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| | |-+  Honda NS50 (AC08) Jetting and Carb (filter) size?
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Author Topic: Honda NS50 (AC08) Jetting and Carb (filter) size?  (Read 3098 times)
Heretic
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« on: June 04, 2010, 09:38:11 AM »

Looking for some advice here, maybe you guys can help.

-As far as I can tell the carb openeing is 38mm?  Does that sound about right for the stock carb, I don't have a micrometer, so I'm using a tape measure.

-what kind of jetting change am I looking at after fitting a K&N or Foam filter?

-What kind of jetting change after fitting a K&N and free flowing pipe?


Any help would be much appreciated.

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k.ham
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« Reply #1 on: June 04, 2010, 09:55:01 AM »

38 mm is correct for the air filter mount. 

What size of jet do you have right now.

you can pick up jets at agri sports for about $4 each.  As far as I know that's the cheapest in town.  if your modding the bike to incease it's air pumping capacity, then you need to move up in jet size.  

You probably have a 100 or 105 jet right now.  Standard on an NSR50 is 105.  Confirm what you have and buy the next size up in increments of 5.  that will get you close enough.  remember you're only working with about 8 hp.  This could be a lot of work to get you to 9 hp (but it's a great way to learn about your bike/motor and carb tuning).  But beware, it you want to race your bike in the spec class, then it's no mods other than air filter and carb/jet tuning and a braided brake line (if you have disk brakes).   You might get away with some suspension upgrades on an older bike.

You also need to consider the effects of engine/performance mods on reliability.  That an entire topic unto itself, but it boils down to your personal choice of wrench time versus riding time.



  

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Hawker
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« Reply #2 on: June 04, 2010, 11:03:50 AM »

I think that the older NS50's should be treated the same as the old YSR50's when it comes to modifications allowed for Spec Supersport.  Namely, you can upgrade suspension, exhaust, intake, and carb, but you can't do anything to the engine internals.  The whole idea is to bring them up to the level of the newer NSR50RR's without surpassing them.

Joe, you should run any modification ideas past the CNMRA rules bodies to see if it would be allowed.  The rule book states:

"  Note: in the interests of providing affordable and fun racing at CNMRA events, riders owning an older uncompetitive machine may upgrade that machine and apply in writing to the CNMRA for classification in a spec class. An example of this may be an YSR 50 fitted with a stock Derbi or Honda 50cc engine, when applying for classification of this unit for spec classes it must meet the specifications for both the frame and the engine according to the machine class rules. When petitioning for classification the rider must make the case for the unit to compete in the spec class of his/her choosing. The CNMRA reserves the right to place all entries in an appropriate class. "



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Heretic
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« Reply #3 on: June 04, 2010, 11:41:21 AM »

Yeah I agree, it's definitely at a power disadvantage.  It’s obviously tuned with street use in mind.   The pipe is really tuned for low rpm/mid range.  It even has a built in rev limiter.   I realize that just bringing it up to NSR spec makes it a cheater bike, kinda of a disappointment there.  Cry   If I could convince the CNMRA to also allow exhaust and CDI on that bike, that alone would go a long way to bringing it close.

But I have to say I really do enjoy it around that track, it an exercise in frustration on the street, but it makes so much sense at the track.  I’d definitely like to try racing in the future, just want some more track time under me first.   So I’m either looking at applying to the CNMRA to allow my NS into Spec with the mods done or buying a NSR/Thunder bike.  I would prefer to race the NS in spec. I guess there is always going 63cc Kitaco and racing up in Formula, but I’m not even sure how you would get allowed for that class without starting in Spec first.  But at least that class allows more mods.

If this bike gets negated to being just a track day tool, so be it.   Maybe I can rent a bike for one of the National events in the future?


I would also like to add, I never expected to be chasing power, but after my first time out there, there wasn't a bike out there I could hang with on the straights.  Not even the 100cc Thunder class bikes, and certainly not the NSR's.  It's seems like I'd be off the pipe on the limtier and they would just keep reving and pulling away.  Like a 50km/h mugging..  Tongue

« Last Edit: June 04, 2010, 11:44:38 AM by Heretic » Logged

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Heretic
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« Reply #4 on: June 04, 2010, 11:51:33 AM »

Also Foam vs. K&N style oiled cotton? 

