interesting jetting question

[Juggalo]

ok so my friend (crazy casey on here) finally got his new quad today. its a 2002 400ex. its got a e-series full exhaust, K&N filter, and running with no lid. the guy when he dropped it off complained he could never seem to get it jetted right. i asked what jet he was running and he says 165!! i figure wow way to rich right? i mean i am only running a 158 in mine and i have exhaust, filter, no lid, no choke, and a stage 2 cam. so i figure i'll just let casey use the 160 main i had layin around. but when i pulled the plug it was WHITE! i mean damn white, like it was runnin way lean. so after that i was afraid to put in the 160. anybody have any suggestions??

[JOEX]

I'm definatly no expert here but from what I understand it there are many variables involved with plug checking, Mainly with the cleaner fuel that is used nowadays.

This is a copy of part of a thread that I saved a short while ago....


Mickey Dunlap...
With all the different kinds of fuel we see (including unleaded) there is no way to get the right color.The way I read a plug is to ride for 10-15 min. to get it up to temp.Run down the road wide open in the top gear and hold it there for 5-10 sec. then kill the motor, pulling in the clucth and come to a stop. Pull the plug and look at the ground strap,you want to see a carbon line in the middle of the 90*bend. If the line is closer to the tip of the strap its to rich. If it is down around the 90* bend towards the plug threads its to lean.This works on 2 and 4 strokes.It does not matter what color the plug is just make sure you use a used plug that has carbon on it.




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Reading Mr. plug can be Voodoo at best with today's lean fuel. Try this test, I have used it when reading plugs made me crazy.


The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.
If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.
If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one.


__________________
White_Knuckles

[hondafox440]

I always use a new plug to test the main.

Heres a good jetting guide written by spanks at dirtbike.com..



The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

Start with the pilot circuit. Warm the bike completely, and shut it off. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. If you end up less than 1 turn from closed, you need a larger pilot jet. If you are more than 2.5 turns from closed, you need a smaller pilot jet.

Once you have determined the correct pilot jet size, and tuned the air screw for the fastest idle, set the idle back down, and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open.

You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity.

Now, the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time unti the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly.

Last is the main jet. This is located inside the float bowl, and affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

[Juggalo]

wow! soem really great info so far! anybody else? so do you guys think i should lean it out or what? i'm gonna do the top it out method and pull the plug right there on the trails and see how she looks.

[AtvMxRider]

Make sure you start with a new plug.

[DEAL]

What kind of jets are they?
a 165 dyno jet is equal to a much smaller jet.
I'm running a 165 in my quad right now. But if I were to buy a regular jet it would be 150 something in that area.
Sometimes the fuel gives you a false reading also.

[carlj75]

Yup, it's probably a dynojet.

[Juggalo]

hmm well maybe i will tear into the carb tommarow and take a look at the jet since we have to tear into the quad anyways. the kid who sold it tore the whole quad down to get it PC'd. when he put it back together he did a real sloppy job. all the electrical wires are ran all goofy, brake lines aren't right, the linkage arms for the rear suspension are switched (!!) as in backwards and a lot of other stuff. might as well get into the carb and make sure everything is hunkey dorey while we're at it.

[cals400ex]

dynojet jets are a different size than keihin. for example, a 148 dynojet is about a 150 keihin. so, there is only one size difference between the two. i would not necessarily look at the plug. i get two totally different readings with two different types of fuel. with the shell fuel, it looks as if the bike is running really lean. i am running a pipe with no airbox lid and i had a 155 keihin jet in. i went up to a 162 and the plug looked the exact same after i did my full throttle plug chop with both jets in. it has to be additives in the fuel. with the shell, the insulator stays all white and the 90 degree bend on the plug will just be a light yellow. after jetting numerous times, i found that the bike runs best with a 160 keihin in. this sounded really big to me but i have a complete sparks x-6, no choke, uni filter, and no airbox lid. a 162 seems to dog out a little bit and the 165 made it run as slow as crap. jetting takes a while. i have rejetted my bike so many times i am sick of it. i have a keihin 150, 152, 155, 158, 160, 162, and a 165. i just jet, then race my friend on his 400ex and keep jetting until i have the correct one in. on that bike, i would say a 158 or 160 keihin should be close with complete exhaust, no lid, and k & n filter. i am assuming that it has the pro-meg headers. good luck

[Juggalo]

allright so i will throw the 160 in there, and yes its the pro meg. do you think i am running too lean with my cam? i have a 158 and it seems to be ok but it bogs sometimes when you crack the throttle from lower rpms i thought maybe it was just a characteristic of the cam and i was also gonna try to move my needle up another clip and see if that helped but if you think i need more maybe i will put the 160 in mine and give him my 158