My cbr starts great when cold, and goes great too. But after a short ride it just dont want to start!
Anyone got any ideas?

 

How old is your battery. Are the Cables tight on the battery? Are the a little lose when they warm up?

 

I tryed a new battery and it still did the same, cables are tight.

 

When you have been for a ride, take the plugs out (whilst hot) and check the gap as sometimes they can expand and when you tryto restart, it the spark is not as intensive as it should be. As for the slow starting, could be battery, or bad earth or down to the starting problem your having. Try the plugs first and then see what happens. Good luck

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Just left it for half an hour, its started on the button! what could it be?

 

It could be a short or open overamping the wiring while the key is on. This will cause the cables to heat up and conduct less electricity. I've had this happen on my old Interceptor (electric cooling fan was drawing to high amperage)and a pickup I owned (starter cables to close to exhaust). A real pain to trace. You have to disconnect all normal power draws like the headlights and then check for current draw. Good news is you can check while the bike is cold.

 

Sometimes when the valves are to tight in an engine it will start when cold. When the engine warms up it will run great as the momentum of the valve will seat it. When it is warm the clearance may be to tight to get a good seal for starting. As the engine cools off the valve contracts and closes for starting. I incountered this with a few older cars with manual adjustment valve clearance. If it were me the first thing I would check is the valve clearance.

 

How do you know it isn't fuel starved? Try replacing the vacuum line to the petcock and the main fuel line. No need spend a fortune on OEM parts. You can get bulk 3/8" fuel line and vacuum line at the autoparts store.

 

It also could be the dreaded starter clutch + alternator dampener combo

 

All I know for sure is that when that happens, it is either fuel, spark, or mechanical.