Grey is prolly right on needing the carb cleaned, but you might try this first. Turn the petcok off. Get a container to catch fuel. Take the fuel line off the carb. It should lose about a teaspoon full of fuel. Now, holding the fuel line over your contianer, turn the petcock on. You should have a small steady flow. if not turn it to reserve and see if you have a good flow.
If you have a bad flow there you have gunk in your tank or petcock or maybe in a filter.
If the flow is good,it is carby time.
Can you post a pic of the ped ?