NSR250.net Forums Logo: Honda NSR 250 Forums, Classifieds and Service Manual in English. Covering All Honda NSR 250 MC16, MC18, MC21 and MC28 models
NSR250.net Forums

#
 
#
 
Performance Engineering

  • NSR250 Forums Index ‹ NSR250R Discussion
  • Members Content
  • Members Garage
  • Subscription
  • Transactions
  • FAQ
  • Search
  • Register
  • Log in

Premix jetting question


Reply to topic   printer-friendly view
Page 1 of 1   Download Topic





bj

 
Posts: 16
Joined: 19 Oct 2006

Location: Sydney AUS
    Send private message View user's profile
    Reply with quote  

Premix jetting question

Thu Oct 19, 2006 5:59 am » Post: #1 » Download Post

Guys

firstly i'd like to thank the people who helped me about 2 months ago with my post about the RC valve removal (posted under a mates login). got them out fairly easily once i figured out what i was doing! the hammer claw worked a charm Wink

now, after much waiting, the time has come to rebuild my baby after the rear cylinder shat itself at the track, apparently due to detonation. I'm thinking about going to premix, and i just want to ask about the jetting. I've had a look around on the forum, and whilst the info is helpful my question is a little more specific

two questions:

Is it worth it? the bike is a 50/50 road-track bike. i've got a 600 to get around on, the NSR will only see street action when i feel like annoying the local residents and my 4 stroke owning mates Twisted Evil. So i'm not worried about having to carry some oil to mix every time i fill up.

and secondly, what i really want some help with. I'm planning to go 30:1 fuel ratio which seems to be the standard, is there a rough guide i can go by to increase my jet sizes to keep a good air/fuel ratio? Or is it a play it by ear thing? Am i better to wait until i can afford take it to a mechaninc and get it dyno'd and just run is standard for now?

I don't know much about it's history or setup, i bought it from a dealer, but it's running no airbox (pod filters), rear head on the front, and seems to have been jetted to suit.

thanks in advance!
Back to top


fontyyy

 
Posts: 3509
Joined: 10 Apr 2004

Location: Derbyshire, England
1991 Honda NSR250 MC21
    Send private message View user's profile Visit poster's website MSN Messenger
    Reply with quote  

Thu Oct 19, 2006 1:52 pm » Post: #2 » Download Post

Personally I don't see why you'd bother with pre-mix, it's a lot of hassle for little (or no) reward.

Make sure it's jetted properly first before you worry about anything else, just the fact that it runs only means it's quite near, it doesn't mean it's not a couple of sizes too lean and going to seize someday soon anyway.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread
Back to top


StephenRC45
Site Moderator
Site Moderator
 
Posts: 4884
Joined: 28 Jan 2004

Location: Cornwall, England
    Send private message View user's profile
    Reply with quote  

Thu Oct 19, 2006 4:53 pm » Post: #3 » Download Post

Because it add to that "whats he doing" look at the petrol station,

First you pull up on something with no lights, sounds like a bag of nails and smells. Then for some reason measure some sort of liquid and put it in the petrol tank!? Followed by shaking the bike... after which you have to run with it to start the thing... then pulling away the same bag of nails clatting around with large amounts of revs and smoke, leaving the bloke whos filling the 4x4 up wondering wtf just happened there! Idea
_________________
If I have to take the carbs off once more...
Back to top


nsr.wayne
Supporter - Carbon
Supporter - Carbon
 
Posts: 1068
Joined: 30 Jul 2004

Location: Portsmouth,Hampshire.
    Send private message View user's profile Send e-mail MSN Messenger
    Reply with quote  

Thu Oct 19, 2006 5:55 pm » Post: #4 » Download Post

StephenRC45 wrote:Because it add to that "whats he doing" look at the petrol station,

First you pull up on something with no lights, sounds like a bag of nails and smells. Then for some reason measure some sort of liquid and put it in the petrol tank!? Followed by shaking the bike... after which you have to run with it to start the thing... then pulling away the same bag of nails clatting around with large amounts of revs and smoke, leaving the bloke whos filling the 4x4 up wondering wtf just happened there! Idea


