just got a rmz250. some jetting questions

hi, just got a rmz250. havent ridden it yet. the jetting was out when i bought it. it would start 3rd kick would idle and run fine but after that when u try it a big rev theres like a flat spot. its not bogging, just a flat spot. the muffler core was snapped in half so i think that might of been part of the problem.

since then i have put a full dr-d exhaust system on. i started it but didnt rev it because it was late at night.

i was told to go 1 size down from the stock main jet ? whats the stock size ?

im in victoria, australia. have no idea on my elevation level.

the reason the jetting was out is because he didnt have the tool to adjust it.



Hey TopGun,

If your bike is an rmz 05 it comes with 178 main and 40 pilot, Most riders stay with the 178 Main But change your Pilot to a 42 and turn the screw out anywheres from 2 to 2 1/2 out, of course it will depend on your temp and air all that other good stuff.

whats the pilot ?

at the moment, the bike has a 160 main jet. i rang up the guy who i bought the exhaust off. he was running a 170 main jet with 1 1/4 turns out on the mixture screw ?

1 1/4 seems a bit strange. should i just put in the 170 and then just play around with the mixture ?

160? :) ...my buddies got two kxf's and both got 182 or one step bigger main jets and both are on the lean side...It's below zero here now...but anyways...wouldn't the bike run very hot with a 160?..or eaven a 170?

I'm really no expert...but that cant be right..unless its really hot/high altitude... :)

saw you were in Australia...summer overe there right now eh? :) forgot!

but still, people are having troubble with overheting, and with that small mainjets I'm not suprised!

If you put a full system on the bike that will make it run leaner, therefore if you change your jetting you should go to a bigger jet size than what it previously had. I can't give you a magic number though because there are tons of factors. Put a new spark plug in it, run the bike, then pull the plug out and look at it, it should be tan. If it's black you need to have a smaller jet, if it's white you need a bigger jet.

adjust from there.

yeh, im turning it into a kx250f. got all the plastics, just waiting for my custom graphics to come.

the jetting was all ****ing wierd in it.

it had a 160 main jet. 178 is stock.

a 42 pilot. stock was 60 i think.

anyway, i put in a 178 main jet which is stock. i put in a 65 pilot jet, left the clip at the stock position. 3 from the top.

the bike wont start. it fired once but stalled. i think i know what the problem could be. when i was putting the carby back on the throttle cables got stuck on something and i didnt see it so it could have been holding it open and probbably flooded it. ill try again tomorrow, putting a new spark plug in it too.

The stock pilot should be 40. Most riders here went to 42 and bike idles perfect.



im going to put a new plug in and drop it back to 42 and leave the 178 jet in it and see how it goes.

I had a hard time starting it once.would not even fire , i could smell gas,I found the idle screw was turned down too much.

ok i can get it going now ive replaced the jets. i put in the 42 pilot and a 170 main jet.

its a bit hard to start and when it does it runs just about perfect with the choke on but when i let it off it backfires and shit. i got it at 2 1/2 turns out.

this is the jetting that other people with rmz's in this area are using.

I would go with a 178 main jet first before you run it anymore and see where your at from their. A good rule of thumb is that you would rather be rich than lean because when your lean you overheat stuff and that's when stuff breaks. If its rich the most you'll do is foul a plug. If its running fine with your choke on that means it is running lean.

When you do this don't use a new plug:

I tell you what, run your bike in a wide open area between 3/4 and full throttle (try to hit full throttle as much as you can) in 3rd and 4th gear for a few minutes and then when your at full throttle, pull in your clutch and hit your engine shut-off switch. Take out the spark plug and check the color of the little ceramic piece. If it's WHITE or GREY your main jet is too lean. If its BLACK, its too rich. You want the color to be a TAN. The 3 things that affect your jetting are TEMPERATURE, HUMIDITY and ALTITUDE.

First of all my '05 runs SUPER!

But after reading this forum my head is swimming from advice.

So, to get my bike to run even "BETTER"....................

I just got my '05 a JD kit and would like your confirmation on the jetting I'm going to use.

The backfire screen is removed, I'll be riding in 65-85 temps, 50-90% humidity at sea level and a little above.

My plan for jetting with your kit is:

Fuel screw turned out to 2.5 (it's a Zip-Ty)

Pilot 42

Red needle 5th clip

Main 178

Ya think I should go up even more on the main?

Sincere thanks, Joe

BTW, I'm sorry to cross-post this from the jetting forum but I haven't gotten a responce in two weeks.

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