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Thread: Yamaha NXC125 20,000km

  1. #91
    Join Date
    10th May 2006 - 10:37
    Bike
    Aprilia RSV Mille & Yamaha FZR 400
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    Torbay, North Shore, Akld
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    512
    Quote Originally Posted by speedpro View Post
    Went for a ride in the weekend with my son on his Yamaha Scorpio. He followed the whole way up through Swanson to Taupaki and then Blossoms Cafe. The Scorpio is good for 18hp(claimed) and he was saying the scooter walked away from him in places despite him being in the right gear and giving it a handful. He's done a bit of racing so knows what you need to do to get along. He doesn't weigh much either so all the better. Away from lights on the way to Swanson he reckons no way he was staying with the scooter. No surprises really.
    Starting is way better with the new clutch and gear and it still goes off the clock plus a decent bit more so it's still fun to ride.
    Glad to hear its going well
    How about a pic ?
    RSV Mille: No madam, its an Aprilia, not a Harley. If it were a Harley, I would be pushing it !

  2. #92
    Join Date
    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    Page 5 has a lot of the new motor bits on it. Otherwise the scooter looks pretty normal except the exhaust and the oil cooler

  3. #93
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    Scooter is going good and it was a nice day yesterday. Out for lunch with my son. Quick video of throttle and speedo, private test track etc etc

    https://www.youtube.com/watch?v=2yVU_WdTlaU&t=2s

  4. #94
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Small problem with muffler let all the packing out so had to fix it and repack. Noticeably different tone and a bit quieter with the fresh packing. I put the little end piece in as well to quieten it even more. My son has taken it into town and back and was saying he thought with the cooler weather that it may have been going better than before which is what I have been thinking as well. Speedo able to be pegged down past the oil change light no problem evidently. May be time to put the Lambda meter back on and check the full throttle readings. Probably should sort out a smaller pilot jet as well.

  5. #95
    Join Date
    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    Got a bit of time so had the carb off. It already has the smallest main jet I have in the range. I do have smaller but they are 4-5 steps smaller and I prefer to sneak up on things. I did put in a smaller pilot jet and unwound the idle mixture screw 1/2 turn. Still starts easy but noticeably the idle is a bit lower and rougher. I need to make a very short screwdriver to get to the screw as it is on the bottom of the carb throat where it enters the engine. On the scooter it is a close fit with the cases, see the attached photo. Being on the engine side of the carb the screw is a fuel screw, winding it out adds fuel. On the air filter side it would be an air screw.
    I took it for a ride to be sure it was still good and didn't have a stumble off idle. No obvious problem with fueling but did have a couple of little problems at lights. I snuck to the front at one set and gave it a handful on the green. There must have been a slightly damp patch as the rear spun and launched sideways, just like it has on the dyno. At the next set of lights I didn't give it such a sudden handful and was most of the way across the intersection before I got the front back on the ground.
    Must say I prefer it now that it is a lot quieter. Even giving it throttle the noise is reasonable and I haven't noticed any real drop in performance. Power wise it is still happy on the motorway with the speedo pegged with plenty of throttle to go.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #96
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    It's good having a bit of time off and being able to play with things at leisure. I've made a 10mm long screwdriver from a 6mm bolt by filing the end of the bolt into a screwdriver shape. Works great. I also fitted the lambda sensor to see what fuel ratio it liked and also to confirm what I said about the screw adjustment. The screw adjustment is quite sensitive. Even with the smaller pilot jet it was still a bit less than 1 turn from bottomed at the ideal position. I went down to the next jet and adjusted the screw to 1.5 turns from bottom. Once back together it fired up after a few cranks getting fuel back in the carb and settled down nicely. It was sounding rich and the Lambda meter confirmed it so I screwed it in until the meter said it was in it's happy place. Less than 1/2 turn had it indicating about 14:1 and the idle getting a bit uneven. At idle it seems to like about 10:1 which is attained with this jet when the fuel screw out just over 1 turn from bottomed. Not road tested but it responds to throttle OK and the Lambda isn't jumping about too much apart from when the throttle is snapped closed and it goes lean until the revs drop.

  7. #97
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    Damn.

    Scooter came home on the trailer today. Son took it to Uni, lectured cancelled, came straight home. Possibly going a bit faster than usual down the NW motorway. Made funny squeeking noises as he went up the Te Atatu turnoff and stopped at the top. No compression when tried starting it.

  8. #98
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    It's toast.

    There was a small oil leak from the crank seal behind the variator into the transmission cavity and out the back. Oil level was real low, and it got real hot, then it stopped. It's completely wrecked inside.

    So, does it get rebuilt, binned, or something else?

    Parts are being costed as I type.

  9. #99
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    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Decision made. Same bore and stroke but with a slightly bigger cylinder head running the same cam. Cylinder is watercooled, head is left on it's own for cooling. The fan will be removed along with all the shrouds. Supposedly it's all good like that. Just got to sort out a radiator and pump and fan and controller. Looks like it is going to have to be under the seat in the storage compartment but we'll see once it is together. More power

  10. #100
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    12th February 2004 - 10:29
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    Box of interesting bits has arrived at work. Almost pulled a "sicky"

  11. #101
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    5th January 2007 - 14:58
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    motocompo
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    Buttfuck nowhere
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    Here's an easy to source 12v water pump that could be useful in this application.
    Every '90's 5 & 7 series BMW had one.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  12. #102
    Join Date
    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Henderson, Waitakere
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    Pump all sorted thanks. I went with a Davies Craig EBP15. Brushless Bosch motor and magnetically coupled. 1.4A current draw depending on load so should be manageable.

