Welcome to this forum! Andres, from the minimal info in your post I must assume you are new to all of this. You do realize the clutch is either engaged or dis-engaged. You cannot feather from a dead stop. You must pedal up to a reasonable speed before engaging the clutch.
Easy common suspects relating to your described symptoms may be a couple things not clutch related.
First. If the fuel cap on the tank is not venting properly, the engine could be fuel starved. With fuel in the tank and the cap on tight, remove the fuel line from the carburator and stick the end of it into a fuel can, turn the valve on to see if you have a steady, uninterrupted flow of fuel. Give it a couple minutes. If fuel supply seems fine the Cap is venting properly. If the flow slowly turns into a trickle then drips to a stop - remove the cap to see if a good flow is restored. THE FIX is to drill a small hole 1/16 or less in the center of your cap. If this is not the prob----Then we'll move on to something else.