Nsr 125 misfiring/spluttering

[Farmingstock]

After the rebuild I thought I'd start another thread with this question.

Right the bike is run in now for anyone following the previous thread.

However

The bike is misfiring and spluttering through the revs but mostly from 7000 upwards, I did run out of fuel a couple of times so though I better clean the carb and at the same time upgrade the jets.

The jets that are in the carb are:

52 - slow
70 - power
135 - main

The ones I ordered are:

65 - power
42 - slow
138 - main

The plug is perfect colour although I have bought another to use once the carb is back together.

Would the bike be faster with smaller jets in and would this make the bike misfire?? Seems strange with the plug being a perfect colour and not wet at all?

The carb is a dellorto phbh28fs

[Fin]

here is Alains' file, he has recommended jetting in there.

The ones you have bought are the recommended ones for a performance exhaust, should still be ok though.

[Farmingstock]

[stevo as b4]

Just don't downsize the main jet though, as your likely to end up sat on your arse well before 90mph if you do.

[Kickstart]

[Farmingstock]

hmmm could it be the carb/jetting that is causing the misfire? Or is it more likely to be an electrical fault?

It could be that the main jet is too small but the bike starts on the button every time and tickover is perfect, just The misfiring that's the problem which in turn isn't helping the performance.

Not sure if the exhaust is aftermarket or not, the bike is noisy, no stamps on it, not stainless, I changed the baffles in it, didn't look anything special.

I thought with the plug not being soaked ect that the electrical side of things should be ok?

I'll try the new jets in over weekend and see if Theres a change. I let a couple of others ride the bike recently to get another opinion and they both said, it's nearly there just not quite right some how.

Probably need a rolling road to be certain but there are none locally.

[Kickstart]

Hi

Main jet is the ultimate limit of fuel flow. Hence pretty much only relevant at full throttle or close to it.

If it is doing it at lower revs then probably not the main jet.

The NSR doesn't have a particular tough ignition system. For the basics check the coil, HT lead and plug cap (and that it is well connected).

Can you put a photo of the exhaust up? Someone might recognise it.

All the best

Katy
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Farmingstock]

Had the carb ultrasonic cleaned fitted new seals and jets to the carb, new plug need to get my multi meter to check the coil ect but checked the powervalve control and that seems to be working as it should. But it's still the same its kind of a spluttering and it doesn't Rev out.

Next step check the coil but after that any other ideas?!?

[Kickstart]

Hi

Not just the coil, stator as well, etc. After that check the reed valves are sealing (although they would probably cause more problems at low recs first), , etc

All the best

Katy
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[stevo as b4]

I'd get the coil and CDI and the stator pick up etc all checked out before changing any jetting from standard if your bike is a full power spec that is?

When you say the power valve moves ok. I'd that you turning it manually with pliers with the cover removed? Or are you checking for the full range of movement from the servo motor when it's both connected to the valve and with it disconnected from the cables?

And for jetting changes if you know 100% that the existing jetting is correct for a standard bike, you need to go to a two stroke friendly dyno.

Im a firm believer in that you or I would at best only be able to decipher between jetting that was so lean it will probably sieze the first time you go WOT or jetting that's so rich it's just fouled the plug.

That's all reading sparkplug might be able to tell you with modern fuels, and it's no more help than that.

Also you can go from very lean to very rich in one dyno run as you go through the Rev range. My dyno print is a very good example of this.

[Fin]

What clip is the needle jet on?

[Farmingstock]

[Farmingstock]

[Farmingstock]

Think I've cured it!

Not holding my breath but seemed much better.

I took the tank off and the tap, cleaned the tap and reserve out with an air line (there wasn't any dirt in there that I could see but still cleaned it up)

The coil tested fine (to manual spec) but the terminals wernt totally tight, not loose, but not that tight either, anyway I crimped them up a bit whilst I was there.

The bike feels much smoother (slower) not as punchy when it comes into the powervalve.

But

I'll go for a good run and see how it is!!

Oh yeah the clutch felt like it was starting to slip!! FML

[Farmingstock]

The bike is Reving round freely to 11,000 rpm in the first 4 gears now and feels much better.

