NSR250 rebuild - 'The ELF Special'

**Wil_K** · 27th July 2013, 10:21

Originally Posted by speights_bud

Can't remember if i posted in here a while ago or not.

Anyway, got a set of MC16 fairings here, (minus front guard). pretty good nick just need a paint where they've been sanded back a bit by previous owner.

$150 take em away. I can bring to manfeild next round of winter series or we can work something out.
Can probably chuck in the original moulded indicators for the front and maybe the wing mirrors if i can find them

Would prefer to see someone using them than collecting dust in the shed. That and I'll be a track official at the MotoGP in Phillip Island and need the $$ to buy the sign written "official" wet weather gear.

That's a decent price for those fairings, but I'm still gonna move away from the original MC16 bodywork to some RS stuff.

**speights_bud** · 27th July 2013, 11:05

cool as, i'm open to offers if anyone is keen

**Wil_K** · 1st August 2013, 19:30

Small update. I think I have solved the problem of the plug fouling. I noticed that the upper cylinder was misfiring. The misfire was very bad at idle and low rpm, but would improve as the revs picked up. I initially thought electrical, so I tried swapping the coils, but this made no difference, and neither did a new plug. Battery is brand new and fully charged. I reset the idle screw to factory settings, and re-synced the carbs (visually) as I had been fiddling with these settings to try get things to improve. The changes made a small difference.

I figured it must be fueling so I pulled the carbs off again, a bit of an annoying job with the oil pump attached. Carb settings were as I left them, stock standard. Also, the air filter is brand new. I then checked the air correction circuit connections for blockages. No blockages, but I noticed something I had missed when installing the system. The 4 way connector has a small brass jet on the of the connections to restrict flow. I looked at the diagram in the manual and I believe I had the wrong hose attached to this connection. Swapped a couple of hoses around and put everything back together.
Huge improvement! The exhaust pulses now feel consistent out each muffler. And there is the same amount of smoke from each side too. Misfire is gone. Still, I only took it for a 5 minute ride. I'll see how it starts and runs tomorrow morning.

**imdying** · 2nd August 2013, 12:19

Successs

**Wil_K** · 8th August 2013, 11:21

Originally Posted by imdying

Successs

Not quite. I fixed the misfire, but it's still killing the top cylinder plug every time I start it. I'm thinking you could be right about the weeping float valve, I'll be replacing them. I also noticed the needles look quite worn, so I'll be replacing those too.

**Wil_K** · 14th August 2013, 21:45

Picked up these carb rebuild kits from ebay. $26 US for both!

Replaced the needles, float valves, air screws and gaskets with the ones from the kit. Slow jets and emulsion tubes are different from OEM so I left the old ones in. I've also put in 140 mains to be on the safe side with the modified airbox lid and aftermarket pipes I'm running.

The bike now runs much worse! It won't run for more than a few seconds, and that's only on full choke. Only one cylinder seems to be firing (the problem cylinder). I'm guessing the needles which are not the same as the standard MC18 ones are now completely blocking the main jet at idle/low throttle, and my pilots are too small to supply enough fuel. Either that or I created an air leak somewhere when reassembling the carbs. I've ordered pilot jets in the next two sizes, so I'll see what happens when I fit those.

These motors are so damn sensitive!

**Neal** · 16th August 2013, 14:03

On a stock motor you normally run 38 pilot jets and with some tuning sometimes a 40 . Compare the lengths of the needles , if you we're able to find adjustable needles in the past you needed the emulsion tubes to go with them as they were longer . I had a friend that used a shim to raise his needle .

**speights_bud** · 16th August 2013, 17:13

Yep we use 0.5mm shims on the NSR to adjust the needles as we don't have the adjustable type. Sorry i cant help with Jet sizes as we are running the bigger carbs, chambers etc.

**Wil_K** · 16th August 2013, 18:13

Ok, so I've put #42 pilots in, which seemed to make a small difference. I then screwed in the right hand airscrew almost completely and the bike will hold an idle and rev without choke. Things are still nowhere near right though. I managed to take it for a ride but there's just no power or torque anywhere especially down low. I did eye up the needles and they look the same length, I suspect they are probably a slightly different taper design to stock ones though. They look more like MC21 needles as the MC18 ones are brass. I'll do the shimming technique next and see what happens, and also measure the needles properly with a caliper.

**imdying** · 16th August 2013, 18:29

If you have richened the pilot circuit up that much to make it run, perhaps it's not able to draw anything at all from the main circuit? Maybe a blockage? The emulsion tubes are all clean?

A friend has a whole heap of needles (HRC and OEM Honda), I think he has a spreadsheet of all the lengths and dimensions, if it interests you.

**Wil_K** · 16th August 2013, 19:22

Originally Posted by imdying

If you have richened the pilot circuit up that much to make it run, perhaps it's not able to draw anything at all from the main circuit? Maybe a blockage? The emulsion tubes are all clean?

A friend has a whole heap of needles (HRC and OEM Honda), I think he has a spreadsheet of all the lengths and dimensions, if it interests you.

Emulsion tubes and airways all seem very clean to me. I'm pretty sure the problem is the needles. I mean it was running rich on the old ones, and now it's the complete opposite. I would have bought OEM MC18 specific needles, but they are so hard to find and the one place selling them online was going to cost around $160 NZD shipped for a set.

That spreadsheet does sound like it could be useful. Does your friend also have some Mc18 OEM needles?

**Wil_K** · 16th August 2013, 21:02

I pulled the needles out. The new ones are the same length as the old ones but they seem to be a larger diameter at the tip. New needles measure 1.35 mm at tip just before it tapers to a point, and the old ones 1.15 mm. Sure the old ones must be a bit worn, but I doubt they were 0.2mm larger when new.

**Drew** · 17th August 2013, 10:25

If it was the needles, I would expect it to run fine once you picked the throttle up at all. Assuming that the were bottoming out in the jet because of the wrong taper on the tip.

If not run fine, at least idle on two pots.

Do you have another set of carbs?

**Wil_K** · 29th August 2013, 10:46

Forgot to mention, I've got the bike running quite good now. I've got the standard needles in, and #42 pilots.

It sounds crisp and clean, and revs out nicely. The only problem is: no bottom end torque! I have to really slip the clutch a lot to get it moving. Even with the large pilots and air screws screwed in quite far, It is still a little lean down low. Ie. no low end torque, and difficult cold starting. Adding a touch of choke instantly brings back the bottom end torque confirming the leanness.

I decided to replace the rubber intake manifolds with a spare set, as the old ones had some cracking around where the boost bottles connect. It seemed to make a small improvement to bottom end torque and eliminated an odd flat spot at around 5k rpm. Still ain't right though.

I may try adding a light smear if liquid gasket to each side of the reed block gaskets just incase an air leak is present. Otherwise I'm lost as to why my bike requires such rich jetting. It seems the consensus is #42 pilots are about as big as you go on highly tuned NSR's and mine's only got aftermarket chambers, and a derestrictor. Or maybe this bike is an exception, and needs #45's?