2001 yz426f hard to hot start

My 2001 yz426f runs and rides great for about 5 minutes then starts backfiring/popping then dies.  The only way I can restart it is if I twist the throttle 20 times or so before kicking it. It's like it's running out of fuel. My carb was just cleaned, new fuel, pilot jet,  and a new plug was installed ngk cr8e. any suggestions?? Thanks

Take the gas cap off and test that you can blow air through the hose, to the cap, and out the under side of the cap.  There is a one-way valve in the stock vent hose that can get turned around backward, too.  It's marked.


Another test is to simply loosen the gas cap as soon as the trouble starts.  You might hear or see the air rushing into the tank, and the tank expanding when you do so, or it might just clear the problem up.  Either way, if it doesn't vent the tank the right way, it won't stay running.

The vent line is working properly and I can blow through it without issue. any other suggestions?

From the free end of the hose through the cap? OK.  Next check the fuel flow from the tank.  Should flow at about the rate of about a cup in 8 seconds.  If that seems OK, check the flow past the float needle.  That will be a little slower, but it should be fast enough to fill the carb in just a couple seconds.  If either of these things fails, check the screens on the petcock or the needle seat.

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