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Honda NSR 125 stuttering after switching from pump to mix

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Simon13245
Borekit Bruiser



Joined: 19 Jun 2021
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PostPosted: 10:04 - 13 Jul 2022    Post subject: Honda NSR 125 stuttering after switching from pump to mix Reply with quote
Hello there guys Smile

It's been a while since I last posted. During that time my NSR broke two times Razz After the first breakdown, I changed the wossner piston, to a new OEM nicasil cylinder. The second breakdown required a new crank and everything that goes with it. Huge thanks to Alain for all the guidance.

After the second breakdown, my mechanic told me to ditch the oil pump and just go with the mixing of gas/oil. I'm using Ipone Samourai 2T Racing 50:1. After the repair and after ditching the oil injection, it struggles to go past 6-7k rpm on full throttle. It stutters, it shakes, and after a couple of seconds, it finally manages to go past 6-7k rpm, and then it pulls until the red line with no problems.

No carb settings were changed, everything is the same. Before the repair there was no problem, it was quick and had no problem going from 4-5k rpm to the red line with full throttle.

What do you guys think? Does it sound to you like too much fuel? I've read a lot of posts about premix, and I'm confused. What would you do? Maybe dropping the needle one notch down to limit the fuel?
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Honda NSR 125R (1999)
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Easy-X
Super Spammer



Joined: 08 Mar 2019
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PostPosted: 10:08 - 13 Jul 2022    Post subject: Reply with quote
Possibly the reverse: too little fuel - you've replaced a small volume of the petrol with oil. It does sound like the needle position would help. I'd try moving the clip down (needle up.)
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter
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Zen Dog
World Chat Champion



Joined: 11 Aug 2004
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PostPosted: 10:12 - 13 Jul 2022    Post subject: Reply with quote
This sounds EXACTLY like a problem I had on my NSR years ago. Took me an age to figure out.

The actuator for the powervalve had been put back on the wrong way around, so it was closing when it should have been opening. Think I just flipped the pulley thing the other way round (we're accessing the deep recesses of my memory now) and it was instantly fixed.
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Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011
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A100man
World Chat Champion



Joined: 19 Aug 2013
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PostPosted: 10:21 - 13 Jul 2022    Post subject: Reply with quote
Who's Alain?
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Zen Dog
World Chat Champion



Joined: 11 Aug 2004
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PostPosted: 10:30 - 13 Jul 2022    Post subject: Reply with quote
A100man wrote:
Who's Alain?


This guy - https://www.bikechatforums.com/profile.php?mode=viewprofile&u=3362.

Our resident French NSR guru. Posts very rarely, I didn't know he was still around to be honest, but if you've got an NSR125, he's the man to speak to.
____________________
Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 11:26 - 13 Jul 2022    Post subject: Reply with quote
Get a new mechanic as he doesn't have a clue what he's talking about. I've had countless Japanese two strokes over the years, and I've spoken to countless people who've had Japanese two strokes and I've NEVER heard of an autolube pump failing in that time.

Honestly, run away, find a mechanic who is actually good.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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A100man
World Chat Champion



Joined: 19 Aug 2013
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PostPosted: 11:34 - 13 Jul 2022    Post subject: Reply with quote
Zen Dog wrote:
A100man wrote:
Who's Alain?


This guy - https://www.bikechatforums.com/profile.php?mode=viewprofile&u=3362.

Our resident French NSR guru. Posts very rarely, I didn't know he was still around to be honest, but if you've got an NSR125, he's the man to speak to.


Cool
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Simon13245
Borekit Bruiser



Joined: 19 Jun 2021
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PostPosted: 12:24 - 13 Jul 2022    Post subject: Reply with quote
Easy-X wrote:
Possibly the reverse: too little fuel - you've replaced a small volume of the petrol with oil. It does sound like the needle position would help. I'd try moving the clip down (needle up.)


I think you are right, it makes more sense than just giving it less fuel. I will try that out, thank you.

Zen Dog wrote:
This sounds EXACTLY like a problem I had on my NSR years ago. Took me an age to figure out.

The actuator for the powervalve had been put back on the wrong way around, so it was closing when it should have been opening. Think I just flipped the pulley thing the other way round (we're accessing the deep recesses of my memory now) and it was instantly fixed.


That may be possible. Maybe the mechanic mounted those cables the other way around. I will check it out as well. Thank you.

MarJay wrote:
Get a new mechanic as he doesn't have a clue what he's talking about. I've had countless Japanese two strokes over the years, and I've spoken to countless people who've had Japanese two strokes and I've NEVER heard of an autolube pump failing in that time.

Honestly, run away, find a mechanic who is actually good.


He said that because the rod was in a shape of an egg. I did everything right (I think) in terms of the oil pump. I repaired the rubber part that was leaking, I bled the air out of it, I set it just like the manual says, and yet the rod somehow got extremely hot and deformed.
My mechanic is also racing on two strokes, typical dirt bikes and that's why he recommended to me to just switch to premix. I was just as surprised as you because I have NEVER heard a bad story about NSR pump, and also the piston and cylinder were in perfect shape.
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blurredman
World Chat Champion



Joined: 18 Sep 2010
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PostPosted: 12:41 - 13 Jul 2022    Post subject: Reply with quote
You'll get a lot of contention in regards to premix vs pump.

