I bought an 04 yz450f from a friend. It had been sitting for a while so i did a complete service on it (oil, filters, plug, ect.)I also completly cleaned out the carb and jetsand removed old fuel. Took it out and it ran and started great all day. Went to go ride the next day and now it won't start. If i put the choke on and pump the gas a few times it will start for a second and then die. I assumed this was from the acelerator pump injecting the small amount of fuel. If i spray a little bit of starting fluid in it it will run for a few moments and then die. Sounds like a fuel issue so i took apart the carb and cleaned everything again. Still have the same results? The compression seams to be good and all. I am used to 2 strokes so this has me just confused now!!!!