needle and main jet tunning

[3leggeddog]

dammit and i have been tossing some ideas around and would like some other input.my bike has a stumble in the mid range under full throttle,then cleans out in the top end.is this caused by a lean main,and can i tune it out with the needle.what exactly is the needles function?i thought it was partial throttle untill the needle is all the way out of the main,but why is my bike cutting out under full throttle then smoothing out?any suggestions would be great,thanx

[Mr. Sandman]

The needle is 0-1/4 throttle, pilot jet 1/4-1/2 throttle and main WOT. Sorry, but no suggestions without riding it and the web diagnosis is too hard.

[TimSr]

The needle is 0-1/4 throttle, pilot jet 1/4-1/2 throttle a

I think you accidentally switched those around.

[3leggeddog]

so i should be able to use the needle to tune out the stumble????well if i lower the clip it will richen it in the 1/4-1/2 throttle area correct

[Mr. Sandman]

Yep, my mistake. Here's a little more detailed info on the jets and their function.

Fuel Jets, Air Jets, and Throttle Positions

Three circuits control the air: the air-screw, the throttle slide, and the air jet. Four circuits control the fuel:
the pilot/slow jet, the spray-bar/needle jet, the jet needle, and the main jet. The different air and fuel circuits affect the carb jetting for the different throttle-opening positions, as follows:
*Closed to 1/8 throttle, air-screw and pilot/slow jet
*1/8 to 1/4 throttle, air-screw, pilot/slow jet, and throttle slide
*1/4 to 1/2 throttle, throttle-slide and jet needle
* full throttle, main jet

[Dammit!]

You might end up wanting to experiment with different needle tapers also. Can't help you much there because I haven't done it myself but the needle taper is supposed to have a signifigant impact on mid range.

[TimSr]

Warm it up, then put in a very clean or shiney new plug, run it up to about 3rd gear, and hold it at half throttle or slightly less for about 30 seconds, pull the clutch in and hit the kill switch, and let it roll to a stop. Before starting it again, pull the plug, and see what it looks like. (Its good to carry your non test plug, to put back it and drive it back to the lighted garage.) If it looks lighter than a good piece of toast, raise the needle. If it looks darker than good piece of toast, lower the needle.

[Wickedfinger]

I had to whip it out Tim ............ Take a look at my chart.

[TimSr]

I had to whip it out Tim ............ Take a look at my chart.


IM BLIND!!!!!!!!!

[Wickedfinger]

... I guess I could mute the colors just a little bit .... The idea was that you could see it from space though.

[3leggeddog]

cool that chart helps alot,and i'll try the half throttle plug check.did you steal the color scheme of that chart from the scheme on tims bike??,lol just kiddin tim,don't hit me with a wheel spacer,thanks guys


for everyone else,tim hates my wheel spacers!!!!

[twgranger]

did you steal the color scheme of that chart from the scheme on tims bike??,LMAO!!! :w00t:

[a-camp]

With a jet removing tool you can change your main on the bike.Couple paper towls and you dont even get gas on your bike. If your main was to big may be the opposite :could be flooding at lower RPMs and ketching up later. I dont get into taper solutions stay with the basics. FMF has a good jet chart that comes with thier pipes Im sure someone on this site can post it.

[TimSr]

cool that chart helps alot,and i'll try the half throttle plug check.did you steal the color scheme of that chart from the scheme on tims bike??,lol just kiddin tim,don't hit me with a wheel spacer,thanks guys


for everyone else,tim hates my wheel spacers!!!!

I like them on YOUR bike! Then I can laugh while Derrick takes pictures of you stuck. I just dont want them on mine.

[Derrick Adams]

[QUOTE=TimSr]Warm it up, then put in a very clean or shiney new plug





This means less than 10 years old!

[3leggeddog]

everybody's a funny guy.if you makes you happy tim,it just tickles the $h!% out of me,glad i can make you laugh

[Dammit!]

Well this was unexpected. Took the R out today to work on the jetting (finally). Turns out the 170 main is way too lean. A WOT plug chop showed the new plug was totally white. I didn't think lean would be a problem after putting around the neighborhood. If anything I was expecting it to be rich and didn't have any larger jets with me so that was a short ride. Just picked up a 175 and 178 so I *should* be ready next time. Pretty sure I can skip 172.

It ran good though with the new carb and rad valve in there. Very smooth power delivery when you want it to be but would still quickly come alive on command. I'm liking it so far. If I don't work tomorrow I'll try again. Would be nice if there was a place closer to home that I could do this...

