NS125F Top speed?

[brown_d9]

My 1988 NS125F has been fully dereistricted with an aftermarket exhaust system courtesy of micron, with a 120 main jet and standarg gearing etc etc.

But in top gear it maxes out at 9000rpm which i expected as it would be a miracle for it to reline in top, being a rotten 2squeek, but at this engine speed it is doing an indicated 80mph which i thought would be more like 90-100, would going up another 1 or 2 main jet sizes give me that little bit more power at the top end?

Thanks in advance for all the help.

[Kickstart]

Hi

They would indicate around 80 anyway when restricted (the speedo was one of the less accurate ones when they were new). Unlike most sports 2 strokes they will not rev out well, mainly due to the way Honda restricted them by leaving the ATAC chamber open in the low revs position.

I would expect an indicated 95mph+ from an NS, with a real 85~90 top speed if properly derestricted.

All the best

Keith
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[brown_d9]

Would a bigger mainjet make it a bit quicker though, there is nothing bad that can happen from having too bigger main jet is there, so i thought a bigger one might help?

[Hex]

It would allow to much fuel in and basically flood the engine, thus making it run slower/bog down.

Bigger is not always better, ideally you want the correct one for the engines needs.
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[Kickstart]

Hi

As above. Bigger is safer (you are unlikely to suffer sudden terminal engine failure from using a main jet a bit too big, quite probably from using one slightly too small), but not better.

You need the right size for best results. Just like increasing the mains up to 300V would not give you a better TV picture.

The NS airbox was meant to be quite restrictive. Drilling holes in it (make sure you drill them in the right place) or replacing it with a K&N were both quite good for performance, just make sure you rejet to get it right.

Also, check your sprockets. Sound to me as though someone has lowered the gearing.

All the best

Keith
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[clemsta]

I have a NS125R, with a Allspeed pipe and a K&N type filter, the filter makes it sound really throaty and a lot louder. I've also put a 120 main jet in and i've put the clip on the needle second from bottom, but it sounds rough and between 3/4 and full throttle you can feel it holding back, if you pull full throttle it does not accelerate any harder than if it were at 3/4 throttle but it makes more noise. I haven't touched the mixture screw after adding the pipe and filter, do you screw out to richen and in to lean?


Is there such a thing as a 2 stroke exhaust gas analyser, if there was then you could tell when it was running rich and lean at different rpms.

Has anybody got any suggestions on what to do next.

Thanks in advance
Adam
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[brown_d9]

You need to do a plug chop, ask around on here as im not 100% sure how to do them.

[Kickstart]

[andi_woodley]

Where do you get new carb jets from???
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Andi Woodley

[Kickstart]

[plugger147]

I'm pretty sure the standard one was a 110, I had a 120 in mine with a micron and drilled airbox and it'd read at a tad over 90. I did try it with a K&N but couldn't get it to run smoothly enough no matter how much I tried it'd have a flat spot somewhere, ditched it and went back to the airbox and set it up to run fine.
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[alains]

the needle position is surely too low , try to set the clip higher
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