2007 New valves won't start cold

I have an 2007 crf 450 and put new kibble white valves in and ran good for 40 hours or so and now won't start cold but once warm starts first kick. And it's jetted right, valves are in speck, have no clue what's going on. I'm doing a compression check tomorrow. If anybody can help let me know. :ride:

now i checked compression and its good too

Check your timing. Sometimes the chain can skip a tooth and it starts running really funny. If you pin it and does a wah-wah-wah type thing in the high RPM range, that's another indication of bad timing.

If you don't see that the timing is off, then check the valves again, and "in spec" is only +/- a thousandth, so make sure that's the case.

If neither of those, then IDK!

Ya all of that is good I have no clue. I even tore the head off and checked that the valves are seating right and cleaned the carb thoroughly. I have no clue what could be wrong.

Did you clean the carb thoroughly yet? That fixed this problem for me.

Edit

The tiny passageway the fuel screw goes into was partially clogged on mine.

If it ran fine and the valves haven't moved Id suggest that you've got something in the carb. And as suggested above, its probably in the pilot circuit. Its the easiest to clog or obstruct too.

If it ran fine and the valves haven't moved Id suggest that you've got something in the carb. And as suggested above, its probably in the pilot circuit. Its the easiest to clog or obstruct too.

Cold needs a slightly richer setting then warm so this sounds like the most plausible cause to me as well!

first off a compression test is a waste of time. The cam has a auto decompression system that releases pressure via the exhaust valve. If you want to test the motor do a leak down test.

Check the "HOW TO TIME YOUR CRF" sticky at the top of the forum. Very easy to get a tooth off.

Like said clean the pilot jet but also make sure the hotstart plunger is clean, put a light film of grease on it, then reinstall and make sure you have slack in the lever. If the hot start circuit is open it will creat a lean condition.

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