Jetting

J

jboomer

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Jan 5, 2002

1,420

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• Jan 5, 2002

• #1

I just bought a PC pipe and shorty silencer for my '01 Kx250. I haven't made any jetting changes to it, and as far as I know, it's all stock. It ran a little rich with the stock pipe/silencer. Drooled out the end of the silencer and smoked lightly. Now, I get a trace of smoke at all speeds. I haven't really revved it much. I checked the plug today after riding for about 30 minutes (in the woods) at mid-rpms and lower, very little highs, and 1-3rd gears only. One side of the plug was white and the other side was powdery carbon that could almost be blown off with a puff of air. The bike sounds fine, I suppose. The plug was brand-new (changed yesterday). I don't think it is pinging (never heard pinging though, don't know that I would recognize it if I did). It runs great, much better than with stock pipe, but it better with a 300 dollar mod! Does the jetting seem OK or is it a little too lean? It is cold now (20-40 degrees) and I understand that cold temps cause bikes to run lean. Will it richen up much as it warms outside? I run 93 octane and Golden Spectro at the recommended mix (52:1 with this brand I think). Does everything sound OK? Thanks for any help!

 

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snaggleXR4

Member

Aug 5, 2001

309

0

• Jan 5, 2002

• #2

Hey,
2-stroke experts will give you a better answer, but from you description, it sounds like you are a tad lean. The plug should be a light brown, like Nestle Quick or something. Whiteish means it is to lean. Maybe try adjusting your airscrew, should be on the back side of your carb. Again, 2-strokers will have more details for you. Good luck.

 

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yardpro

Gone Bye-Bye

Oct 15, 2001

529

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• Jan 5, 2002

• #3

call pc support. they will give you baseline jetting recomendations.

 

C

Chief

~SPONSOR~

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Aug 17, 2001

682

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• Jan 5, 2002

• #4

I've never changed to an aftermarket pipe, but as far as the temp changes I can tell you from 80-90 degree weather down to 20-40 degree weather definetely requires richer jetting. I think my main was pretty rich (165) during the warmer weather, but the bike ran smooth so I let it go. During the summer I had the jet needle leaned down one from the middle position and a 48 pilot. Now that it gets below 30 I have gradually gone to a 52 pilot and needle in the middle spot. There is no way my bike would run decent with this jetting in the summer.

I generally try to go as rich as possible until the bike 'craps out' and then go a little leaner from there on the main, needle, and pilot. I read that on DRN and it seems to work great for me. My bike will surge after I run WOT if the pilot is too lean. If you do change any jets, be careful not to crank them down to hard, they are brass and I cracked one with surprisingly little pressure.

I like to see a little smoke out the back. It smokes quite a bit before it warms up. Then it's usually just a light puff. Once in a while it seems to smoke a lot when I stop after a long run, let it idle, and gun it a few times, haven't really given this much concern, I think it might have more to do with the silencer packing that needs replacing, but that's another story, anyway. good luck. Glad you got a nice performance change, must be nice.

Joe Chief

 

M

marcv125

Member

Oct 29, 2001

727

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• Jan 7, 2002

• #5

chef i know this question is asked alot but how do you change needle clip position. I tried before but the springwont come off so i can get to the needle?

 

C

Chief

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Aug 17, 2001

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• Jan 7, 2002

• #6

I don't have a Mikuni Carb so I don't know. Just guessing, I read you got as far as the spring. If you have the top of the carb off with the cable still attached to the slide, compress the spring against the top of the carb by pulling it up the cable, then pinch (don't bend it) the cable with your thumb and index finger to keep the spring tight and the end of the cable exposed. Hold the slide with your other hand and move the tip of the cable first down, then sideways out of the slot. You also might have a circular plastic fitting on the end of the spring. Hopefully they are alike enough for this to help.

When you change the clip position, lay the needle on it's side with the open end of the clip facing down. (I use the top of a steel toolbox) then push down on the needle til the clip pops off. Cover the needle with something like a rag so the clip doesn't go sailing off to parts unknown. Put it back on using the same way except face the opening up and push down on the needle. Lower clip = richer mixture.

If my spring wouldn't pull out at all I would try a shot of wd40. Hope it helps.

