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Yamaha Cygnus NXC125 scooter

Discussion in 'Yamaha 250cc Singles' started by Mike Green, May 11, 2020.

  1. Mike Green

    Mike Green Well-Known Member Premium Member

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    My scooter is 229cc. Is that close enough to 250cc to go in here?
     
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  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Yeah why not, we're not absolute sitcklers for detail here, many many in the projects section aren't 250's - we adore a good project and your cleaved in two FZR250 will garner a lot of interest also
     
  3. Mike Green

    Mike Green Well-Known Member Premium Member

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    OK. I bought this scooter for doing commuting. I had to cross Auckland for the job I had at the time. I went with the 4 stroke so I wouldn't get tempted to port it and put a pipe on it. Can't get parts, too difficult, etc. 20,000Km later and the engine is more or less toast, probably due to doing full throttle runs from one end of the NW motorway a few too many times. Looking around I discovered RCScooters. It was downhill from there.
    Initially I went with Taida parts - crank, cylinder, and later head & cam. Initially about 165cc and later out to 202cc. That was good enough to warrant getting taller gearing
    Later I went with RCScooter stuff, a kit they do, with a big crank, tall block, big head valves but I used the T6 Taida cam from the previous build. Also got a Mikuni 33mm pumper carb from MikuniOZ. By now the ignition wasn't what the engine needed so it now has a programmable Ignitech ignition I had lying around.
    That was OK right up until my son destroyed it, completely. Now it's at 229cc with a similar crank but 6mm longer rod, better head which I've taken to with the grinder and a tall block which still needs a 6mm spacer under it. This time I went with a monster cam from RCScooters and roller rockers. The last rebuild I also went with a watercooled cylinder. I got an electric pump to circulate the water from Davies Craig.
    All the transmission has been upgraded as well and I had to put a high torque starter in as the motor wouldn't turn over. I had to upgrade the starter wiring as well.
    It's geared for about 170kmh measured on the dyno but I've probably only had it up to about 140kmh. It was still accelerating but I doubt it had much more left. Funnily, it will wheelstand away from the lights if you get a bit keen with the throttle even with the tall gearing.

    Scooter cylinder & pistonsmall.jpg Scooter clutchsmall.jpg Scooter crankshaft2small.jpg scooter2small.jpg
     
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  4. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    That's great. Shows what can be done with a bit of thought and the right bits.
     
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  5. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    You forgot to mention Money. I'm guessing all that wonderful work and parts didn't come too cheap!
     
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  6. Mike Green

    Mike Green Well-Known Member Premium Member

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    The bills have added up for sure. My son paid for the last lot. It set him back about NZ$2k for crank, cylinder and piston, head & cam. It's all from Taiwan and really good quality. The castings are beautiful. I forgot that it has an oil cooler as well and little billet heatsinks tappet covers and cam sprocket cover.
    I have a friend who lets me use his lathe and mill so do all my own machining. The only part of this engine and transmission that hasn't been replaced or machined is the transmission cover, and even there all the kickstart stuff has been removed. You could stand on the kickstart lever and it didn't even look like turning over.

    3.jpg 1.jpg SAM_2916 (640x480).jpg SAM_2917 (640x480).jpg SAM_2918 (640x480).jpg SAM_2924 (640x480).jpg
     
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  7. Mastroragno

    Mastroragno Active Member

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    Great job!!!!!
    I can't wait to see a picture of your scooter...
    That scooter took a place in my heart... It was my first scooter...bought new in 2006 (i was 29 but only rode bikes or vespas so far...)...my wife threw it against an Audi A2...

    During a holiday in Greece with my wife:
    Cygnus 06 046.jpg
     
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  8. Mike Green

    Mike Green Well-Known Member Premium Member

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    That is awesome. Poor scooter.