Does it matter?

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k.ham
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« Reply #5 on: June 04, 2010, 11:58:43 AM »

I realize that just bringing it up to NSR spec makes it a cheater bike, kinda of a disappointment there.  Cry   If I could convince the CNMRA to also allow exhaust and CDI on that bike, that alone would go a long way to bringing it close.

I agree with Hawker's comment.  The intent of the CNMRR clause for upgrades for older bikes is to keep the playing field level in the spec classes and to allow older bikes the ability to be upgraded to the level of their more modern equivalents.  On that basis, I would expect that an exhaust upgrade would be permitted also.  Sounds like a case-by-case basis review of each request.    So if the request was accepted, it would not be a cheater bike. thumbs

This may be an over-simplification, but the carburator jet size you require for a modded bike really represents the degree of the performance upgrade.  So if you undertake mods on your NS50, you would want to land close to a jet size of 105 (consistent with a stock NSR50).

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k.ham
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« Reply #6 on: June 04, 2010, 12:02:39 PM »

Also Foam vs. K&N style oiled cotton? 

Does it matter?

probably doesn't matter.  on my NSR's, I've got a mix of K&N's and those fine stainless mesh (cone type) filters (purchased on ebay and shipped from china).  Either type seems to work fine.  I don't have any foam ones, so can't comment on how they work.

Some people run open air (no filter).





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Heretic
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« Reply #7 on: June 04, 2010, 12:06:19 PM »

Thanks for the help guys, I appreciate it!

Yeah jetting wise, I just don't want to melt anything.  2 strokes make me nervous in that regard.   No airfilter?  I don't know it's pretty dusty out there.  I guess maybe on race day?  dunno

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Heretic
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« Reply #8 on: June 10, 2010, 02:51:38 PM »

My K&N hasn't showed up yet, but with the airfilter off, when you go WOT it revs really nice (loud!), you can clearly feel it come on pipe as the RPM's go up, and then it's pulling great almost a surge of acceleration, then it just flat out stops reving. It feels like it hits a wall, Sounds like a rev limiter.

DaaaaDaaaaaDaaaaaaDaaaaDaaaa

The new racing CDI is in, so I know it has no built in rev-limiter. So is that just too lean main jet with the air filter off? Or is this a problem with that new CDI?  Shouldn't it just fall off power, and taper off now?

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k.ham
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« Reply #9 on: June 10, 2010, 04:03:28 PM »

did you adjust jet size for the open air carb.

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Hawker
Brent M.
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« Reply #10 on: June 10, 2010, 04:58:20 PM »

The quick burst you describe is from the engine leaning out a bit just before leaning out too much.  Throw a fatter main jet at it.

Just remember, though, that on two-strokes lean=fast, but too lean=holes in pistons.



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Heretic
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« Reply #11 on: June 10, 2010, 06:13:35 PM »

No I haven't changed the jet yet, I just wanted to test that the CDI unit was wired in right.    I have little K&N style filter coming in the mail, so I was planing on jetting after that shows up.

I'll pull the carb this weekend, find out what main jet is in there now and go get 1-2 bigger one (+5,+10?) from Agrisport.  These are Keihin carbs on these bikes right?  Does Agri-sport stock the jets for these things? Is the needle height adjustable on these things?



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k.ham
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« Reply #12 on: June 10, 2010, 06:38:08 PM »

Take the main jet out and take it in to Agri-Sports.  That way they can match the style and thread.

First step is to dial in the correct jet size for proper air/fuel mix at midd to full throttle.  Once that is good, you can work on needle height to tune for throttle response from idle to mid throttle.

"IT'S JUST THAT EASY" thumbs

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Heretic
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« Reply #13 on: June 11, 2010, 08:49:23 AM »

I ryke it!

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Hawker
Brent M.
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« Reply #14 on: June 11, 2010, 09:08:43 AM »

Jets are cheap.  Buy several in increments of 5 so you can test a few without having to run back to the store.  Once you have is dialed in, you can buy a couple more in in plus/minus 2.5 (if available) to fine tune it.

Make sure that the needle clip is in the middle position before you start all of this.  Hopefully it's the adjustable kind.  Some aren't, and if that's the case you may need to order an appropriate needle.

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