BMW F650 FUNDURO 1994. My fuel filter (not that under carbs inside T connector-but the one after petcock a seethrough plastic one) delays a lot to be filled up with gas and as a result my bike shuts off! I have replasced it by a new one but nothing solved!!

fuel filter is in the petcock where you turn the gas on and off

There isn't one. You have to put one in-
line

The threads are bad. If you cannot get under the head of the plug or use vice grips to pull it out, then you are going to have to remove the whole sump pan.

On a carb model, a lot of times there is an inline filter in the line from the gas tank to the carb, so follow your gas line down.

BUT, a lot of times, there is no inline filter, and the only thing you have is a filter screen attached to the top of the fuel shutoff (petcock) inside the gas tank.
The only way to access is to drain gas tank and remove petcock,

Usually when you find gasoline in your crankcase it's because your carburator is leaking fuel into the cylinder heads. From there it goes into the cylinders on top of the pistons. Down past the rings into the crankcase. If enough gasoline goes in there, it will go past the sprocket shaft seal and into the primary case as well.

This is normally caused by a bit of trash getting under the float valve in the carburator. But, on a 1996 model, there is supposed to be a vacuum operated petcock. The petcock is supposed to close whenever there is no vacuum on it that is supplied from the intake manifold. Either the petcock has been changed, which is not unusual since the petcocks were quite troublesome, or it is not working properly.

First, you need to clean out the carb. and get any trash out from under the float valve. Remove the carb from the engine. Take the float bowl off the bottom of the carb. Pull the pin out that holds the floats and remove them and the float needle valve. Blow compressed air through the fuel inlet fitting to clean any trash out of the fuel valve seat. Inspect the needle valve for damage, replace if necessary. Reassemble and reinstall the carburator. Check for proper operation prior to starting the engine.

With the carb cleaned, you can install either an aftermarket manual petcock (Pingel) or a Harley petcock for a 1994 or prior model. These are manual petcocks. When you're not riding your bike, turn the petcock to the "OFF" position. Also, install a fuel filter in your fuel line between the tank and the carb. Get one of the good ones with the scintered metal filters in it.

Change your oil and filter. Check your primary oil as well. Change it if contaminated with gasoline. Before you reinstall your air filter, connect the fuel line to the carb and turn the gas on. Closely watch the inside of the carb throat to see if fuel starts to "bubble up" into the throat of the carb. This usually takes a few minutes so be patient. If it does, you need to replace the float valve needle with a new one and check the float setting. If it doesn't "bubble up" you're good to go. Then, don't forget to turn your petcock to the "OFF" position when you quit riding the bike.