My NSR’s oil pump just finally crapped out, and you can’t buy new ones anymore. No big deal, but I was a little unsure about how much oil to add in my gas tank. It takes a little over 5 liters to fill up an NSR tank. So for every 1000cc of gas do I put about 20-25cc of 2-stroke oil in? On the back of my Motul 510 2-stoke oil is says: 50:1 (2%) add 100ml to every 5 liters of gas, 33:1 (3%) add 150ml to every 5 liters of gas, and 25:1 add 200ml for every 5 liters of gas. The question then is which is better for me. I usually drive my NSR pretty hard, keeping the high RPM’s up. Just not sure which variation I should use. Thanks.
You need to add 2-3% depending on your engine condition and how hot you run it. In the summer I added a bit more but now that its winter you should be fine with 2%. This means about 200cc not 20cc every time you fill up. 2% of 10 liters gas is 200cc oil. Don’t ever forget or your engine will be blown… I also used higher quality, more expensive oil for performance as well as cleanliness.
If you just put oil in your gas you will run lean. The jets in the carb are sized to flow a given amount of fuel. When you mix oil into the fuel your jets will flow the same amount of fluid, but there will be less gas in that fluid. Even though the remainder is oil, there will not be enough gas to properly burn the oxygen the motor breathes and you’ll run lean.
On an NSR you want to run the oil mix at about 25:1 to 30:1. You will have to go up on the main jet from 135 to about 138 on the older models and 130 to 135 on the newer ones. You’ll probably get away with richening up the mixture on the idle mixture screw and lifting the needle one groove, and not have to change the idle jets.
[quote=“redwagon”]If you just put oil in your gas you will run lean. The jets in the carb are sized to flow a given amount of fuel. When you mix oil into the fuel your jets will flow the same amount of fluid, but there will be less gas in that fluid. Even though the remainder is oil, there will not be enough gas to properly burn the oxygen the motor breathes and you’ll run lean.
On an NSR you want to run the oil mix at about 25:1 to 30:1. You will have to go up on the main jet from 135 to about 138 on the older models and 130 to 135 on the newer ones. You’ll probably get away with richening up the mixture on the idle mixture screw and lifting the needle one groove, and not have to change the idle jets.[/quote]
Ok, Im running a bigger carb anyway, the stock NSR runs a 26mm carb, but Im running a 29mm. So should I still run a bigger main jet? Or do you think I already have one? I have also already liften the needle one groove.
Thanks temple. It seems whenever I fill up with gas, it only takes 5-6 liters. Maybe I am not looking at my receipt close enough. Yeah and I too always run more expensive oil for performance. Im a huge Motul fan, but that is me.
[quote=“rk1951”]
Ok, I’m running a bigger carb anyway, the stock NSR runs a 26mm carb, but I’m running a 29mm. So should I still run a bigger main jet? Or do you think I already have one? I have also already liften the needle one groove.[/quote]If you had your jetting correct before going prelube, you will have to increase your jet size. For sure you will run leaner than at present. Whether or not that is dangerously lean, as in to the point of detonation, is another matter. I always found with the Keihins the optimum jetting changes almost daily… almost like a real race bike. 
how is it you determine what the optimum settings are? Do you just have to go by feel?
I’m also surprised you lost your oil pump without destroying your engine. How did you find out just in time?
Um, you mean the premix ratio or the jetting? This guide will help you with jetting. For the premix ratio you should go with the recommendation on the can. If they give a range, go to the richer end of that range since small-bore, high-revving motors like the NSR need more oil than (say) outboard engines. Use a good quality synthetic oil. I always had very good results with Kymco’s own-brand, NSR-specific 2-stroke oil. It’s made in Japan and packaged for Kymco. One of the best kept secrets in the oil market IMO.
Thanks for the info. But I wonder if you really need so much on the premix. 25:1 would be like 4% right? I’ve noticed if i go up to 3% or more a definate decline in performance. Mabye if i tuned it correctly it would balance it out though. Also I’ve used alot of oil brands and I really didn’t notice a big difference between the common 2 stroke oil and the Japanese NSR specific brand. However, when using more expensive, high quality oil like Gulf or Repsol (around 500$ for a liter), there was a definate increase in responsiveness and power, and way less clouds of smoke left behind.