  13. #103
    Join Date
    12th February 2004 - 10:29
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    bucket FZR/MB100
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    Interesting the bits that have arrived. The watercooled cylinder has had a jacket welded on over the fins which I wasn't expecting. I've been there so it really doesn't worry me.
    The crankshaft is the same as the old one but has an even longer rod. The old rod was 97mm long and the new one is 103mm long. The cylinder is very slightly shorter than the old one but there is a spacer plate and 2 gaskets to go under it making the whole thing even taller. 6mm taller probably. There is less stud poking out the top for sure. The problem is that even though I had a longer cam chain for the last motor the extra height requires an even longer camchain which I will need to get. Unless it is packed in with the long stud set that came with the motor which we haven't opened yet.
    The cylinder head is apparently a blank canvas with metal left in to be removed by the tuner. I'm going to have to dismantle it to remove metal from the valve pockets and to blend the valve seats into the ports. The intake valves are up .5mm at 24.5mm but the exhaust valves are down .5mm at 21.5mm as compared to the old Taida head. The exhaust port is a good 1.5mm smaller diameter at the gasket face. I've asked if that is the hot setup or if they have just shipped what they had on the shelf. The motor went real good with the Taida head and from experience I can't see smaller valves making it go better. As usual all the bits look real good. The little 66mm forged piston is real nice.

  14. #104
    Join Date
    12th February 2004 - 10:29
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    Okay, bits have been dummied up to get an idea of clearances. The flat perimeter of the piston to the matching flat area of the head is 1.2-1.3mm clearance which seems fairly generous to me. This is with both base gaskets and the spacer plate and a used head gasket. The piston has reasonably sharp edges around the valve pockets so I'll be removing those edges and smoothing it out with wet&dry. The head needs lots of work. As you can see in the photos the valve seats are sunk into sharp edged pockets. I'm no expert on the desired combustion chamber shape but I'm going to be unmasking the valves and blending the pockets into the chamber. I'll leave as much of the flat head gasket surface that protrudes into the chamber as possible. This will aid turbulence and keep compression up. Retaining turbulence will speed combustion and reduce the need for ignition advance both of which are good.
    The intake port on the head has an angled cut centred on the manifold mounting studs. The outer diameter matches my adaptor I made. I'll be taking the port out to match the outer circumference.
    The exhaust port is small. There is a lot of aluminium that could be removed. Unless there is something crook with the exhaust ports which becomes obvious when I remove the valves I won't be taking much out of the port. It seems like giving the small port a try won't hurt. I am however mindful that a while back Chris of RC Scooters did mention that they use heads with 26mm & 23mm valves but I think that was on their race motors. This head has 24.5mm & 21.5mm valves which seems like it might be a better option for the street. I certainly had no complaints about the Taida head with 24mm & 22mm valves.
    I've thrown in a photo of the connections for the oil cooler.
    As much as Chris maintains that the head will be fine with no ducted cooling going to it I'm having problems with the idea. Chris says they have been running motors with watercooled cylinders and no fan or ducts for years with no problems. Maybe I'll clamp a CHT sensor on and monitor it with a Mychron date logger. I do have a fan controller with oil and water temp sensors so will be able to keep an eye on things. No logging unfortunately but may be able to run a sensor to the Mychron and log it that way.
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  15. #105
    Join Date
    20th January 2010 - 14:41
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    husaberg
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    The Wild Wild West
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    9,907
    Quote Originally Posted by speedpro View Post
    Okay, bits have been dummied up to get an idea of clearances. The flat perimeter of the piston to the matching flat area of the head is 1.2-1.3mm clearance which seems fairly generous to me. This is with both base gaskets and the spacer plate and a used head gasket. The piston has reasonably sharp edges around the valve pockets so I'll be removing those edges and smoothing it out with wet&dry. The head needs lots of work. As you can see in the photos the valve seats are sunk into sharp edged pockets. I'm no expert on the desired combustion chamber shape but I'm going to be unmasking the valves and blending the pockets into the chamber. I'll leave as much of the flat head gasket surface that protrudes into the chamber as possible. This will aid turbulence and keep compression up. Retaining turbulence will speed combustion and reduce the need for ignition advance both of which are good.
    The intake port on the head has an angled cut centred on the manifold mounting studs. The outer diameter matches my adaptor I made. I'll be taking the port out to match the outer circumference.
    The exhaust port is small. There is a lot of aluminium that could be removed. Unless there is something crook with the exhaust ports which becomes obvious when I remove the valves I won't be taking much out of the port. It seems like giving the small port a try won't hurt. I am however mindful that a while back Chris of RC Scooters did mention that they use heads with 26mm & 23mm valves but I think that was on their race motors. This head has 24.5mm & 21.5mm valves which seems like it might be a better option for the street. I certainly had no complaints about the Taida head with 24mm & 22mm valves.
    I've thrown in a photo of the connections for the oil cooler.
    As much as Chris maintains that the head will be fine with no ducted cooling going to it I'm having problems with the idea. Chris says they have been running motors with watercooled cylinders and no fan or ducts for years with no problems. Maybe I'll clamp a CHT sensor on and monitor it with a Mychron date logger. I do have a fan controller with oil and water temp sensors so will be able to keep an eye on things. No logging unfortunately but may be able to run a sensor to the Mychron and log it that way.
    Is there only two squish areas rather than 4 on that piston head combo?



    Kinky is using a feather. Perverted is using the whole chicken

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