Also, I noticed zero "air turbulence" issues from having that Uni bolted right up to the carb.

[twgranger]

Well this was unexpected. Took the R out today to work on the jetting (finally). Turns out the 170 main is way too lean. A WOT plug chop showed the new plug was totally white. I didn't think lean would be a problem after putting around the neighborhood. If anything I was expecting it to be rich and didn't have any larger jets with me so that was a short ride. Just picked up a 175 and 178 so I *should* be ready next time. Pretty sure I can skip 172.

It ran good though with the new carb and rad valve in there. Very smooth power delivery when you want it to be but would still quickly come alive on command. I'm liking it so far. If I don't work tomorrow I'll try again. Would be nice if there was a place closer to home that I could do this...

Also, I noticed zero "air turbulence" issues from having that Uni bolted right up to the carb.You should have bought a dial-a-jet like you wanted. ;)

[Dammit!]

I was going to but the dealer talked me out of it! :wondering

[twgranger]

I was going to but the dealer talked me out of it! :wondering
You mean the Stealer? They dont know sh#t!!

[Dammit!]

Was kind of odd that he would talk me out buying something that HE sells though. He didn't really have anything bad to say about it. Just said they're not worth the money. Of course some lucky people find them for 15 bucks on ebay.... :mad:

[x.system]

Ah, you don't need one of those if you know how to jet a carb. I just jetted my trx sunday. I installed the 39mm I normally only use for winter and found it was quite a ways off but this is on a different motor now. I started out with a 175 main and had to go up to a 205 for this 10 degree weather. I jetted this at my house and had a 190 main with a nice brownish plug but once I got out to the track and ran a couple laps found I was running way lean. I jumped up to a 200 and ran a couple laps again. The plug was a little light so I changed out to a 205. I like my motor to run crisp so I rejet every time I ride. Michigan weather changes from day to day so much, rejetting makes a huge difference. Even if you did have a dial a jet you still have to get it really close in order to get any function out of it, right? How far do they say the dial a jet will fluxuate? We were doing 10 lap sessions on the ice and I bet I pulled that plug after every session trying to get it perfect. I probably had about 15 minutes into jetting, including changing jets and making laps but I do this no matter where I ride.

[max]

homboy. y you strugglen. it dont take a rocket scientist. you need to check you muffler bearing. its probably causen it to run rich.
your informative friend
max

[Dammit!]

homboy. y you strugglen. it dont take a rocket scientist. you need to check you muffler bearing. its probably causen it to run rich.
your informative friend
max

:wondering

/head explodes

[x.system]

:w00t: :w00t:

[a-camp]

[QUOTE=Dammit!]Well this was unexpected. Took the R out today to work on the jetting (finally). Turns out the 170 main is way too lean. A WOT plug chop showed the new plug was totally white.


Tell me about your set up ? I run a 148 main so this is fascinating to me .I am ported 1st over about 187 or so Rad Vaulve FMF pipe ,and KNN filter.I have never seen a light plug yet. I ride at sea level over 65F most of the time.

[Dammit!]

MX ported, fmf fatty, 38mm PWK carb, Rad Valve, Uni filter bolted right to the carb, bored (but not sure of the size) and that's about it that would effect the jetting. With the stock carb I was running a 160 main. After reading x.systems post I'm wondering if a 178 is gonna be enough. Elevation is about 1100 feet and very dry. Temp today was probably 72.

[a-camp]

Oh The carb size and the lack of air box explains it . I bet shee Ripssss. Where you ride?

[x.system]

I always jump 5 sizes at a time and then narrow it down from there but I have every jet from 160 to 225 I think. I don't ride every week either, thats why I jump 5 sizes at a time when I have to.

[Dammit!]

Oh The carb size and the lack of air box explains it . I bet shee Ripssss. Where you ride?

She rips pretty good. Just got to get her dialed in.

Only riding I've been doing is local desert places. Went to 11.5 today (near lake pleasant), last time was sycamore creek way out on the east side. Itching to go to the dunes in a big way though. Never been there yet.

[Dammit!]

Finally got pics of the adapter 3leggeddog sent me that goes between the stock filter boot and the carb for easier mounting. I'm not using it yet (still have the Uni clamped right to the carb) but this is what it looks like for those that wanted to see.

I've only ridden once since I got this thing hooked up so I'm going to mess with it the way it is a bit more before I try using this to get the airbox back on. Seems like it would work though.