The NSR oil is very good and was formulated specially to reduce the amount of carbon that would collect on the RC valve. Other oils may show less smoke out the tailpipe but actually leave more in the engine. Using ‘race’ oil is not advised unless you plan to strip the engine down as often as a race bike’s. This is because real race lubricants leave a lot more gum behind that easily causes the rings to stick in their grooves or for the RC valve to jam up.
As to the amount used, you may have noticed that (with the pump in use) properly warmed up a regularly-thrashed NSR would hardly make visible smoke at all, except possibly when flat out. You could reduce the amount of oil you premix until you get similar results to the original condition. Just don’t go so far that there is no smoke at all at peak revs and WOT!
The reason you get a difference in performance between 3% and 4% is the effect on jetting, which I mentioned above. The jets can only pass so much fluid through them. When you increase the amount of oil passing through, the amount is automatically reduced. When you go to 4% oil, you are getting only 96% of the fuel you were with the pump running. You are running leaner than you were before. If you actually noticed a decrease in performance you are definitely running lean. 2-stroke performance is largely dependent on the effects of the expansion chamber. As exhaust gas temperature increases the effectiveness of the returning tuned waves to push unburnt mixture back into the cylinder increases with it. EGT increases as the mixture is tuned leaner. That means that power increases as you go leaner, right to the point where there is not enough fuel to properly burn all the oxygen in the cylinder, and detonation commences. Therefore, you pass straight from optimum power into an area where engine damage is occuring. The job of a race mechanic is to find that razor edge just before detonation. A street bike can afford a bit more margin of safety! If you need to run 4% oil then you need a bigger main jet. If you have a little visible smoke at 3% you should still try running one size larger on the main jet just to be sure it’s too large. You can easily tell if the main jet is too large by running up to about 6,000rpm and giving WOT and pulling up to peak revs. Then do it again at about 3/4 throttle. If the bike accelerates faster at 3/4 than at full throttle, your main jet is too large! My usual strategy is go up on the main jet until this phenomenon can be detected and then drop back to the last jet before that one. That’s close enough to the edge for a street bike.
Hope this helps.
[quote=“Temple”]how is it you determine what the optimum settings are? Do you just have to go by feel?
I’m also surprised you lost your oil pump without destroying your engine. How did you find out just in time?[/quote]
Well my oil pump started to have problems a while ago. Once about a year ago when I was on a big tour, more and more smoke started to pour out of the exhaust. I had myself and a good mechanic with me that said it was the oil pump. So we adjusted it, which made it a little better, but my performance was all coughed up with oil. So we disconnected half of it. I still had the oil lines running into the oil pump which still created vacuum, but it was disconnected from my throttle. So then I started adding oil in my tank as well. About 100mm, but I still had to add oil into my oil reservoir too, but not that often. The performance was great. I am still doing this, and there is still smoke at high RPM’s.
Actually my friends NSR last weekends started leaking horribly out of his oil pump. It was basically dripping none stop. So we took it into a couple of performance shops and they tried to find a new oil pump but no luck. So we disconnected it. And now we are adding oil to his tank.
Redwagen, thanks so seem like you really know what you are talking about. I really appreciate all the info man. Even though I have owned my NSR for 3 years, and rebuilt the engine twice (one time I fucked up), I am always scared about the oil situation. I don’t want to detonate my engine that way. Thanks.
No worries. 
No reason you should learn these things the hard way.
If you are running half premix and half injection you will probably be okay. The factory jetting is usually a little on the rich side to protect the owners from themselves, and the warranty department from getting overworked. I would keep looking for a functional oil pump as the system is generally very reliable and accurate, and it’s a pain having to calculate the dosage of oil to add each time you gas up. With race bikes it’s not so bad as you mix a fresh batch of gas for every day at the track and do it with presized containers. A smart NSR owner who plans to keep his bike for the long run will be stockpiling various parts and acquiring parts bikes when they come up. When I sold mine it went with enough parts to build almost two complete spare engines, and and and.
