1981 RM125 race bike build

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3/8/2018 6:35 AM

Hi guys, thought I would share my most recent project on here...
I was given 2 blown up RMs by my Grandfather around 3 years ago, an '80 rm250 and an '81 rm125, which he purchased for a grand total of £1 back in 1983 when he was southern co-ordinator of the AMCA here in England. I finished the 250 around this time last year and had a great time racing it last summer. Photo

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However when winter time came I decided I needed another project to keep myself occupied, so started work on the 81 125 full floater... luckily my Dad and I had already bought a second 125 for cheap around the same time I finisbed the 250 last year.
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which helped as the one from my Granddad was probably too far gone:Photo
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So I got to work making 1 nice race bike built from the best parts out of the 2 bikes..
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honed and ported cylinder to go nicely with the original fresco exhaust system
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also decided to make a carbon chain guide:

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almost done

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Should get it all finished tomorrow night so will upload some more pics of the finished product!
Ill be racing the bike in the pre83 championships here in the UK which start in 3 weeks...

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3/8/2018 6:42 AM

Looks amazing! And cool story. I can't wait to see it finished.

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Throwbackmxguy

3/8/2018 6:42 AM

Very nice looking bikes! And the chain guide looks awesome as well. Very nice work

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3/9/2018 3:50 AM

I just bought a 1981 rm 125. Any advice on good places to source parts?

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3/9/2018 4:47 AM

Huckster wrote:

I just bought a 1981 rm 125. Any advice on good places to source parts?

in the UK I use Jk racing or Motoduro, harder to find NOS bits can be found on fowlers parts

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3/24/2018 11:06 AM

Sorry for the delay guys, only just got around to finishing it... enough talk, here is the finished product:


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3/24/2018 1:09 PM
Edited Date/Time: 3/24/2018 1:16 PM

Good work. You can tell someone cared when the details go down to nice carb vent lines.Sometimes I wish I built a 81 RM instead of a KX for vmxh. I loved my 81 RM125 back in the day
The chain guide came out really good. How did you make it?

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3/24/2018 2:03 PM

MaxPower wrote:

Good work. You can tell someone cared when the details go down to nice carb vent lines.Sometimes I wish I built a 81 RM instead of a KX for vmxh. I loved my 81 RM125 back in the day
The chain guide came out really good. How did you make it?

Thanks man, have really loved this build cant wait to go for a rip on it tomorrow!
Chain guide was a simple as buying some 3mm sheet and cutting out on the bandsaw and hole saw followng the shape of the original. then added a little polycarb sheet for some added protection before bolting in the NOS slider blocks. pretty simple job but really pleased with how it came out!

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3/25/2018 7:47 AM

Great work! Nice to see an old Zook given a good restoration. Enjoy your scoot, be safe!

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3/26/2018 3:05 AM

Sweet!

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3/27/2018 3:09 PM

Does anybody have an old mxa etc... shootout with dyno charts for the 81? If so please post it, thanks ☺

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3/28/2018 2:27 AM

kruspy378 wrote:

Does anybody have an old mxa etc... shootout with dyno charts for the 81? If so please post it, thanks ☺

I don't I'm afraid but after riding it on Sunday I would imagine it looks something like this:
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haha! tough work to keep it in the narrow power band but makes for a lot of fun!

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3/28/2018 3:10 AM

Hahaha, yeah i kind of set myself up for that one... Lightswitch kind of powerband for sure. Really has alot of top end pull.

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3/28/2018 7:02 AM
Edited Date/Time: 12/10/2018 8:43 AM

is the cylinder ported? I don't remember that bike having an unreasonable power deluvery

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3/28/2018 7:12 AM

I think it is, but not sure. Its not unreasonable but pretty pipey imho... Im also not a pro rider. Wish i was though. Pretty flat off the bottom, good midrange, but... past that, pulls like my 1990 cr125 did on top. Definately top end motor, at least mine is...

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3/28/2018 7:41 AM

MaxPower wrote:

is the cylinder ported? I don't remember that bike having an unreasonable power deluvery

Cylinder has some light porting work but only to improve flow, removing any sharp corners etc. Power delivery is not that unreasonable in reality but after riding a newish 125 with a power valve and then jumping on this really reminds you how to use the clutch and shift every 5 seconds

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3/28/2018 7:47 AM

MaxPower wrote:

is the cylinder ported? I don't remember that bike having an unreasonable power deluvery

36Wheeler wrote:

Cylinder has some light porting work but only to improve flow, removing any sharp corners etc. Power delivery is not that unreasonable in reality but after riding a newish 125 with a power valve and then jumping on this really reminds you how to use the clutch and shift every 5 seconds

Every 5 seconds sounds about correct... cheers ☺

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12/9/2018 6:53 AM

Did you use the MotoDuro CDI in your build? (bike looks fantastic BTW)

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