How to jet your bike

[jzanehope]

Ok now that I understand the jet issue I still have a question. I have an '07 250EX with a HMF full exhaust kit, and K&N filter. I know I need to rejet but the confusion came with the exhaust kit from HMF. They sent me a 125 jet with the kit. Stock on the 250EX is a 95 jet. Oh and all they sent me was a jet, no needle at all. Shouldn't there have been other parts than just a lone jet? Isn't this an extreme jump in jet size for my bike? I also have an "Outer Wearz" pre filter for running with the airbox lid off but the one time I tried it, it bogged too much so I put the lid back on. My elevation is 3,000 to 5,000 feet. Shouldn't I just go up to between a 100 and a 110 jet? Also last sunday I went riding all day with just adjusting the fuel screw and it had plenty of power and super throttle response but the temp gague was reading a consistent 330 degrees on average with the ambient temp about 70. Isn't this too hot? Does that mean it may be running a little lean? I pulled the spark plug to check it after riding and it looked great. mostly black with a gray electrode which would normally mean it was set just right. I really don't wanna keep riding with out rejetting if there is a chance of damage but I'd really like you all to give me your input on this since I suck when it comes to carb work.
Thanks alot

[leasureryan]

it sounds like a reasmonable increase in jet size to me. Rather rich than lean. I would try the 125 with the air box lid off and outerwear on. You have to realize you are moving alot more air now, so you will need alot more fuel for the proper mixture. Try the 125, if the plug is wet, or if it boggs from to much fuel, go buy the next 2 sizes down jets from the dealership. Also, needle size only has to be changed when you are doing MAJOR upgrades. For minor upgrades like this, you will only need bigger main jet, maybe, just maybe go up one size pilot(slow) jet size too, Test and tune bro!, Start rich though.

[97WarriorRider]

hey..where is the air/fuel screw on the 400ex carb?

[Bolinracing]

1) I also need to know, where is the air/fuel screw on a 400ex carb. Also, is it an air screw or is it a fuel screw. This way I know which way to turn it.

2)Same as 1. but for a 450R

3)Backfire(popping) on deceleration means to lean at LJ or pilot jet right? So if I have mile popping when I let off at the end of straights, I should go up one pilot size?

Thanks.

[tcr0148]

yes, you need to change your main jet size to allow more fuel mixture. Also, make sure that you don't have an exhaust leak where the header bolts to the head, because that can cause popping also

[THORrider350]

anyone know what i should do on my 07 yfz 450... i am adding afull alba exhaust... i bought a NCVS needle i am putting on, a fuel screw, and a boysen quickshot cover... and ideas???

[monkeyballs]

Ok well I have a honda 400ex 2002. I have full system yosh pipe and almost no air box lid. (there is like 60 holes in it...) lol. Any who when I jetted it I took out the spark arrestor and I was wondering if it would run better with or with out the spark arrestor?

[Sqwrly]

Okay so I have a 2007 trx450er . It has a stage 2 hotcam, 13:5:1 compression and a full DG exhaust, it also has the airbox removed . And as far as elevation im in florida . I just need some help rejetting . Anyone have any idea on what sizes i should go with? I have a dyno jet kit . A buddy of mine recently rejetted it for me and its still popping when I let off but whenever i just punch the throttle all the way sometimes it bogs like power loss at WOT, I have to roll into it .

I also have popping whenever I let off the gas .

Also what is the stock jet sizes on a 2007 450er ?

[JOHNDOE83]

bogging, backfiring and popping are all signs of being to lean.

backfiring when letting off the throttle poping through the carb are signs of lean pilot jet.

bogging under acceleration is a sign of a lean needle or lean main jet.

the best way to jet for the main jet is to go with large sisize jets till it stutters like a rev limiter at WOT the back it down 5 jet sizes.

the needle rarely needs to be adjusted but may be worth making it slightly richer for piece of mind.

the pilot jet should be increased and the a/f screw turned out until there is none or almost no backfiring.

[tylermiller]

What would you think for a 2004 trx450r with HMF slip on? i was thinking about drilling some holes in the airbox so what kind of jetting would you think?