2010 yz450f starts hard when hot

Jay Henderson

• 261 Answers
• Posted on Dec 07, 2008

SOURCE: motor bike wont rev above idle weth choke on

This to me sounds like you need a carb cleaning. If you have let the bike sit for an extended time the carberators maybe clogged or gummed up. This has to do with the new gas that is out there now. It is cheap and with the introduction of Ethanol alcohol now it is even worse on being stable for long periods of time. I have seen fuel go bad in as little as 3 weeks.. One quick check you can do is open you fuel tank and smell the fuel. IF it smells like varnish it is probably bad. You can drain the tank and add new fuel and that should solve your problem. Keep in mind, that the carbs need to be drained as well to get the old fuel out of there also. Make sure you have a battery charger going when you start crankin that puppy, because you will need lots of extra juice to get that baby to fire up. If it is starting now and runs on choke, that means your idle jets are clogged. Best repair is to remove carbs and clean idle jet. Unless it is fuel injected.
Let me know how that goes and we can proceed from this point. I am a certified mechanic from MMI as well as a HDTV GURU. Smiles. have a good one.

SOURCE: wont accelarate

you didnt say if the bike sat up for a while, if it has you have stopped up carbs the bike will run with the choke on but shut off when the choke is off says no fuel going thru the low speed jets clean them by taking the float bowls off and blowing them out with high pressure air

SOURCE: No power at low revs but works a treat at higher revs.

Hi mate it seems your powervalve is turned up fully, It can give u power on top end ,middle,and bottom end of revs.With it being a 87 a manual valve you will have to take off your exghust off.Now take a look into your engine through your exghust manifold and turn the power valve round ,you will see the hole in which the burnt gases escapre gets bigger or smaller by adjusting this gap you will find the perfect riding style for you (agressave or plesant ) remember to tighten all nuts up ,as you dont want your valve spinning round cus it will shread your piston and rings to death. hope this works
scotty

SOURCE: yzf 250 wont run without the choke

Hi mikelapt
You will have a carby problem. When the choke is one, and different fuel circuit is used. When you turn off the choke, you go back to the idle circuit of the carb is used, when under throttle, main jets kick in. You probably have a blockage in one of these circuits. Strip the carb down, clean with carby cleaner, blow out all air circuits and jets with compressed air, then setup the idle mixture and tick over speed. Always work with fresh fuel, and drain off, discard any fuel older than a couple of months. It goes off, and turns to a gel  like substance that blocks up your carby. Hope this has explained your problem. Happy to talk to you more about it. A FixYa vote is a great reward for for my time taken to explain this to you. Cheers
regards robotek

SOURCE: very hard to start after the engine is hot

I had this problem before. Here a quick glimpse of what could have been the problem:

Fuel is is filled into the carburetor by the float switch. Starting from cold, its just normal that the carburetor is up and ready for a start. As you cruise along, the carburator is filled up with fuel coming from the fuel tank and is regulated by the float switch. Now, if the engine consumes more fuel than the rate of flow by the float switch, then it will drain the carburetor fuel reservoir empty. What could be the cause? You guessed it right... dirty jets or clogged fuel jet on the float switch. Solution: Open up the carb, clean every hole with wire brush. Blow compressed air on the needles and every hole you could see.. Take not of the ball bearings inside make sure there isnt anything loose when blowing with compresssed air.

Assemble the carb back and cruise for 20 minutes.

Other cases: dirty spark plugs, missfiring plugs, or worse case, CDI ..

Let me know if this helps.