish

    Cuttlefish Riding to disappear.

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    Plus you need 300r throttle body and ecu.
    The engine came with a 14 tooth front sprocket on it too so now I have a spare.
    May need a new exhaust header gasket as there's a slight difference in header size.
    Pretty good so far.
    This is why I wanted to do this thread. If its nice and straightforward its great to have the information out there for others to utilise.
    #43
  4. DaBinChe

    DaBinChe Long timer

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    So with this 320cc build what was done about fueling? Was a EJK used?
    #44
  5. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    Technically the 300 engine will run just fine with the 250 throttle body but will be a little down on top end power simply from the size difference..
    #45
  6. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    Yes... My bike had an EJK when I bought it and I'm still using it
    #46
  7. Cuttlefish

    Cuttlefish Riding to disappear.

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    The crf300r/l has been road tested. Gerard took it for a spin on his bike test route and reckons it goes great. He went as far as to say he wants one. Running the 14/40 stock sprockets. With a bit of luck he'll be able to check the steering head bearings and re-grease or replace if necessary and he can get the parts tomorrow which will be Saturday here. Hopefully I can collect the bike tomorrow afternoon after work and then take it for a run up into the hills of the hinterland Sunday morning. That way I'll really get a good idea of the difference when I take it on some of my favourite twisty roads.
    #47
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  8. swimmer

    swimmer armchair asshole

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    Really cool that all seemed to go so smoothly.
    #48
  9. swimmer

    swimmer armchair asshole

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    So it looks like the new CRF250L/Rally come with a 38mm throttle body which is the same size as the 300. I am not knowledgeable about this stuff to know if there are any other difference that would make the '17 38mm TB a deficiency vs. the 300 TB.
    #49
  10. Andysrage

    Andysrage Been here awhile

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    The 2017 upgrades to CRF (larger throttle body, airbox, ECU programming) will possibly make these the "easiest" to do the 300cc (286) stroker crank upgrade. Just swap the crank, balancer and piston, maybe an EJK. This is what I'm thinking of doing if my wife opts to get the CRF250L Rally this year.
    #50
  11. Cuttlefish

    Cuttlefish Riding to disappear.

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    I picked the crf300r/l up from Gerard last night.
    Took it for a quick spin around a couple of blocks before loading it into my van.
    I didn't find the gear ratios weird on that quick ride. Twist the throttle and now instead of having some more noise and little else there is mumbo!
    Gerard has ridden plenty of 250's and has worked for 4 years as a mechanic on Cape York adventure bike tours (with dr650s and drz400s) and as I said he now wants one.
    I've owned a Suzuki volty, Kawasaki super sherpa, Yamaha serow 225, Yamaha majesty 250, Vespa gt200 and a Vespa px200 over the years. I might add I've also owned all kinds of bikes from 100ccs to 1500ccs as well.
    All I can say is if you're happy with your crf250l but wish it had more power this is the answer.
    My low kms cbr300r engine cost $600 AUD. 38mm throttle body $95 and 300r ecu $120.
    You need to change one connecting plug on the leads that run from the stator to the harness.
    That is it it...the sum total of necessary modification required to install a cbr300r engine into a crf250l.
    One plug!
    Suddenly you have 8 hp and 45% more torque than the crf250l (cbr300r std specs).
    Start watching Ebay or calling wreckers for a cbr300r engine.
    Re-cap: I have an FMF Q4 with quiet insert and a mega bomb header. A K&N filter in a stock airbox.
    I'm just waiting to see what the day brings as its almost light but the weather radar is showing plenty of rain coming and the sky is full of constant lightning flashes and the the sound of thunder is rumbling through the hills.
    #51
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  12. swimmer

    swimmer armchair asshole

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    So the 300 ECU has no problem talking to the 250 combination meter?
    #52
  13. Cuttlefish

    Cuttlefish Riding to disappear.

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    Not so far...they both speak fluent Thai!
    :D
    #53
  14. swimmer

    swimmer armchair asshole

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    Why the need for the 300 ECU? So that it's running the correct fuel map for the 300 TB? I just wonder about thing like odometer error, fuel level error, etc. .

    I'm very close to buying a CRF250L Rally and given that has the same size TB as the 300 I wonder about using the Rally's ECU and TB with the 300.
    #54
  15. Cuttlefish

    Cuttlefish Riding to disappear.

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    I'll run that by Gerard and see what he says.
    I bought the coil as well just in case we needed it as I didn't want to have the engine turn up and then have to wait days for additional parts to be sent to get the bike to run.
    It's just going 5am here (Sunday) so I'll call him later and ask!
    #55
  16. Cuttlefish

    Cuttlefish Riding to disappear.

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    The big difference is the 45% increase in torque from the pre 17 crf250l to the cbr300r engine. Now I know what it feels like. the Cbr300r is also heavier than the crf250l.
    #56
  17. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    Because the 300 has a longer stroke and the timing is different from the 250 engine
    #57
  18. Traveller128

    Traveller128 Long timer

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    I said this back when the CBR300 hit the street. If they put that motor in the CRF, they'd sell a ton. Since it was emissions certified for the street in a U.S. spec bike already, I still don't understand why they haven't. Glad that worked out so well. Seems like a no-brainer power solution that Honda should just build. I still think Yamaha should make a WR300R, and Kawasaki should revamp their KLX and put the Ninja 300 motor in it. All those would make great dual sports.

    Congrats on getting yours up and running. Should make a really fun bike. Glad to hear that it worked out so well, and look forward to hearing more about it!
    #58
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  19. retroone

    retroone Long timer

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    pic
    #59
  20. Cuttlefish

    Cuttlefish Riding to disappear.

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    Pics on the way. Just got back from a fun 245 km shake down ride.
    Got to run a few errands and I'll post some pics and a ride report.
    #60