It's a breather problem. Has to be. It's the same problem you get on a normal bullet if you get the breather hose trapped.
If it's pressurising the oil tank, that's all it can be. With a functioning breather hose, any pressure that builds up in the oil tank will vent to atmosphere.
I'm not directly familiar with the electra X but looking at our hosts parts diagrams, it's exactly the same setup as my late model 350 bullet came with
In use, the crankcase pressure vents into the oil tank through a small hole. That pressure then passes out through a stub in the top of the oil tank (that stub is vertical). It vents into a cylindrical catch-can via a duckbill breather inside the can. Any gas vents to air through the gauze lid of the can. Any liquid runs back down a second hose (which has an internal non-return valve) and into the timing chest through a horizontal stub.
Couple of things. As has been mentioned, this system is not very effective and is prone to becoming blocked by large quantities of emulsified oil (mayo). Another thing that would totally banjax the system is if you inadvertantly attached the return hose to the oil tank breather stub. It has a one-way valve in it.
My best suggestion would be to remove the entire breather system and give it a good blow through. It isn't wrong to simply remove the catch can setup altogether in favour of a more traditional duck-bill breather hose attached to the end of the oil tank breather stub and blank off the stub in the timing chest. This will make it all a bit more free-breathing. I made a little aluminium bracket to point the end of the breather hose at the chain just above the gearbox sprocket.
Hopefully, there should be a picture of the mayo in the standard catch can on mine below:
This is still inadequate compared to the original sysatem of breathing directly from the crankcase. On mine, the breather hose would still clogg with mayonaise periodically resulting in a drop in power initially followed by oil seepage if it got totally blocked. Happily very simple to remove and blow through when set up like that.
An odd finding is that the mayonaise formation TOTALLY stopped when I fitted a Hitchcocks pressure relief valve on the scavenge side. Prior to that, I got regular mayo blockages, even when I was averaging 150 miles per day on a 3 month tour of Britain. Make of that what you will
I finally radically (and bravely)re-jigged the whole breather system by drilling a hole and fitting a stub into the crankcase itself, attaching a long bit of microbore sitting vertically behind the engine then routing it to the back of the bike via a diesel fuel line non-return valve. This breathes out around ten times the volume of gas if the oil tank is allowed to breathe freely through the stub (the oil filler caps on the older models are not sealed). It's my considered oppinion that the best way round this whole breather problem on catch-can equipped bikes would be to have the engine breathing normally out of the crankcase via a non-return valve (either mechanical or a simple duckbill), to have the hole between the crankcase and oil tank blocked off and to allow the oil tank to breathe either via the existing stub or through a small hole drilled in the filler cap.
My breather mod should appear below. Obviously, this is a radical step to take, the duckbill hose on the oil tank stub worked well enough, just not as well as it could do to my mind.
Here's the youtube video of me measuring how much the engine was breathing:
https://youtu.be/ET0Rv4fh-Yc
