NSR Carb Issue

[MikeKP61]

Id say this is one for Alains but up for anyone who might help. I have rebuilt a 99 NSR125R JC22. The top end was rebuilt, new TYGA exhaust, Boysen reeds and iridium plug. It idles and runs prefect and pulls through all the gears fine, also has the unrestricted Cdi.

The main issue is when putting the engine under load at low revs the engine bogs down. If i keep the revs high its fine (around 3500RPM) but I know it shouldn't be bogging down so much at 2000RPM.

I've negated this slightly by setting the mixture screw on the carb to almost 4 turns out but I think it can be resolved with the correct carb jet. Possibly a larger main or pilot jet or something? The current jets are Main 138 Idle 42 Power 65. Would any 2stroke heads be able to help?

Thank you!

[stirlinggaz]

Hi,
138/42/65 are the recommended jets for full power jc22.
I have 2 & both are pretty gutless below 3500rpm, I'm sorry that doesn't help much, but 2t's like the nsr arn't designed to be rode around at such low revs, ride it like you stole it & forget about riding it below 4000rpm

cheers,
GAZ

[MikeKP61]

I wouldn't mind but it bogs down on roundabouts and corners at low speeds too, I don't want to shit the clutch letting it in at high revs

[Tankie]

If it's bogging down can you lower the needle,
that's the one in the slide,
this will lean it from above idle to about half revs.
The fitting of the exhaust has changed the tune of the engine, if it's not "on pipe" it will appear rich
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2,000rpm on a 125 2 stroke, are you serious?

How much torque and power are you expecting from a 125 T2 at those revs? It probably makes around 3bhp max at that point.

Tyga claim about 4bhp at 4300rpm on an RS125 Aprilia with one of their pipes, bhp below that isn't even worth bothering with.

https://tyga-performance.com/images/00psm/02tpfitman/02fitmanaprilia/02adynoaprs125.jpg

https://tyga-performance.com/product_info.php?products_id=952
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[Tankie]

Also make sure the reed is sealing off, this is what gives this engine low revs torque.
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[stirlinggaz]

Hi,
Its a characteristic of these "sports/race" type exhausts, to sacrifice power lower down in the revs, shifting the power band up a bit (& sometimes narrowing it) & increasing bhp to around 21kw @ 10500-11000rpm
Whereas the OEM exhaust (a 15kg lump of scrap metal imho) sacrifices power for usability at lower revs but tbh i can't recall EVER riding my nsr at below 5000rpm, except when setting off
Have a look at a dyno print for a jc22 fitted with a tyga, giannelli etc & you will see there's very little power to be had below 4000rpm, although some pipes are worse than others.(I prefer the jolly-moto)
A happy medium can be had by fitting a bigger carb

cheers,
GAZ

[Tankie]

A happy medium can be had by fitting a bigger carb
No! total shite!
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[MikeKP61]

[stirlinggaz]

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[P.]

I'd never attempt to use 2k rpm for anything on a 2 stroke other than idle speed.

I never used to pull away on my RS under 5k, slipping the clutch to push those revs up. 2k is absurd

Even my KH125 which is a low tuned commuter 2 stroke was dancing at over 3k when pulling away. Use more revs.

[alains]

i said many times before BOYSEN reeds are not well adapted for the NSR (too hard , only 2 petals) . the best make are the jollify 36/100 mm , cheap and long life
they can be purchase https://www.ebay.de/itm/JOllify-Carbon-Membrane-fur-Honda-NSR-125-R-036e/120762901399?hash=item1c1e07a397:g:r-gAAOSwZkJURggn
your jetting are OK , but you may have a problem with your choke
the choke piston has a concave rubber underneath which close the hole . if for any reason it doesnt close properly when you adjust the pilot screw it's possible you unscrew at the end
if the spring is worn , cable with sharp bends , choke body durty you will have the same bugs
good luck
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[MikeKP61]

I'm not trying to "kid" anyone, I'm asking a question and looking for a solution (something you haven't given). If you read what I said I mentioned it also bogs down on roundabouts and slow corners also, I'm looking for a fix to bogging down at low revs. I have NEVER ridden a 2 stroke bike before this oh holy 2 stroke master if you must know, I just like the idea of them so I picked up one in a shite state and rebuilt it to have something to mess about on. Have to start somewhere and all that, maybe in a couple of decades I'll be as pig headed as you

The exhaust is for the 150SP but I was talking to the guys at Tyga and they said it should run fine on the 125 with a few mods like up jetting.

I'll have a look at the choke Alains and look into them other reeds too, thank you for your help, I'll let you know how it works out!

[P.]

So you've never ridden one before. They need revs. There is next to zero power at all in the bottom 1/3 of the rev range. You need to keep them higher up. Pulling away needs revs.

Stop being such an ignorant turd and listen to the advice.

[Tankie]

Paddy is right, the reeds do make the engine more flexible but the engine must be revving a bit , it is a completely different to how a 4 stroke behaves, where it will pull right through the rev range
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[MikeKP61]

Thanks for your help everyone, I'll figure it out.

[rhys99]

[MikeKP61]

You don't seem to understand, say when I'm coming on to a round about and I'm I'm second gear, when I throttle down up to the roundabout it's slows the engine grand, but when I open the throttle again at say 3k to 4K revs it bogs down. If pin the throttle opens ot I'll pick up again but it jolts into action like when you have a loose chain. If I was to just keep the throttle where I normally keep it, say on my Hornet (4 stroke I know sorry) it will just continue bogging and die. I wouldn't mind if keeping it at 5k revs the whole way around the round about in first was feesible but it's not how I'm used to riding. Is it a matter of Justin using it and figuring it out or can I adjust the carb to give a more even throttle change from idle to cruise?

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[P.]

Try and keep it close to where power comes in, definitely above 6k, pulling away at decent rpm and cornering at 6k+ and popping the throttle open still may give you shit though... you'd really want to keep it on the boil so where the power starts.

It is made to be thrashed anyway.

[alains]

paddy !!! bla,bla,bla
better say Nothing than that

mike dont forget that the full power cant be reached prior at least 5mn warming and that all 2 strokes are a bit painfull from 3K to 7K this is why i recommand these jollify than boysen
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[P.]

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