Jetting Questions

[JPhonda]

hey i have a 2002 400ex and it has a white bro r4 slip on and a moose racing air filter. The guy that i bought it off of never jetted it. I was talking to my friends the other day and they said i shouldnt jett it because they say it only runs good if you runing at the tempature that you jetted it for, and i ride in the winter a bit which its rare it goes over 32F over here and i also ride in the summer where its anywheres from 60-85F. What do you guys think should i just leave it the way it is or should i jett it. If you think i should jet it then do you recommend the dyno jet kit

[2004exrider]

If its still the stock main jet then im gonna say rejet it, its running lean especially since its cold right now. The stock main jet is a keihin 148 so i'd go to a dealer and pick up a few different KEIHIN jets. Try a 155, 160, and a 165, you shouldnt need to go any higher. See which one runs better for you and use that one. come summer time you'll only have to go down a main jet size just because it will run a little richer. I'd go that way because youll have only spent about $10 compared to the jet kit which is over $50. Any other questions about jetting feel free to ask. I or others will chime in to lend a hand:)

Jimmy

[JPhonda]

I was told by some friend that i shouldnt jet it at all because its just to much of a hassle and the fourwheeler well be fine the way it is. Is this true or if i dont jet it well i cause harm to my engine?

[flauge]

ive got stock jetting on mine withan e series and powerfilter and it runs fine. also had stock jetting on my old 300ex back in the day also. it should'nt hurt anything but u wont get the full potentional out of the extra airflow you have goin in and out...

[hotrodbelair]

did you ever check the plug to see if you were running lean.

[JPhonda]

no ive never checked the plug i just got the fourwheeler so i really didnt do anything with it yet. This spring is when iam going to change the oil and plug so. Also when its running lean whats the plug look like

[hotrodbelair]

if the jetting is right it should be a brown plug. if its running lean the plug would be white or grey color.

[2004exrider]

rejet it, its not that hard. Think of it this way, take 10 minutes out of your life and put in a main jet. Or run it like that for a while (if its running really lean) and replace the piston or exhaust valves, id rather do it the right way.

Jimmy

[04'400ex'er]

Originally posted by flauge
ive got stock jetting on mine withan e series and powerfilter and it runs fine. also had stock jetting on my old 300ex back in the day also. it should'nt hurt anything but u wont get the full potentional out of the extra airflow you have goin in and out... You are ignorant. If you dont rejet the bike, you will run it lean and take a STRONG chance of burning a hole right in the top of your piston.

To the guy who started this thread...
The dynojet kit is an easy jet kit to use. If you go with kehin jets, put in a 42 pilot, move the needle clip one spot, and start at a 155 main. the main is the jet you will have to play with, the other settings I told you will be spot on. Just keep putting a larger main in until you get a bog, then back off a size and go! The pilot and needle require you to remove the carb but the main jet only requires you to remove the plug at the bottom of the carb and screw the jet out wit a 6mm socket. its a 5 min job. hope this helps.

[IanCFitz]

Originally posted by JPhonda
I was told by some friend that i shouldnt jet it at all because its just to much of a hassle and the fourwheeler well be fine the way it is. Is this true or if i dont jet it well i cause harm to my engine?

Nothing pesonal but those guys are morons.

The first time you take your carb out it might take 20-30 minutes, once you have done it a few times you can have it out in 5-10.

04'400ex'er pretty well hit the nail on the head.

42 pilot
155-165 main

hell, take the choke out if ya want as well.

[tooanxiousii]

With you mods a 165 will work great...

[flauge]

Originally posted by 04'400ex'er
You are ignorant. If you dont rejet the bike, you will run it lean and take a STRONG chance of burning a hole right in the top of your piston.

To the guy who started this thread...
The dynojet kit is an easy jet kit to use. If you go with kehin jets, put in a 42 pilot, move the needle clip one spot, and start at a 155 main. the main is the jet you will have to play with, the other settings I told you will be spot on. Just keep putting a larger main in until you get a bog, then back off a size and go! The pilot and needle require you to remove the carb but the main jet only requires you to remove the plug at the bottom of the carb and screw the jet out wit a 6mm socket. its a 5 min job. hope this helps. first off,dont be calling me ignorant just because you have a different opinion. second, i ran my 300ex like that for over two years like that with no probs, i did finally rejet tho. im not saying that its okay to run lean, but with just a slip on and filter i dont think you haveto worry about burning a whole in your piston. it would help to rejet.

[hauck400ex]

customer brought a bike he hadnt jetted in... its been run for 6 months, probably 100 hrs... the casting on the cylinder went bad from running lean... he had to spend about $600 to fix it

rejet it

[JPhonda]

ok now say if i put in a 165 main jett and its perfect for the summer. But when it comes time for late fall and winter i am going to have to change my jetting again right. Also what are all or your opinions on dail-a-jet. I have been researching it and it seems really but its just the price that is stopping me from buying it. I want to know what you guys think of it, the people that had experience with it or personaly know someone that has used one.

[hauck400ex]

just check your plug every few weeks... if the plug looks good, you will be fine... i run year round with no jetting issues and all i have to do is adjust my fuel screw a little bit

[tooanxiousii]

Like I said put a 165 and if you want to make it run a little fat put a 170 main in... A little fat won't hurt anything you will run a little cooler