Unable to screw the gas cap back on my clk320 after putting gas in the tank

Possible kinked or clogged vent tube. Either on the filler tube or the vent on top of the tank. Causing back pressure.

Brother John, you've removed as much as you can for access to the filler. Remove the hose clamps/bands that secure the fill tube and vent tube and then remove the screws around the gas cap that secure the fill tube to the body. With the gas cap off, go below and pull the hose and filler neck down and work the hoses lose with a pair of channel lock pliers and sticking a screwdriver between the metal tube and hose to break the seal. Put on the new filler neck and stick it back up in the body and put the screws back in. THEN put the hose clamps back up and tighten them, put the gas cap back on and your done.

What am I missing? Go to the station and put some gas in the tank. Drive to the auto parts store and buy a cap. This may trigger a check engine light as the computer senses a fuel system leak. Some autoparts stores can read check engine codes, and can reset the light.

Sounds like you have something stuck in your gas tank maybe someone put something in your gas tank perhaps you might consider a good flash light and a pen open the cap insert the pen hold tight and put flash light in filler neck flap hole to see what kind of obstacle you have stuck in your filler nozzle neck if your unable to see anything you might consider taking the car to certified technician for service to you clogged gas filler neck.

first take gas cap off to allow vapors out unbolt the traps off the tank have a jack under the gas tank to hold it up.when straps are off make sure to remove the wire's off the top going inside to tank.then slowly lower tank down then pull it out from under car then get a hammer and a screw driver flat head use this to slide the lock on top to remove it then pull out the pump and replace with new then put back on.

Sounds to me like either the cap or the neck it screws onto is warped or malformed.
You can try another cap.
If I was you I would take it back to the store because that is not normal. My Poulan has a cap that is nice and loose and goes on with ease.
It should not be hard to put the gas cap on.

My guess is you have a leak either in the fuel tank itself or in the plumbing from the cap down to the tank. Have you ever been in a wreck?

When fueling the vehicle, do you see any gas leaking out under the vehicle?

Does the area where the gas cap screws in have any damage that would allow a leak to occur?

Another area to look at is the system that recycles gas fumes back to the gas tank.

Something is not allowing the tank to hold pressure.

You are probably not going to find assembly instructions. If you can't find all the parts or screws then get another cap. Google " motorcycle salvage yamaha " and you can probably find one at a much lower cost than the dealer would give. By the way, forget any loose screws in the gas tank. The stuff can not get past the fuel valve and filter and are not going to hurt anything.

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first take the gas cap off for a few minutes and where the hole is to put the gas into the tank open that up with a screw driver for a few minutes and once the car starts put in a half a tank of gas in it and a bottle of STP gas treatment with fuel injector cleaner and a little more gas and if this helps you should be good and you may have to replace the fuel filter if it does not open it all the way be sure to put the gas cap back on after truck starts