There are a couple of bearings in the engine which are special sizes and cannot be bought on the open market. When Kymco stop selling those (if they haven’t already) it’s only a matter of time before you have to come up with an expensive custom solution, go hunting for a good used one, or try to source from Thailand. Built in obsolescence is a bitch when no better product is available as a replacement!
[quote=“redwagon”]No worries. No reason you should learn these things the hard way.
When I sold mine it went with enough parts to build almost two complete spare engines, and and and.
There are a couple of bearings in the engine which are special sizes and cannot be bought on the open market. When Kymco stop selling those (if they haven’t already) it’s only a matter of time before you have to come up with an expensive custom solution, go hunting for a good used one, or try to source from Thailand. Built in obsolescence is a bitch when no better product is available as a replacement![/quote]
Yeah I have basically two engines, but only one good engine case. Also the last rebuild, I had to get some custom bearings because the Kymco ones were gone. Some of the performance shops around town that know me hate it when I pull up looking for a hard to find part. If you push them hard enough they will help you, but sometimes they say they can’t help me. There is even a junk yard close to my house and everyone once in awhile I check to see what kind of NSR parts are available out there. NSR’s are really dying here in Taiwan, but that is also why I like them so much. They are rare, and a great buy for the performace you get out of them. No other 150cc can touch them on the road in Taiwan.
[quote=“rk1951”]Also the last rebuild, I had to get some custom bearings because the Kymco ones were gone.[/quote]Exactly. I think you can still get them from Thailand however. Bit tricky unless you’re going there.[quote]They are rare, and a great buy for the performace you get out of them. No other 150cc can touch them on the road in Taiwan.[/quote]I loved mine to bits. I think you have to look at imported 4-strokes over 400cc to beat a good NSR in a straight line, and unless it’s quite steep uphill they are hard to catch with anything in the mountains.
It’s too bad they:
Stopped making them.
Didn’t give it the plated cylinder.
Ruined the later ones with the ugly bodywork.
Ditto the stupid RC valve computer.
Never taught Ah-Huang how to service it properly.
Stopped stocking all the parts.
Didn’t give the Taiwan version the alloy frame.
Ditto the bell-crank monoshock system.
Never brought the 250 to Taiwan.
Oh well. I had fun with mine the 10 years I had it. 
:happybiker:
[quote=“redwagon”]
It’s too bad they:
Stopped making them.
Didn’t give it the plated cylinder.
Ruined the later ones with the ugly bodywork.
Ditto the stupid RC valve computer.
Never taught Ah-Huang how to service it properly.
Stopped stocking all the parts.
Didn’t give the Taiwan version the alloy frame.
Ditto the bell-crank monoshock system.
Never brought the 250 to Taiwan.
Oh well. I had fun with mine the 10 years I had it. :happybiker:[/quote]
Hahah yeah I agree with all those. I really wish Taiwan had the 250, I would be all over that. I really don’t think many people at least where I live know how to service these dinosaurs anymore. Which is fine because when you do it your self ya know you do it right. But sometimes I just want it fixed and I don’t have the time. I have thought about buying a Honda 400cc, but why they are so much more expensive and I think the NSR is a little better on performance. Not nearly as realiable though. Do you have any picks of your NSR? Man, mine has been the best thing since I have owned it for the last 3 years, I love them!! I just drove her to Ilan last weekend from Chongli. She ran like a dream.
I guess its necessary to learn how to maintenence NSRs if you wanna keep them alive and in good shape. My old mechanic knew what he was doing, but he was always reluctant to help me fix all the little things or tune it up. In fact 3 days before my engine blew, i could feel/hear it coming and I asked him to take a look at it, but he kindof blew me off. Since then i havent gone back. You seem to really know what you’re talking about redwagon. How did you learn all the stuff about NSRs? There arent any guides in english are there? I had a hard time even finding any info on the web about NSRs.
