My friend recently brought a new X30 and thought 50:1 ratio meant 50mL of oil per 1L of fuel. So for 5L of fuel he would mix in 250mL of oil, instead of the 100mL.
What could this do to an X30 engine? If someone were to do this over multiple race meetings and practise days ever since running the engine in, where would the loss of time be (low end/top end) if any, and what kind of damage (if any) could this do to the engine?
That’s sounds like the correct amount of oil at around 20:1.
An x30 should not be running 50:1
I would never run an X30 with 50:1 more like 25:1/20:1
His error actually probably saved his engine. 
As others stated it should be around 20:1
https://www.iamekarting.com/manuals/
X30 manual says 20:1 (50cc / 1 l). Remember, you’re trying to make a soft aluminum piston slide against a rough iron liner that expands a third as fast at piston speeds that exceed those of F1 or NASCAR. One bottle oil to one drum of fuel is appropriate.
While everyone who responded is on point, to answer your question what would happen if you had too much oil in your fuel depends on how much oil. Remember oil is combustible and while certainly not as much as gas it still burns…to a point. Too much oil would likely foul the plug and cause issues running. That would be the most obvious clue, if you kept changing plugs you would have performance loss more so on the low end but all across the rev range. Would this damage anything? Other than your pride, Likely no.
However, too little oil, as others noted would be much more catastrophic. With little lubrication, the damage would be done fairly quickly running at race pace.
Oil also displaces gas, so your carbs needs to be adjusted when taking wide swings with oil ratio.
@Charles_Kaneb , in college, we had a sophomore design class where you had to draw up a 2-stroke air piston engine and then build it in the machine shop. It was a steel piston inside a steel cylinder that had to run around 5,000rpm to pass. Once you hit that mark, you were free to hotrod it, and I went all aluminum. That, with some other changes made it really scream (something like 9k). When I added just a drop of oil to the intake through the oiler, revs would jump to 12k and then quickly come back down. I learned a lot of valuable lessons about aluminum galling and how oil helps seal a piston, haha. It made me feel right at home running 8:1 with the Comer
That tracks because adding oil will lean out the A/F ratio. Power will likely be down however. What you said about ring seal due to oil is definitely a thing. I remember reading about a was a test done in the 70’s or 80’s where power kept going up as oil was added. I think I was by a guy called Eric Gorr.
This was with a compressed air engine, so no combustion. It was just hooked up to an air compressor, so the oiling experiment was really good because there were fewer variables. The jump in revs were purely from a better seal. The galling was so bad you could see grooves up and down the piston, and you could tell the blow-by disappeared when oil was dumped in.