    I've made every effort to keep the scooter as low key as possible. Apart from a cheapy muffler the little radiator out front is the only giveaway. Hopefully I will be able to hide it away. I only put it out the front for starters to be sure of good cooling. Chris from RC Scooters reckons they run motors with the water cooled cylinder and air cooled head without the fan or shroud. That may be OK on a Zuma but the Cygnus motor is shrouded by the lower bodywork so I've left the fan and shroud in place. RG50 radiator.jpg
     
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  9. Mike Green

    Mike Green Well-Known Member Premium Member

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    To give an idea of the cam now in the bike. The smaller one in the image below is the Taida T6 cam. This cam is reasonably hot and works for larger motors around 200cc. The other one, on the right, is the new one. It has nearly 50% more lift at 7.3mm and more duration. I had to use the beefy roller rockers in the picture. The smaller rockers are Taida high performance rockers for use with their cams IMG_1338small.jpg IMG_1337small.jpg
     
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  10. Mike Green

    Mike Green Well-Known Member Premium Member

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    Awesome day here in Auckland today and it's been a while. Took it out for a play. Went about twice as far as planned on a good mix of motorway and country roads. This is not your old economical commuter scooter now. It chews through the petrol. I have run a lambda meter on it a while back and it isn't particularly rich. I'm thinking of putting the lambda meter back on for a bit. The scooter doesn't have the rush at full throttle like I think it should, especially considering how it goes at 1/2-3/4 throttle. It's still happy at an indicated 110Kmh+ on the motorway. Plenty of fun on the on ramps with cars that have to be in front of the scooter so they don't get held up.
     
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  11. Mike Green

    Mike Green Well-Known Member Premium Member

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    I put the Lambda meter on and sure enough it was tending lean at full throttle. I went up 2 mainjet sizes and it is a lot happier at full throttle. It may still like even a bit bigger jet. Either way it gets going even better at full throttle now. It's real easy cruising with the speedo needle buried in the bottom of the speedo. One little problem i have had on & off is a slightly erratic response to giving it a handful of throttle from the lights. It was also missing just a bit now and then when just cruising along. When I went to check the plug, it's something easy to check so why not, I found the plug cap had come off the plug. It hadn't come right off the plug but was just sitting over it, about 20mm up from where it should be. The surprising thing is that it ran at all. I knew the ignition was good, an Ignitech programmable DC CDI, but I didn't think it was that good. It might be time for a better plug cap and maybe a longer lead. The coil is on the frame and of course the whole motor moves with the suspension.
     
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  12. minimac

    minimac Active Member Premium Member Contributing Member

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    Late to the party here, but love what you're doing!
     
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Great work on this scooter. So what is the top speed of this beastie?
     
  14. Mike Green

    Mike Green Well-Known Member Premium Member

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    If I have the rev limit set to 10,500rpm it tops out at 170kmh on the dyno. It does have what they call "up gears" in the final drive. I doubt it will actually get to 170 though. It isn't hard to have the speedo needle jammed in the bottom of the speedo and at least a bit more speed added. The last number is 110, bottom of the speedo is at least 10kmh beyond that, and I've gone faster than that. I'm guessing about 140-150kmh on the road.
    What I have done lately is fit the original plug cap and lead. D
    oing this has completely cleared up how the engine runs. There is no hesitation or missing. I also went up one more jet size on the mainjet. It might be just a tiny bit rich at full throttle now at slightly lower revs. If I roll it on and get the revs up a bit, at less than 3/4 throttle, and then give it full throttle it's happy as.
     
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  15. Mike Green

    Mike Green Well-Known Member Premium Member

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    Over a year since last post and there's been heaps done. I wanted to get it all legal with a W.O.F. and registered etc. The W.O.F. guy was asking all sorts of questions and wasn't happy about the radiator out the front. Something about it not being pedestrian friendly. I ended up having to get it certified by a Low Volume vehicle guy after which the WOF guy was happyish. Part of that was moving the radiator which I now have under the seat. There is an electric fan which draws air through the radiator which is then ducted out the back. The good thing is that there is hardly anything visible to give away that it's modified. Scooter radiator2.JPG Scooter radiator1.JPG
     
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  16. Mastroragno

    Mastroragno Active Member

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    It's impossible to get legal such a modified bike in Italy... Anyway, great job! :thumb_ups:
     
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