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Looking for help, and advise on 1991NSR250 motor


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Alan Smith

 
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Joined: 26 Nov 2018
Location: Tacoma WA USA
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Looking for help, and advise on 1991NSR250 motor

Wed Sep 25, 2024 7:51 pm » Post: #1 » Download Post

looking for help with an nsr 250 engine the builder was Harry Okuda

I want to fit this in a 1989 NSR250 Terra Racing chassis. Any help or advise greatly appreciated.
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scottvor

 
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Location: Carlsbad, CA USA
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Sun Sep 29, 2024 1:44 pm » Post: #2 » Download Post

Alan,

If you got your motor from Iconic, that is one trick bit of kit right there. I have only owned MC21/28 but AFAIK the MC21/28 cases should fit in MC18. I know the pickup wiring harness is different from MC21/28 to MC18. Doesn't mean it wouldn't work. Slight timing difference between MC21 and 28 flywheels, unsure if MC18 is different as well. You'll have to check oil pump connectors between your MC18 and MC21.

You should compare MC21 to MC18 wiring diagram to figure this out.

You should also do a leak down test on the motor (if its from Iconic).

I have a comparable motor in my MC28. I'm happy to give you my jetting setup. Well.... my motor might be a bit tricker than that Okuda built motor.

Scott
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MC28SP, '16 KTM 500EXC, '16 Beta Xtrainer, '07 BMW 1200GS, '96 Ducati 900SS
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Andy
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1991 Honda NSR250 MC21
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Wed Oct 02, 2024 12:25 am » Post: #3 » Download Post

Hello Alan, and welcome to NSR-WORLD!

Technically, the '88-'96 motors are all interchangeable, only the 1987 won't easily transfer, as it has solid engine mounts as opposed to the later models' rubber mounts. There are however a number of differences to sort through, such as GPS (Gear Position Sensor)/neutral switches, A/C generator harnesses, ignitor coil harnesses/flywheels etc. Just make sure not to mix-and-match model parts, no matter how similar they may look, as it can lead to issues. (I.e. use all 1989 MC18 [R5/6K] OR '90-'93 MC21 components, including the carbs, air correction, and PGM.)
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