TART ! Very Happy
_________________
Harley Davidson is the worlds most efficient way to turn petrol into noise without the harmful side effect of horsepower.
Back to top


cgallant
Site Admin
 
Posts: 1608
Joined: 18 Jan 2004

Location: Ocala, FL
2001 Honda RS250
    Send private message View user's profile Visit poster's website
    Reply with quote  

Thu Oct 19, 2006 8:09 pm » Post: #5 » Download Post

For the street? Stick with oil injector. Check your pump often and maks sure the feeder tubes havent backed their way off the nipples below the intake manifold.

For track? rip it off and go pre-mix. One less mechanical thing to **** up on you, as well as a slight weight savings. Oh and you can have a better selection of oils to use since the good ones shouldn't be used for injector systems.


As for jetting and stuff when using pre-mix, check out the other thread going at this very moment titled "PRE-MIX".
_________________
Charles Gallant
Back to top


bj

 
Posts: 16
Joined: 19 Oct 2006

Location: Sydney AUS
    Send private message View user's profile
    Reply with quote  

Fri Oct 20, 2006 3:48 am » Post: #6 » Download Post

Thanks guys for the assistance, been reading the pre-mix thread too

Whilst i'm getting advice, another Q:

the engine died on the track. took the cylinders off and the rear piston had kinda melted, the rings were compressed and sitting flush with the wall of the piston. Had to file away at it so i could get the piston pin out. The damage is i believe due to detonation, extreemly similar to this: http://pg.photos.yahoo.com/ph/rothmansmc18/album?.dir=f9ce. Only happened to the rear cylinder, the front was fine by comparison.

So, my question, what are the likely causes of detonation? It had BR8ECM spark plugs that are probably a bit hot for Sydney conditions, i bought it from a country town where there winters are much colder. cold days here are 15 C, there it can be lucky to get over 10 in winter. I was using a low octane fuel (91 RON), and rode it to work the day before it died in shocking traffic (10km trip=30 minutes), so it got more than a little hot.

Would using cooler plugs and higher rated fuel be likly to help solve the problem? i thinking about getting BR10ECM plugs, and using 95 octane fuel.

StephenRC45 wrote:Because it add to that "whats he doing" look at the petrol station,

First you pull up on something with no lights, sounds like a bag of nails and smells. Then for some reason measure some sort of liquid and put it in the petrol tank!? Followed by shaking the bike... after which you have to run with it to start the thing... then pulling away the same bag of nails clatting around with large amounts of revs and smoke, leaving the bloke whos filling the 4x4 up wondering wtf just happened there! Idea


hahaha i wish, NSRs and strokers in general are as scarce as hens teeth around here. I got it at a very good price (AUS $3000, about £1200), with a full years rego and insurance, but it's a MC21R, so no bag of nails Sad. The dealer even delivered it 400kms to my house, as he was heading to sydney anyway! I didn't buy it as a street bike, i've got a hornet600 for that, but i do take it out every now and then, just to keep the engine cycling Wink

Once again guys thanks for the help, this whole DIY mechanic thing is still kinda new to me! Carburettors was about the extent of it before this!
Back to top


StephenRC45
Site Moderator
Site Moderator
 
Posts: 4884
Joined: 28 Jan 2004

Location: Cornwall, England
    Send private message View user's profile
    Reply with quote  

Fri Oct 20, 2006 5:24 am » Post: #7 » Download Post

I would always use 95+ ron fuel and BR9ECM plugs (or 10's)
_________________
If I have to take the carbs off once more...
Back to top


fontyyy

 
Posts: 3509
Joined: 10 Apr 2004

Location: Derbyshire, England
1991 Honda NSR250 MC21
    Send private message View user's profile Visit poster's website MSN Messenger
    Reply with quote  