Should it be Reving to 12/13? As it feels like there is a limiter at 11,000 or it just won't Rev anymore than that!!

Which way does the powervalve turn to open looking at the side of the barrel? As there is still some movement either way once adjusted and I'm thinking they are not fully opening!!

There is a slight water leak coming from the head, there is no gasket available from Honda so I may have to make one!! Has anyone else had this issue?

Cheers

[Kickstart]

[stevo as b4]

What is making you think it should rev past the red line?

The power should die before the red line on most two strokes as you don't get lots of over rev like say you would on a 600cc four stroke sports bike.

Most two strokes don't have any sort of hard cut rev limiter, so you are right there in a way, but I bet if you could look at a plot of the ignition timing map, you'd find that the timing retards once past peak torque and by the red line it could be sparking as little as 4-5deg btdc, which though it is set up like that for a reason, it obviously means you won't have much of a bang at those Revs.

I'm just learning about two stroke ignition systems and thier tuning, and how you set up the timing over the Rev range has a huge effect on the way the motor performs. So much so that to suit a different pipe you might well need to change the timing to get the most from it.

That's why I've bit the bullet and gone for a programmable CDI for my KMX.

Good to hear your making progress though and it hasn't blown up so you must have done something right too.

[Farmingstock]

Thank you for the replys, much appreciated!!

I have seen some YouTube videos of nsr's Reving past 11,000 and mine will literally not go past that, so just wanted to be sure there was no other tuning I could do?

When the powervalve is fully open, there is still movement left, which I think may be holding back some performance?!?

Thanks again.

[Burnzy1989]

Ok if you feel it's not opening fully you can all ways disconnect the cables at the servo motor and then turn the power valve open and use a nut to jam it fully open . You will have a flat spot at 7k up to 8 k and it should kick off like cat jumping from a cucumber 😂😂😉. And see what it is like .

I had to do this as my cables snapped and iv been ridding h mine for 2 months this way waiting for a replacement. I would say its ok for me as I ride on the pipe all the time u less in town and it's ok below 6k . But for some reason 7k is a dead zone no pull just boggs so ve aware of that . One thing to watch is that your bike can miss due to over richness on the main jet .

Best pipe for the nsr is one made by Romeu Henriques from Portugal . Easy to jet as u normal just need a 140 to 143 main jet standard pilot or 65 pilot and lift the jet needle .

[Farmingstock]

I may try this!!

I have tried adjusting the powervalve so it opens fully but still made no difference.

The bike will Rev straight round to 13,000 when its in neutral but will only Rev to 11,000 when I am riding it?!? Is this some sort of restriction???

I thought it should Rev as much riding as it does in neutral?!?

[stevo as b4]

There will probably be less than 10-12bhp made at 13000rpm, and yes it's normal for non rev limited engines to rev higher under no load than they will under load, it's common sense.

The porting, exhaust and ignition all dictate where the power will be made on a two stroke, a 1000rpm or so over either side of this peak the motor will be making hardly any power at all.

If you were to put this bike on a dyno it would tell you so many things about how it's running, fueling and were the power is and isn't made.

[Kickstart]

[stirlinggaz]

Hi,
No point in trying to rev it to 13000rpm (whilst riding) anyway, seeing as there's no more power to be had after 10500rpm

cheers,
GAZ

[Farmingstock]

Right thought it was better but it is actually worse!

I moved the throttle clip down one so one of the bottom and the bike ran much better lower end but once I get to around 9,000rpm the bike kind of has a limiter and just splutters and misfires till I change gear!

Pretty much every time I do this the bikes revs will die and it will eventually stall and won't start again for a while! I went 1/2 mile before and it stopped 3 times in that distance!! This was Reving it so it misfired!!

I have tried to book in for rolling road but they aren't interested!!

Anything else to try?

[Burnzy1989]

Ok N0 1 you need to check and give us ur cdi part number and power valve number .
N02 check your ht lead and cap and check all your wiring conections for green corosion and ur coil and stator and pick up .
No3 do plug cop at 9k rpm when it's missing and see what the plug is telling you and post it on here .
No4 what is ur air filter like and have u ever cleaned it .
No5 did u gap your piston rings when you built it up .
Have u got a gopro and film what it's doing