Joe Chief

 

S

spanky250

Mod Ban

Dec 10, 2000

1,490

1

• Jan 7, 2002

• #7

Originally posted by yardpro
call pc support. they will give you baseline jetting recomendations.

Click to expand...

Unless you ride side-by-side with the person that came up with those specs, you are just rolling the dice. Jetting depends on temperature, humidity, altitude, engine mods, oil ratio, etc... The variables are too many to use someone elses specs unless you are riding in the same conditions, on an identical bike.

Try this link. It will give you all the info you need to be able to jet your bike correctly: http://ericgorr.com/techarticles/carbtuning.html

 

M

marcv125

Member

Oct 29, 2001

727

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• Jan 7, 2002

• #8

thanks a lot chief 1 more question though.there seems to be some kind of retaining nut that holds the needle in place i guess..how do you get this out..i also have a mikuni

 

B

bigred455

"LET'S JUST RIDE"

LIFETIME SPONSOR

Sep 12, 2000

782

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• Jan 7, 2002

• #9

jbBOOMER you need more time on a new plug it won't begin to show color for atleast an hr.The white you are seeing is the insulator still original color,like i said it takes a while.

 

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yardpro

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Oct 15, 2001

529

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• Jan 7, 2002

• #10

spanky250
you'r5e right. but since the guy doesn't even know how to change the needle position, i thought that pc would be able to give him a starting point if the stock is way off. My 99cr for example came stock with a 190 main. FMF, boyseen and the rags ( oops, I meant mags:p ). all recomended a 175. I started there and fine tuned.

 

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Pit_Monkey

Member

May 19, 2001

253

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• Jan 8, 2002

• #11

hey i have a couple of questions about jetting. this summer when i would ride my bike it would ooze carbon from the powervalve vent hose. i knew that the problem was the jetting however i didnt know what to do to fix this problem. that is where the twist comes in, i pulled the bike out on sunday, the temp. was about 30 degrees and the humidity was like 30% and the biike ran flawlessly. it didnt ooze at all, it had perfect throttle response and didnt smoke at all. so i suspect that the jetting was set up for this temp. what changes should i make in order to set it up for the summer when its 80?

 

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yardpro

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Oct 15, 2001

529

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• Jan 8, 2002

• #12

what your bike oozed is oil mixed with carbon. the reason your bike oozed when air thems were hot and great when cold is because of air density changes. your bike was running too rich in the summer ( too much fuel) the reason it "corrected itself" when it became cold is because cold air is denser. this gives more oxygen ( what your engine really runs off or, fuel is merely used to ignite the air). since you are getting more oxygen per volume of air the bike runs leaner. when it warms back up try to determine where in the throttle position the bike is rich ( 0-1/4 throttle is the pilot, 1/4 to almost wide open is needle position/diameter/taper, and wide open is main jet size) the air scewr is idle and just off idle. you will need to drop the needle ( raise the clip), or go to a smaller jet size ( pilot, main or both, depending on where the bike is rich)
hope that helps.

 

Last edited: Jan 8, 2002

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Pit_Monkey

Member

May 19, 2001

253

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• Jan 8, 2002

• #13

yea that helps a lot thanks

 

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yardpro

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Oct 15, 2001

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• Jan 8, 2002

• #14

see i can be nice.:)

 

C

Chief

~SPONSOR~

Damn Yankees

Aug 17, 2001

682

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• Jan 9, 2002

• #15

marcv125,

My bike has a keihn, not a mikuni, hopefully they are similar. Just find a socket that fits (maybe a 6mm), take the nut off, and the needle should drop into your hand when you turn the slide upside down. Don't go too crazy on leaning the bike out. One position in either direction on the needle makes a big difference in the way my bike runs, the main and pilot jets to a lesser degree, but still very noticeable. If you think you hear it knocking after you've leaned it out, don't run it!!! I seized my bike last year and it really was a sad day. DOH!

Joe Chief

 

M

marcv125

Member

Oct 29, 2001

727

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• Jan 9, 2002

• #16

alright here is my perdicament..i have a 2000 yz125 w/ a fmf fatty/shorty combo and a delta 2 v-force reed block. I changed the jetting to fmf specs w/ the needle in the right position and the main jet changed. When i am riding am i all of a sudden give it full throttle the bike seems to wanna bog for about a second then it screems on. Will changing the clip 1 more leaner cure this? thanks chief..