Gents,

Before I go final with my new carb install, I was wondering if anyone knew a ballpark setting for what I have:

I replaced my stock carbs with a cleaner/better set but the only difference I'm wondering about is plugging of the power jets in the float chambers. I put the original 38 SJ and 138 MJ with the stock needles. I'm also running a airbox with stock chambers/pipes/unrestricked ignition. Basically all stock. I know that the PJs are plugged by folks with mods (pipes, HRC needles, etc) so do I need to unplug them or just go a little bigger on the main jets so I don't blow up? At this point, I just want to run a bone-stock NSR for a little while before doing any upgrades so I have a solid baseline feel. Thanks!

Oh, and does anyone know if a stock CBR F3 front wheel bolts up to a MC21? Not exactly a big mod but just wanted to know if I can easily start running 120 fronts for the future.

Jae

pekingduc1@gmail.com

Have you opened up the airbox? I would recommend 4 x 20mm holes in the front slope of the lid for best results.

Blanking the PJ's can make setup on a race bike easier, as you can just concentrate on the mains, but on a road bike they generally tend to give you a slight margin of saftey. In very basic terms, the higher the RPM, the more fuel drawn through the PJ's (and hence a richer mixture). High RPM and weak is BAD... high RPM and rich is not so bad - you just lose a little power!

If you haven't modified the airbox, then I expect 138 will be too rich. If you have modified the airbox, I wouldn't be surprised if 138 was still too rich, but you will never get me quoting jet sizes.

No idea about the CBR wheel. Anything can be made to fit (probably better off looking for an NC30 front wheel), but why bother? In my experience an NSR with a 120 front tyre steers like a pig. The stock tyre sizes work the best.
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Andy.
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Thanks Andy. My airbox lid is stock but I was thinking of either buying the Tyga modded lid or just drilling big holes like you mentioned. So if I do that, it sounds like sticking with the 138 MJ will be alright even if it is too rich (safer is better right?). The bike will see a few track days soon but I won't be hitting any really long straights so I'm more interested in crispy throttle and good drive (relatively speaking for 2-strokes) out of corners. Besides, I'll be swapping between the NSR and my NT650 so the stronger my midrange, the easier the transition between both bikes. Thanks again Andy.

Jae

Of course it all depends on where you are and the conditions. Richer is safer, but too rich can sap a lot of power. You will need to do a "plug chop" to give you an idea on how close the jetting is.

A size or two too big (132~135 for example, IF 130 is the ideal jet) will not cause you too much trouble, but more than that and the power will noticeably drop off.

Remember: It's better to be one or two sizes too big than one size too small!
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Andy.
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I hear you but I'm having trouble locating a "safe" place to do a proper plug chop. I don't know of a good area to do 6th gear WOT for at least 10 seconds without going to jail. And even if I save it for the track, our straight there is maybe 6 seconds long. I guess going WOT without any load (staitionary) is pretty much useless right?

Yep, it needs to be under load. But, the "run flat out for 10 seconds" is more than a little bit extreme and ironically unless your bike is pretty close to spot on (or rich of course) it probably won't last that long.

But if you're confident it is OK get it up to flat out in 6th and as it just pulls the max it will (preferably up a slight hill, don't worry about the 10 seconds flat out) hit the kill switch and whip the clutch in. Get the plugs out (both of them) and have a look.
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That's good to know. I figured most guys didn't do a full 10 second blast. I also realize that maybe at least some of you would do a plug chop while on a dyno. Since my bike is pretty much stock, I ordered some 128 main jets. The only thing I've done so far is drill some holes into the airbox lid and adjusted my oil injector cable (get rid of slack).

Just to be safe, I went ahead and ordered some additional sizes too since I'm not sure how "lean" I would be running stock MJs (128) on a plugged PJ setup. So, I bought some 130 and 132 MJs as well. Never looked into it yet but are the PJs easy to swap out or are they pressed in?

Don't go blanking the PJ's if you are only running small jets... it won't last long!

Blanking the power jets will most likely see you up in the mid 180's somewhere.
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Andy.
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That would explain why the carbs came with 180 MJs. So do the PJs only work in the MJ throttle range? Do I need to worry about adding washers to my stock needles as well for blanked PJs? If I install the 180 MJs back into my carbs, will I be in the ballpark jetting range even with everything else stock?

Is that 180s with the stock oil injection?
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Too rich for injectors? If it is, what's the recommended range of MJs for blanked PJs and stock injectors? I'm at pretty much sea level.

It won't be far off, it'll start and run.

Washers under the needles are for very fine tuning once your MJ is right.
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Ok. Once I get some spare time, I'll mess around some more but if 180 MJ is in the ballpark for me then I'll start with those. Worst case, I can always re-install my completely stock carbs and go with default jets.

Thanks again everyone!

Pekingduc