Question about 2004 kawasaki KX 250 F

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I have a 2008 KX450F. Starts on 1st kick when cold but really hard to start when hot. Also have trouble with the idle, it is idling very fast but will eventually slow down to normal idle if i let it sit about 10 to 20 seconds but will sometimes stall. Now I had it overheat on the last ride but that could have been from riding it very slow in very hot weather with a broken clutch lever. Not sure where to start. Thanks.

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There is no reason for the idle to take 10-15 seconds to slow to normal. perhaps you have a vacume leak. check all your seal and gaskets between the engine and the carb.also when it is running spray gummout spray or equivilent around the gasket edges between the engine and the carb, if the idle increases when you spray then you have a vacume leak. (intake leak). It may be that this is causing it to be hard to start when it is hot.(not getting enough fuel)

Posted on Nov 03, 2010


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I have a 1986 GMC 1500 with a 5.0 and stock rochester carb. The truck will start but you must keep gassing it as it won't idle. It kicks off every time. Any suggestions on how to fix this cold natured

fast idle speed screw, works off the fast idle cam which the choke adjustment sets, it works together by linkages. This is the raised idle speed setting you need to keep a cold engine running. First you set the idle speed by the idle speed screw with engine at normal operating temperature. Then you set the linkage up so the cam is on a raised step, throttle will be held on that raised step. then you can turn the idle speed screw to get idle at about 1500-1800 rpm. Now when you start engine cold, choke will set the fast idle cam on that raised step- when engine starts and runs it should be running at your fast idle setting. That's how it supposed to work, you just have to get everything adjusted right. I hate carburetors, they never stay adjusted right. Considering their complexity and small mechanical parts, no wonder.

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My 1994 samurai idles really high when I first crank it, but later slow down. is there anyting I can do to ?

From a cold start my sami idles really fast, but as I drive it and the engine warms up it will idle correctly. Is there a way to make it idle slower from a cold start?
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I just got my bike a couple days ago and it'll crank but it's so hard how do you use the decompression lever? Would I need a spark plug cuz it should fire rite up.

Standard starting procedure for YZ400/426/450 is as follows: Push the engine around using the kick starter until you hit the compression stroke. The kick starter will get impossibly hard to push at this point. Now pull in the decomp lever and push the kick starter down a fraction, and I mean a FRACTION. This is where most people go wrong, they push it down too far with the decomp lever pulled in. Now give it a full kick without throttle and it should start.

The above should work fine for a motor that's already warm and was NOT stalled. If the motor stalls it will usually need the hot start button opened as well to let extra air in and bleed out the fuel that usually gets stuck in the motor when it stalls.

For cold starts, you will need to put the choke on, and if it's really cold you might need to prime the engine with a twist of throttle to get the accelerator pump to shoot some fuel in before you start.

As a general rule, NEVER twist the throttle while kicking when you are actually attempting to start the bike, it won't help at all. Also, having your idle screw adjusted correctly makes all of this a lot more easier. Standard setting is usually 1.5 turns out but it should be set to give the smoothest idle you can get using the minimum number of turns out from all the way in. If you have to wind your screw right out to get a good idle you need a bigger pilot jet. Conversely if you have to wind it most of the way in (less than 1 turn) you need a smaller pilot jet. I'm not sure about the 450 but my YZ426 came standard with a 42 pilot jet and changing to a 45 made it idle and start MUCH better. Incidentally the WR model uses a 48.

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1 Answer

89 dodge shadow. hard start. normal idle cold, fast idle warm. sometimes it wont start until i hear fuel pump activate.

The car may be hard to start because it may need a normal tune-up. If the spark plugs are pretty used, they will slowly stop burning as much fuel because the spark slowly gets lesser and lesser. On a cold day the fuel is harder to ignite with a small amount of spark.
Normal idle when its cold means that your cars idle is probably too high. If you lower the idle, the choke on a cold day will keep the idle a little higher until the motor warms and then it will kick back off. If the idle is too high, it will run very rich, smothering itself with fuel, and causing the idle to stay low. When the car warms, its creating better spark when its warm, and with the idle being too high its running at a fast idle.
The car wont start sometimes can be the cause of a few things. If the ground is bad on the fuel pump, it wont make a good connection sometimes for when you turn the key on, the fuel pump dont pump the fuel to the engine. Another one can be that your accessory switch can be loose going to the fuel pump. I think its your ground though. Good luck! Hope this helps.
Have a nice day. -Steve

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My 1993 crown vic has trouble idleing properly when first started in the morning, either in the winter or the summer. Also if i try to take off real quick after the first start it laggs and runs really...

You may want to check the Vacuum lines if there are leaks. Check also Fast Idle Thermo Valve, which controls the idling at cold starts. If you have a carb, check the idle up valve.

Jun 03, 2009 | 1993 Ford Crown Victoria

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Carby runs good cold then terriable

Hey nake sure your timing is correct or also that ur glow plugs are still holding on strong there is also a few other problems it could be like ur fuel injecters cud be blocked or your injector pump may be leaking or sucking air!!! best of luck hope it help alittle!!


Mar 04, 2009 | 1989 Mitsubishi Sigma

1 Answer

Idle fluctuates

Its could be a few things. Most likely cause is you IAC (Idle air control valve) If this valve gets clogged up with carbon it will cause a idle surge on cold starts like you are describing.

Next your FITV (fast idle thermal valve). When the hot wax inside of this valve starts to wear it will cause a idle surge on cold starts.

Dec 13, 2008 | 1997 Acura CL

1 Answer


You need to change the thermostat, it must be stuck open and the computer thinks the engine is always cold, hence the fast idle and smoke.

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