After trail riding, I parked my 05 CRF 450 R and was letting it sit there running to run the rest of the gas out of the carb and it started making a strange whining sound. I immediately turned it off and think is was overheating, but I don't know what that darn noise was. It did spit a little coolant out the overflow tube, and a buddie said it sounded like maybe the impeller was making the sound, but I just dont know.

did u try to disconect the cut off switch to see if it is doing the same . and if u keep the starting button in does the starter keep running along

Mine would run for about 15 minutes and die. I pulled the carb off and thoroughly cleaned it. Inside the float bowl there is a plastic device held on by two phillips headed screws. Under this device are two tiny tubes with small holes in the side of them. Make sure these are clean. I used carb cleaner in a spray can and a tip cleaner. Make sure to wear eye protection if you use spray cleaner. I reinstalled the carb and, so far, it is working fine.

Try a small shot (about a 2 second spray) of starting fluid in the air intake then cranking....
WARNING- DO NOT TRY AND KEEP IT RUNNING BY USING THE STARTING FLUID! It can damage your engine.

If your bike fires and runs for a bit, the most likely problem is your gas has gone "sour". You need to drain all the old gas out and properly dispose of it.

Over time, gas will cause a varnish buildup in your carb if it sits too long. You can try adding some carb cleaner to fresh gas, but the results will not be immediate. You may have to have the carb rebuilt.

When you store anything gas powered, there is an additive called Sta-bil that will act as a gasoline preservative for about a year.

Check your plug. If it is the wrong gap or wrong style it could be too hot of a plug. for your bike the plug that should be in there is a NGK IFR8H-11 they should cost $12.30. It's expensive but cheaper than an engine rebuild.

Also it could be running lean, check to make sure the fuel filter is not clogged, or that the gas is stale. If the bike has been sitting for longer than three (3) weeks then you need to clean your Carburetors. It is about $100 per carb with most shops in the US, pricy but if you don't know what you are doing you can spend a lot more doing it yourself.

Make sure you keep the oil filter clean and lubed properly, dirt destroys engines fast.

Check your pilot jet is not blocked or try adjusting your idle screw for the idle issue and it sounds like its runing lean which can also make it idle low and rough and will cause it to pop and backfire. Dont think it has anything to do with your hot start cable that will make it run it run better if its running rich but your is doing the opposite

1. First thing is when was the last time you had your valves adjusted
2. On cold start up twist about 15 times on your throttle, as you do that the accelerator pump in carb will shot gas in cylinder, I have a 2003 yx426 & 2005 yz450 have to do to both of them when cold out to get started

CHeck if there is any problem with the conetion beteween the carburator and the head

Make sure that you turn your fuel to the off position when you leave your bike sitting for more than a day. Gas will sometimes leave the tank, and pass through your carb, and into your cylinder. It will then bypass your rings and seep into your oil. Dosen't happen overnight, but after about a week i becomes common if your float is sticking. Good Luck.22

I have a crf 250 R and i have learned multiple things about these bikes like if you leave it running and not riding it for about ten min. it will over heat. they love race gas 113 octane,and alot more. but your prob sounds strange. i know if you hold the hot start while its runing it pops that could be a problem. or it could be you are not cleaning the bike out i would need to know more about this to give a definate answer but try going over the bike. Look at key parts like the
carb
air cleaner
fuel line
any thing that is nesessary for the bike to run.

Hi jjb
To give you all you need to do change the plug, and swervide the bike, you can download a service manual for free from here. If the the bike has been sitting for a year, to look after the engine BEFORE you start it, you should do a few other things also. A quick list 

1. The engine oil will need to be changed, 
2. clean and check your air filter
3. Drain any stale fuel from the tank and carb, refresh it, prime the carb
   
4. Remove the plug, and put a dribble of 2 stroke oil into the chamber
5. Crank the engine over a few times with the plug out.
6. Fit the new plug
7. Start it up, it may smoke a little initially, but this is ok. 

 Before you go for a ride, good idea to go through the manual and do all the service requirements. Thanks for using FixYa. 
regards robotek