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How to determine if jetting settings are correct

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Hi folks,

Well I wanted to report an inital success after doing the following mods this weekend:

cut grey wire

YZ throttle stop

#168 main jet

#48 pilot

#100 pilot air

OBELN clip position #4

1 turn out

@<1000 ft

How do you know of you need to adjust needle position, fuel screw or anything else?

The bike started better and needed less choke. It idled a little better and pushed in choke sooner. Obviously the bike pulled much stronger and smoother from stock settings, it wheelied easier in both 1st and 2nd.

Where do I go from here and what should I look for. I plan on getting a Vortip as I need to keep sound down and open the airbox when I get it.

Thanks a ton.

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you start a thread for everything don't you! well at least you get everyone's attention.

first of all you've got to decide if you're in this to;

get a setting that works and leave it.

get other settings and try them, thereby learning for yourself.

willing to experiment.

it's no good either doing five mods at once like some people.

you're going to have to spend some DOSH as well. although you lot sound as though you meet every weekend, so how about "borrowing" some jets etc to try?

looking at your settings, it looks as though you should be running the 42PJ and the corresponding PAJ which is around #85/#75. how about the PAS that many have got.

drop the needle 1 clip at a time and the bike will rev sharper/quicker. mine yesterday revved beautifully and then popped on the decel. it did it at the moment i closed the throttle and not "on the corner" so i know that the needle is almost perfect but could go up 1/2 a clip perhaps.

your needle may come down 1, 1.5 or even 2 clips.

you really must try my latest experiment that was a HUGE success and that is to put on tall gearing at say 15T x 50T and then try to rev the bike out. then fit the 160MAJ. big difference.

it's up to you pooley. but whatever you do don't keep talking about it!


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Thanks Taffy,

I am trying to get a good all around jetting for trail and woods riding and then generally leave it alone. I found my current setup from JD for another rider who is also at the same elevation (<1000ft). I like to tinker so changing settings is not a problem, its the test rides that are hard to come by.

I was looking for a method or phyical & audible signs that the bike may or may not be jetted correctly. I remember from my street bike that a little popping on decel is ok as long as it is not excessive. I also used to adjust the fuel screw using a tachometer to achieve the highest RPM for the current carb setup.

Having a smooth running bike that does not bog off of idle, die at full throttle or foul plugs on a weekly basis is the main focus. But above all I have to abide by the restrictions for off road use in Michigan: under 94dB with a spark arrestor.

I am not as lucky as the west coast folks who can ride just about any day of the year with tons of other folks. My rides are severely limited in time and frequency. The closest trail is about 3 hours away and haven't yet met any MXers nearby to go ride with. The club rides are over for the year so until March, I'm on my own.

Thanks for the help.

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Your right next to my settings at 1000ft. I went riding yesterday and it was 60 degrees out. Worked great in AA type trails and grasstrack. For some reason my bike likes to be a little richer than others. When it gets colder I just turn the fuel screw. I'm in PA so its the same type of riding.



ELN #5


Fuel Screw 1 turn

Uni Air Filter

2000 WR400

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all the blokes with '02's have got the lowest jetting on this website and you go the other way!

the ratio of 48PJ and #100PAJ is ok so i think you'll run fine.

what to look for? phew!!!!

well look, why don't you go to jetting Q's and i describe every symptom. ok, ok sometimes it's heavy reading, but, you know, you gotta stick at it. or if it were me i'd print it off (50 pages unfortunately) and read it elsewhere.

that's what i do with other technical stuff.


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