Fri Oct 20, 2006 10:07 am » Post: #8 » Download Post

For any given setup colder plugs and/or higher octane fuel will ward off detonation.
The bike just needs setting up to suit the fuel it's running and plugs that won't melt but there's going to be a max you can push it to (ignition/compression wise) for a given octane.
Hence you just can't get a '28 on an 010 card or a '21 on a race fuel cdi to stay alive on anything other than Avgas or proper race fuel.
I wouldn't have thought a normal full power NSR is ever going to be that happy on 91ron and BR8ECM's, road or track.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread
Back to top


castroljc

 
Posts: 82
Joined: 24 Dec 2005

Location: Northern Ireland,Belfast
    Send private message View user's profile Send e-mail MSN Messenger
    Reply with quote  

Fri Oct 20, 2006 1:22 pm » Post: #9 » Download Post

StephenRC45 wrote:Because it add to that "whats he doing" look at the petrol station,

First you pull up on something with no lights, sounds like a bag of nails and smells. Then for some reason measure some sort of liquid and put it in the petrol tank!? Followed by shaking the bike... after which you have to run with it to start the thing... then pulling away the same bag of nails clatting around with large amounts of revs and smoke, leaving the bloke whos filling the 4x4 up wondering wtf just happened there! Idea


i have to see this for myself sometime...
_________________
do i need an NSR to be a member ???
Back to top


Andy
Site Admin
 
Posts: 11950
Joined: 19 Jan 2004

Location: Devon, UK
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Fri Oct 20, 2006 5:10 pm » Post: #10 » Download Post

Laughing

StephenRC45 doing his silly wiggly dance at the pumps really is something to be seen!

Re: the original topic, I have to agree with Fontyyy, 91 octane and BR8ECM plugs is not only a combination I wouldn't ever consider running - I personally wouldn't use either full-stop! I had to use 95 in my 21 the other day, and even that made me think twice about what I was doing with the throttle and the load on the motor!! Smile
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.


Check us out on Facebook! Please "like" our page!
Back to top


pbekkerh

 
Posts: 656
Joined: 07 May 2005

Location: Denmark
    Send private message View user's profile
    Reply with quote  

Fri Oct 20, 2006 5:16 pm » Post: #11 » Download Post

It had BR8ECM spark plugs that are probably a bit hot for Sydney conditions, i bought it from a country town where there winters are much colder. cold days here are 15 C, there it can be lucky to get over 10 in winter.


The air temperature has nothing to do with what temperature range the spark plug should be, its determined by the internal temp. in the cylinder.

The ambient temp. for a cylinder is around 50-60 degrees C and is determined by the cooling system, which keeps the cylinder at a constant temp. at air temp. between 0-35 C.

Internal temp. in the cylinder is aroung 7-800 C and is determined by: way of use, octane rating of the gas and degree of tune.

The normal NSR should use BR9ECM and at least octane 95, a tuned might use BR10ECM, so the BR8 and the 91octane could be the reason for the seizure.

Air temp. does however influence the mixture ratio, but thats another story.
_________________
Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom
Back to top


bj

 
Posts: 16
Joined: 19 Oct 2006

Location: Sydney AUS
    Send private message View user's profile
    Reply with quote  

Sat Oct 21, 2006 2:31 am » Post: #12 » Download Post

thanks guys for the help! Going to give the BR9ECM's a go, and 95 octane fuel and see how she runs next track day at the beginning of december

Will to have a word with my mechanic, whos a good mate, and see if i can borrow their dyno for a while i think. going to leave it with injected oil till then.

and pbekkerh, thanks for the info, i was mislead by someone whom i'm now thinking knows less than they seem to believe

I'll let you all know how i get along! Once again thanks for the help!
Back to top


Reply to topic   printer-friendly view
Page 1 of 1   Download Topic

NSR250R Discussion

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum

  • NSR250 Forums Index
  • All times are GMT
Powered by phpBB © 2001, 2005 phpBB Group


Hosted by NSR250dotNET © 2008 NSR250dotNET