Jetting

[shnalln]

You know what makes jetting so confusing? All the contradictory information that's out there!
As mentioned in my other post, stock, the bike ran alittle rich, had alittle spooge, and wet plug. Stock it has a 380 main, 32.5 pilot, 30-74 needle, w/as 1.5 turns out. I'm at 1300 ft. asl, and temp has been around 70-90 deg. Right inbetween the manuals jetting change specs.
I changed the main to a 370, and turned the AS to 1.75 out. I think that the 370 will work out good, I opened the bike up today, and it feels reall smooth at full throttle. I did not get a chance to tinker, but I did get a good feel for whats happening. The bike has a slight hesitation off the start indicating a lean condition, I think this could be solved with with an airscrew adjustment. From about 1/4 to half the bike crackles/ rich.
I'm confused on the needle, if I change the clip position and make it leaner for the 1/4-1/2 throttle pos, wont it worsen my hesitition? I assume that the needle numbers correlate to the size of the different tapered, and staight sections of the needle, but but what does the 31 mean on a 31-75 needle? And the 75?

 

[shnalln]

Tried to edet but it wont let me, so let me clarify my question. How does a 31-75 needle compare to a 30-74?

 

[shnalln]

Ok, well I guess if I would take more time to read my owners my owners manual I would know that a 31-75 is one clip position leaner than the 30-74.

 

[Faded]

Actually its a half clip position leaner than a 30-75 which will lean it up between 1/8 and 3/4 (if I remeber correctly). The last number is the straight section of the needle. As far as I can see from what the manuals say there isn't a change in the taper of the needle, the only changes are in the straight section (74, 75, 76...) and the height (clip position, and the 'half' clip position - 31-xx vs. 30-xx). Another thing is that they don't provide any information on what effects the needle jet, or nozzle has (s-9 stock).

 

[shnalln]

Well I've got the 31-75 on order, it should be in this week. I still had some spooge with the 370, and since I was rich in around 1/2 throttle, I went on ahead and raised the clip position on the 30-74 to the first pos. and threw in a 360 main. We'll see how that does, I think either way, I'll probably use the 31-75 so that I'll have more versatillity with the clip taking into consideration temp changes here in Ks. The 74 does refer to the straight diameter like you where saying at 2.74mm so the 31-75 should be 2.75mm. So I think, if I understand this correctly, the 31 should have something to do with the taper, the 75 being leaner than the 74? If I'm reading this right, and you follow the chart in the manual, a 31-74 is a 1/2 clip leaner than the 30-74 so the 31-75 should be right around a full clip? I'm not sure, Anyway, theres plenty of room for me to go richer on these clips since they have five pos. but I won't get any leaner with the 30-74, so maybe the 31-75 is just what I'm looking for. I hope!

 

[shnalln]

Ok, I see what your saying Faded, the owners manual for the bike, says that the 31-74 is a half clip leaner than the stock 30-74, that makes sense, so the 74 refering to the straight section being 2.74mm and the 75 being 2.75mm. Yea, ok, well...I've got that down it's saying here that the straight section affects the throttle response so that will worsen my hesitation from start. Hmm...should have got the 31-74, oh well, I bet I can get enough out of the air screw to richen it up, maybe it'll be good. We'll see! Thanks alot for your input and setting me straight, I appreciate it!

 

[Faded]

No problem. People here (@4700 ft.) opt for the 31-75 needle and retain the stock s-9 nozzle and have good results. Not sure if this will work with your elevation, might be lean. Check w/who you ordered your needle from, they might exchange it for the right one if it doesn't work out. My dealer did this for me, it might be worth a shot if it makes it worse @ 1/4 throttle.

