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yz250 06 choke wierd

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Hello all, i recently sold my yz250f for this 2 stroke.

i have given up on using the choke, if i use it when dead cold the bike screams so i have to quickly shut the choke off then it idles normally, once its been idleing for about 1minute i can use the choke without it revving to the moon e.g. it acts normally but only after running without the choke for 1min. Bike has been fully rebuilt 30 hours ago and has this problem before rebuild. rebuild include gearbox bearings/gears/crank rebuild/new cyliner/new piston.

i run 40:1 castrol tts.

I realise its prolly the carby but my local dealer writes it off as being not a problem worth worrying about.

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from what i remember my old 07 yz250 did the same thing. Everytime pulled the choke up it revved really high. But I thought it was an air leak and i dont think it was. But i thought jetting could possible help that out.

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my 05 does that when its cold unless I go bigger on the pilot jet.

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might been a touch lean on the pilot circuit. have you tried to turn the air screw in a touch to richen it up?

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Our '06 & '08 do the same thing. Crazy revs on a cold start with choke. It sure turns some heads!

We have learned when starting to keep a finger close to the kill switch, and use that to slow the revs until things settle down.

We've never messed with the jetting. Bikes run awesome all the rest of the time.

I was told before in this forum that it was normal, get used to it. :lol:

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How does the bike idle/low end once warm? Does the idle "zing"? Excessive revs usually mean a lean condition. The choke on a PWK increases air and fuel a set amount. I suspect your low end mixture is lean as my 06 does NOT do this so I would say it is not "normal". My bike was rebuilt only a few hours ago and is mechanically tip top...

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wow thanks for all the replys! in only a few hours, i love this site more all the time.

just as Captdan said, i have my finger close to the choke when kicking it over so it doesnt rev 2 high dead cold, once its warm its fine runs mint, idles for 30sec or so

unless i blip the throttle or turn choke on but the choke acts normal when warm. havnt touched the air screw either.

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oh captdan said "has a finger close to the kill switch" not choke, thatl be a little easier lol its hard to kick and have a finger on the choke at the same time. its almost like if i didnt use the choke at all it would have no weird problems, except the occasional time when it wont start without choke :S

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Both of my YZ250s and both of my KX250s over the years (any bike I've had with a PWK carb.) have idled very high at first with the choke on regardless of jetting and configuration. This seems to be the norm.

I usually just flip the choke on and off for the first minute or so when it's cold out. No problems as of yet :lol:

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Pretty sure the manual says to start the bike and immediately flip off the choke when it starts. That's how I've always done it and I have no issues.

But I'm one of the guys who think a two stroke MX bike should not be set up to idle.

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My 06 does the same thing if the Pilot is lean. If you start playing with the air screw every time you ride, you'll be amazed how much crisper it can run.

I thought mine was jetted perfect until I adjusted it. It's actually pretty sensitive, I think I stay within about 3/8 of a turn from -40 to +40 degrees. If it's colder than the last time you rode, just go in 1/8 or so on the air screw and try it from there :lol:

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its normal for the bike to idle high when choked.

this also helps with knowing your overall PJ jetting if its lean or rich.

if youneed the choke to start the bike becoz it wouldnt otherwise, then you have a lean condition or a perfect size PJ.

if you dont need to open the choke, then yoiu PJ is rich or overly rich.

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i dont often need the choke, only when the bike hasnt been started for a few weeks, otherwise itl start first kick without choke, idle for a few minutes on its own until i need to start blipping the throttle e.g. its warm.

So you think i should play with the air screw? have never touched the jets in this bike, It came with PC works pipe/shorty combo. I have wondered in the past if the jetting is correct but all i did was look at the spark plug colour which was a nice tan brown.

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when i start mine cold with choke revs skyrocket but i quickly shut it off and it idles a touch higher than usual but once warm it idles perfect, like ting ta ting ting, it must be normal on these bikes?

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If your bike will cold start in cold weather without the choke than it IS excessively rich. Most 2 stroke guys get scared to lean the bike out in fear of blowing it up. Then they end up running so rich they just waste a lot of pre-mix and muffler packing...

Dont trust plug reads alone. Pre-mix and fuel additives vary and can change the plug color...

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My 06 did the same thing, I would regulate the engine speed by pressing the kill switch. 2 or 3 times is all it took then would idle normal. Weird, no other smoker I have owned has done this.

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Pretty sure the manual says to start the bike and immediately flip off the choke when it starts. That's how I've always done it and I have no issues..

Yep. Choke on, kick, start, choke off.

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Cold starts with the choke.

I would say with a Keihin PWK carb under the right conditions it is normal for cold starts with the choke to produce a higher idle rpm when the motor initially starts. A cold start would be the first start of the day or when the motor temperature is equal to or lower than the ambient temp. It is also normal for that initial idle rpm at cold start to increase/decrease as the ambient temps change with the seasons. On hot summer days (say @ 80*) my PWK equipped bikes have what I would say is a barely noticeable (if at all) increase in initial idle rpm at cold start. But as we move towards fall and the ambient temp begins to drop, the initial idle rpm during cold start ups with the choke increases. The cooler it gets, the higher the initial idle rpm's climb. Around here it doesn't take long (@ 60*) before cold starts with the choke produce a runaway idle.:lol:

It seems though that shortly after start up, as the motor begins to warm, the idle rpm always heads back down.

I wouldn't recommend adjusting the pilot circuit (pilot jet/air screw) in an attempt to correct this as I think it's a result of the starting circuit, which is only active on your 06' YZ 250 when the choke is pulled up. Most jetting threads talk about changing or cleaning pilot and main jets but the carb has a starter jet too. Unfortunately its pressed into the carb so it can't be removed but an attempt should be made to clean it since it can plug up as easily as the other jets.

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