YZ450F starting in cold weather

My Son's 03 yz450f pops and backfires a little when we try to start it during the cold weather. Sometimes it will not start unless you push or pull it to start and it pops and back fires then too. I think it might be the carb, but not sure. After it does crank, it starts with one kick. I also notice that when you give it some gas it spits and sputters like it is missing. Does any body have any ideals?

my bike is inside the house, but my quad do the same.

i think its just runing lean, the fuel mix need to be richer when its -10.

Changing the base jetting won't affect starting that much. If you want to increase the size of your starter jet, that may help, but you'll want to change it back when it warms up.

When starting cold, the engine needs extra fuel to over come the effect the cold metals have on preventing fuel vaporization. Prime the engine by cranking the throttle 2-4 times, and also try it with the throttle cracked open just barely off idle.

So that is what makes the bike to pop and backfire is the lack of fuel? What about the spit and sputtering with the throttle open a little? Oh and thanks guys for the reply!

it meen that your fuel and air mixture is not right.

So that is what makes the bike to pop and backfire is the lack of fuel?
If the engine fails to start because the fuel won't vaporize, the raw fuel that didn't burn gets pumped into the pipe. If the bike then partially ignites a subsequent charge, that sets off what was in the pipe.
What about the spit and sputtering with the throttle open a little? Oh and thanks guys for the reply!
At first, then it clears up? When you hit the throttle very quickly? Worse the farther you open it?

go one size up on the pilet jet. It will start right up.

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