 

[shnalln]

Yea, 1/4 throttle isn't where I'll have the problem I don't think, I need to lean out 1/8-1/2 anyhow, I think that the 31 will do good at that, I'm just worried about that first 1/8 where I'm getting the hesitation, It's real slight with the 74 at 1 3/4 turns on the airscrew so the 75 may be a bit too lean. But if I can get it set with at least one turn on the airscrew it may be just right. That way all I've got to do when it starts cooling off is richen it up alittle, if all goes right. I still haven't got that other needle in, but like I say, I raised the clip to the first pos. with the 30-74 so I'll take it out this weekend to see how it does. My guess is that it will be really close, I hope...next thing will be to tear it apart and regrease, maybe think about acouple mods (MXbonz) airfilter kit and such. Well, thanks again FADED, I apreciate it!!!!!

 

[Faded]

Originally posted by shnalln
maybe think about acouple mods (MXbonz) airfilter kit and such.

Can't go wrong there. After trying a couple different air box 'fixes' I settled with the MX Bonz kit. It works great! :thumb: Let us know how that needle works for you once you get it in. Take care.

 

[shnalln]

I'll be going with the MXBonz kit too, Looks like a good set up.

Took the bike out yesterday...Before my clip change with the 370 main...well you know...BUT NOW...with the clip change and the 360 main, and I turned the airscrew in a 1/4 turn so it's now turned out 1 1/2 turns, this thing is a BEAST! It'll get on the pipe like nobody's buisiness! This bike was tame before! It no longer is a bike that can easily be ridden in the woods! WOW! I think that there is still some fine tuning to do, It may do just a bit better with the 31 needle...it's hard to say. Sometimes there was a slight (very slight)hesitation going through the gears, and other times there wasn't. I think that this phenominon is primarilly due to the fact that it's a fast bike in the hands of a slow rider! Remember I havn't riden in about Ten years, it doesn't apear to be too lean by any means. the plug is burning real clean (no white, grey, or that thick black sludge built up on it like before). This bike is now what I expected it to be! Thanks everyone for your input!
Well, we're going to a private track today, I've got tons of technique to work on, so again thanks to you all for your input, it's highly appreciated!

 

[motometal]

did you put the 50 tooth rear sprocket on yet?

 

 

 

[shnalln]

Fifty tooth rear sprocket with the stock front sprocket? Well....no not yet, I'll keep that in mind though, thanks! Been wondering where you were though Motometal! I have a new clutch perch, and handle bars to invest in after the weekend. Those damn gyro physics of the rear wheel, and a lip on the face of a jump ate my lunch this weekend (Got alittle nose heavy, need to remember to hit the gas when that happens!). I do have an older YZ perch that my budy and I set up that is working, but my bars do have a bit of a twist! (Not bad though) So a good pair of TAGs are my next investment! Depends on how long it takes my thumb to heal too (it didn't seperate, but it did fracture) Doc seems to think it should be good to go in about a week? I'm thinking two, based the finger that I fractured about a month ago! String of bad luck! That's the game, and that jump didn't get the best of me either! I hit it three more times successfully after the crash and burn! Don't get any better if you don't push yourself! My buddy was real impressed with the responsiveness of the bike, I still think it can get better, I think that if it was 80-90 deg, it would be spot on. (it was hotter than that this wkend though 100+) It's hard to ride in that heat anyhow, so I may just leave it!

 

[Faded]

shnalln,

Yes, 49 or 50 tooth rear makes a big difference. Don't worry, I'm on the injured list as well. Two cracked ribs thanks to a tree stump followed up by some knee surgery. I'll be a while before I ride as well. Get better soon.

 

[shnalln]

A rear sprocket change may come in the future, I'll decide on that when my technique gets a little better. After ten years of not riding, this bike can prove to be a handfull at times just the way that it is! The power is definately enough to haul me around as fast, and most of the time faster than my skills will allow! So for now, I'll just concentrate on developing my technique and breaking myself of the old habits that I had when I was younger and save my $$ for the parts that I break practicing! I can see a new pipe in the near future too after this weekend! But the stock pipe can take a couple more dents before that time comes around!
You get better too Faded! Good luck...