And yea a terrible shame about the 250s 
They would be the perfect bike for me in Taiwan. I heard about 10 years ago they had their time, but we missed out…
Also rk, the road to yilan is awesome, and perfect for our bikes Me and my roommate used to do it all the time. Hopefully we can again soon!
I used to wrench on 2-stroke production racers back in the day. In Taiwan I built a bunch of hopped up RZ’s and HX’s. I got my first NSR in 1992 and kept it until about 2002. That was ported, ran a forged piston, higher compression, overbored carb at first and later a PWK, and an extrude-honed cylinder. I grafted the FZR rear monoshock and bell cranks on it and modified the fork springs and valving myself. Um, yeah, and a whole other list of mods too dull to mention. In the meantime I had a few other NSRs and also tuned some for friends. I use the basic tuning principles that all 2-strokes respond to, and design porting changes via software. I also did a lot of research into the NSR’s RC valve and ignition computers, spent a bunch of time talking to Kymco engineers etc. Then I looked into how the 250’s are tuned, what are the differences between the two, how the NSR and RS motors differ… and whole lot of other stuff which is totally boring to 99.99% of the population! 
Tuning for production racing is neat in that you are very limited in what components you can change for performance or bespoke items. It’s good preparation for tuning bikes that have little aftermarket support, or a market where very few useful parts are on the market.
Still looking for a photo of my NSR. Will post it when I find it.
wow… where do you live?? maybe you can help me tune up my new bike or give me some tips. Actually I don’t really know that much about maintenence. I used to take it in all the time, but the way my old mechanic liked to work was that once something breaks he’d fix it if it was necessary… I’ll be getting a first generation Japanese NSR pretty soon, so I have high hopes that it’ll put out some good performance. I’d like to keep it alive and running well if i can. I tend to kill my vehicles at pretty quick rate
[quote=“redwagon”]I used to wrench on 2-stroke production racers back in the day. In Taiwan I built a bunch of hopped up RZ’s and HX’s. I got my first NSR in 1992 and kept it until about 2002. That was ported, ran a forged piston, higher compression, overbored carb at first and later a PWK, and an extrude-honed cylinder. I grafted the FZR rear monoshock and bell cranks on it and modified the fork springs and valving myself. Um, yeah, and a whole other list of mods too dull to mention. In the meantime I had a few other NSRs and also tuned some for friends. I use the basic tuning principles that all 2-strokes respond to, and design porting changes via software. I also did a lot of research into the NSR’s RC valve and ignition computers, spent a bunch of time talking to Kymco engineers etc. Then I looked into how the 250’s are tuned, what are the differences between the two, how the NSR and RS motors differ… and whole lot of other stuff which is totally boring to 99.99% of the population! Tuning for production racing is neat in that you are very limited in what components you can change for performance or bespoke items. It’s good preparation for tuning bikes that have little aftermarket support, or a market where very few useful parts are on the market.
Still looking for a photo of my NSR. Will post it when I find it.[/quote]
Yeah thanks Redwagen, your the first person I have met besides a good Taiwanese friend of mine that really knows what you are talking about with NSR’s. I have done all the work on my NSR, but I have only been around two strokes for the past 3 years. So I am still a newbie. So yeah where are you located anyway? I will take some nice pics of my NSR in the next week and post them. But keep looking for yours. Thanks so much for all your imput.
Yeah Temple, I have ridden most roads out to Ilan before, but yeah once you get you bike running again let me know. ABout a year ago I drove my NSR around the entire island. I went from Chongli to Kenting in one day (10 hours), but I was with some slower motorcycles so maybe I could do it faster. Anyway I would love to do it again. Also man, if you need help with your new bike to get it running don’t hesitate to call me. I have all the tools, and I have probably fixed that problem before too. I live pretty close to ya.
Sorry guys. Much as I’d like to help you, I’m no longer resident on the septic isle. Happy to answer your questions online, where I can help. Unfortunately I passed on all my shop notes with the bike, but what I remember I’m happy to share with you.