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Message: [QUOTE="High Lord Gomer, post: 1433662, member: 16469"] My experience has been just the opposite...if/when the valve clearance is gone, once it warms up they will develop more clearance and be easier to start. They are the hardest to start when completely cold. The YZ400 has a fuel screw, not an air screw. Most 2 strokes have an air scren that is to the rear of the slide and it restricts the amount of air through the idle circuit. On the 400 it is a fuel screw at the forward portion of the carb that restricts the fuel flow through the idle circuit. Count how many turns it takes to screw that all the way in. it should be 2-4 turns from lightly seated / screwed all the way in. As I recall, the 400s also had trouble with the accelerator pump delivering too much fuel when the throttle was twisted so you have many things to check. To start I would suggest taking the carb completely apart and making sure that all of the jets and orifices are clean and not gummed up or clogged in any way. While it is off the bike set the float level and check to see how long the accelerator pump squirts fuel. Checking / setting the valve clearance involves removing the valve cover, checking the clearance between the cams and buckets and replacing the shims under the buckets as necessary to get the proper clearance. [/QUOTE]