racing cold idle HELP!!!

[elcamino12sec]

Hello all, Im new to the form and this is my first post. I have read allot of good questions and some fantastic answers. My question is for my 1994 kx250. First I will tell the problem: When I start it cold, (begining of my day riding) the engine runs an extreamly high rpm for about 25-35 seconds until it warms up, it does not do this the rest of the day. The next day it will do the same thing. I know it is jetted wrong and Im going to work on that this weekend. I have had quite a few dirt bikes but none have had this problem. the bike will do the same thing when I turn off the gas and run the carb dry. It runs so high it sounds like it may blow up, Both starting and running the carb dry. My girlfriends yz85 will just idle until it dies when I run it dry like all my other bikes have done. It does not idle very well and fouls spark plugs but Im not quite sure thats the main problem with the VERY high rpm sarting problem. Now about the bike, I recently purchased it used with a fresh top end ( I saw the parts that came out of it) it has a boyseen rad valve and pro circuit pipe and silencer, mild port work to the clyinder and head. After the bike warms up it runs strong from idle and pulls strong all the way to the top end very smooth and hard, it has allot of power. If I ride hard it will not foul a plug all day, but when riding with my girlfriend on trails for an hour in first gear it will. My main concern is the problem of the extreem high rpm when I first start it, I dont want to have a cold seizure. Thanks in advance!

 

[Morvo]

Is it me or do all KX's have a tendancy to **** up all of the time? My 1995 KX has had problems since day one :( Definately sounds like a fueling issue though mate, what it is exactly I am not sure. Do you use the choke when you first start it?

 

[biglou]

Jetted way lean? Crank seal maybe? If so, you'll want to get that fixed before it takes you along for a ride you'd rather not be on!

 

[njrealtor55]

do not turn off the gas and let it run dry. you can sieze the engine this way. your engine is basically "glow plugging" or "running away" in both scenerios.

i think your bike is revving real high because when it starts it has no gas - you ran it out of gas before you shut it off. try leaving the gas turned on when you kill the engine. then after
the bike is off, turn the fuel valve to off. then turn it back on when you go to start the bike the next day. i bet your problem will be solved..

try closing your air screw 1/2 a turn or more from where it is now and see what happens when you start it.

if the air screw dosen't solve the start up issue, check the float hight. if the float hight is ok, try lowering the needle 1 or 2 positions. and lastly, get a richer pilot jet if the needle clip dosen't work. ideally, the richer (larger) pilot jet swap would solve everything.

just don't run the bike out of gas anymore. it is not good for any 2 stroke to run out of gas - the gas lubricates the engine.

 

[thing2_and_thing1]

I agree with njrealtor55. I have a 2000 kx250 and I had the same problem with fouling plugs. You can read "2000 KX250 fouling plugs" on this forum and see the advise I got. I ended up moving the needle clip to position 2 and my bike ran fine with no plug fouling. The KX250 is a great bike that has lots of power but they all seem to come stock running fat.

By the way, I think you have to ride all 2 strokes MX bikes kinda hard. Putting around will foul the plugs no matter what you do. I bought the kx100 to ride around with the slower people. Perhaps you just need another bike :nod: You can never have too many

 

[nickyd]

I.

By the way, I think you have to ride all 2 strokes MX bikes kinda hard. Putting around will foul the plugs no matter what you do.

proper jetting will allow you to put around - look at what woods riders have to do...

 

[thing2_and_thing1]

If you jet the bike for putting around, will that make the bike too lean if you dicide to run it hard? Would changing the pilot only to keep the fuel for the big end make the bike surge badly?

 

[Morvo]

So what kind of jetting would you reccomend for me? I run my KX250 in a smallish field (90 metres X 30 metres) half the field is on a steep slope. The track kinda looks like the pic in this link http://i3.photobucket.com/albums/y79/Morvo/track.jpg

We barely get out of third and the bike rarely tops out, more of a mid range track. At the moment we're running the carb on the jetting information provided by FMF as the bike has an FMF Fatty front pipe and a powercore II rear, so it's got a 160 main, 45 pilot, needle in the 3rd position and the air screw out by 1.5 turns. The temperature is usually around 10-15 celcius in the winter and 15-25 celcius summer and very close to sea level as I live on an island.

Cheers!

Dan

 

[njrealtor55]

fmf reccomends 50/50 mix of race gas with thier jetting reccomendations. using race gas will let you lean out the main jet.

If you look at the tables they publish - you can see a trend of 3 sizes lower on the main and 3 larger on the pilot. They post overall jetting numbers(combined pilot and main) that are very close to stock. you will need a main jet that is larger than fmf reccomends if you plan on using 92 octane.

personally, i'd get a larger rear sprocket so you can rev the bike more. i have a 13/53 for the mx track i ride and i'm in 3rd/4th all the time. slow top speed, but coming out of a turn and into a tabletop is no problem now.

telling you what jetting to run won't be right. how does your bike run now? at 1.5 turns out does it have a crisp low end? does it surge when it is decellerating? how is the overall plug color after riding around normally for 5min (not lugging or over reving the engine)?

without more info - anyone telling you what jets to run is just blowing smoke up your (you know what).

 

[elcamino12sec]

Does any one have any recomendations going from stock jetting when one has a boyseen rad valve and procircuit pipe and silencer? Does one tend to go leaner or richer? Just want to know where to start, thanks in advance.