My 2000 wr 400 wont start!

I have about 6500 miles on my wr400 sm that i built and for the past 2 months i have had it it would start first kick. It always ran amazing and ran great last night, but this morning it wont start. I pulled the spark plug and it looks great, drained the carb and plulled it off to make sure it is working properly and its getting fuel witch it is, so the only thing left is the valves. this is my first Wr, i have always had RMZ's for racing and the vavles needed shimmed alot but they would still start with some effort. do you guys think its the vavles? and if not give me some other ideas to check.

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I had a similar issue with my 03 WR450F that was sitting in the trailer since October and I was trying to get it going last week. After reinstalling the battery that I put on the battery tender over the winter I tried a couple of kicks rather than using the starter and noticed that the compresson did not seem right to me. I removed the plug and put about a teaspoon of oil down the sparkplug hole, reinstalled everything and within four kicks the bike was running.

After allowing the bike to warm up I checked the compression and everything was normal. It appears that when the bike sits for a while and is not properly stored (I should have oil fogged the motor before putting the bike away for the season), the rings do not seal properly but the teaspoon of oil trick seems to be all that it needs.

The only time my 2000 wr400f would not start was when the plug went south, it fired and ran beautiful, then stopped as I was putting my helmet on, never to fire again until I replaced the plug. Replace the plug and test it again, apparently those plugs run perfect until they don't run at all.

IF you are going to the trouble to take everything off to change the plug you should check the valves at the same time, ony a few more bolts and a bit more time and then you know for sure.

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