Just go with what you like. Pump is convenient and also variably economic in oil consumption.

But pre-mix is a lighter throttle, and it is fine. Put a blanking plate for the pump mount. Carry the bottle, do the maths at the pump.

You can change carburettor settings if required, but i've never done so. 1-2% less fuel is not going to blow engines up. However- if we have a resident NSR expert I would fully use him Cool
____________________
CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S.
Current: 1973 MZ ES250/2 - 17k. , 1979 Suzuki TS185ER - 9k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 38k, 1989 MZ ETZ251 - 49k
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 14:02 - 13 Jul 2022    Post subject: Reply with quote
Simon13245 wrote:

My mechanic is also racing on two strokes, typical dirt bikes and that's why he recommended to me to just switch to premix. I was just as surprised as you because I have NEVER heard a bad story about NSR pump, and also the piston and cylinder were in perfect shape.


Yet, he doesn't know you need to change the jetting when you change to premix? The mixture of fuel and oil actually makes the engine run lean because the mixture is a mixture rather than pure pterol
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Zen Dog
World Chat Champion



Joined: 11 Aug 2004
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PostPosted: 14:37 - 13 Jul 2022    Post subject: Reply with quote
Simon13245 wrote:
Zen Dog wrote:
This sounds EXACTLY like a problem I had on my NSR years ago. Took me an age to figure out.

The actuator for the powervalve had been put back on the wrong way around, so it was closing when it should have been opening. Think I just flipped the pulley thing the other way round (we're accessing the deep recesses of my memory now) and it was instantly fixed.


That may be possible. Maybe the mechanic mounted those cables the other way around. I will check it out as well. Thank you.


There is nothing preventing it just being put on the wrong way around if I remember right, so it's easily done.
____________________
Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011
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redeem ouzzer
World Chat Champion



Joined: 06 Oct 2015
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PostPosted: 14:59 - 13 Jul 2022    Post subject: Reply with quote
Junking the oil pump is a good move, less weight, better throttle response and you know the engine is wet at maximum welly.

But yep you'll be needing to go up on the pilot and main jets by a size or two.
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Simon13245
Borekit Bruiser



Joined: 19 Jun 2021
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PostPosted: 16:02 - 13 Jul 2022    Post subject: Reply with quote
MarJay wrote:
Simon13245 wrote:

My mechanic is also racing on two strokes, typical dirt bikes and that's why he recommended to me to just switch to premix. I was just as surprised as you because I have NEVER heard a bad story about NSR pump, and also the piston and cylinder were in perfect shape.


Yet, he doesn't know you need to change the jetting when you change to premix? The mixture of fuel and oil actually makes the engine run lean because the mixture is a mixture rather than pure pterol


I don't know man, he probably does know. I'm really struggling to find a solid mechanic around here. He is my 3rd try. He did the piston + cylinder for me, and now he did the rod. Overall I'm quite happy with him.

Zen Dog wrote:


There is nothing preventing it just being put on the wrong way around if I remember right, so it's easily done.


I did some testing, and it seems that the cables are the right way.

Also, I changed the position of the needle to give the bike more fuel, it did make a difference. It still struggles a bit but it's much better now.

redeem ouzzer wrote:
Junking the oil pump is a good move, less weight, better throttle response and you know the engine is wet at maximum welly.

But yep you'll be needing to go up on the pilot and main jets by a size or two.


Yeah, that is probably the ultimate solution. I will have to upjet a bit because the needle position helped but it's not perfect.

Thank you for all the suggestions, you helped me to get on the right track.
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Honda NSR 125R (1999)
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B1N
Scooby Slapper



Joined: 13 Feb 2022
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PostPosted: 22:01 - 13 Jul 2022    Post subject: Reply with quote
I'm not familiar with the NSR oil system but if you delete any oil pump you need to make sure all 2 stroke oil ways from the pump to the engine are plugged and air tight.
If not the engine will draw air in where there used to be oil leading to lean fuel/air mix.
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P.
Red Rocket



Joined: 14 Feb 2008
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PostPosted: 08:38 - 14 Jul 2022    Post subject: Reply with quote
Changing the needle won't let more fuel squirt through the hole... Changing the jetting however is a must.
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Simon13245
Borekit Bruiser



Joined: 19 Jun 2021
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PostPosted: 12:03 - 14 Jul 2022    Post subject: Reply with quote
B1N wrote:
I'm not familiar with the NSR oil system but if you delete any oil pump you need to make sure all 2 stroke oil ways from the pump to the engine are plugged and air tight.
If not the engine will draw air in where there used to be oil leading to lean fuel/air mix.


Thank you for the tip. The hose that goes to the carb is sealed so that there is no extra air getting into the engine.

Paddy. wrote:
Changing the needle won't let more fuel squirt through the hole... Changing the jetting however is a must.


I agree. Right now the jets are:
- 138 main,
- 65 choke,
- 42 idle,
- 65 power jet.

I am planning to change to main, idle and power jets to a bigger ones.

I also noticed that there is quite a lot of black sludge coming out of the exhaust. It's quite interesting actually. Needle up (more fuel) helped a lot, but now it's producing tons of black spooge from the exhaust...
Seriously I like this motorbike but I think it's time for a modern injected 4-stroke.
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