I'm glad this oil problem has popped up again.
My 06 Uly dumps loads of oil into the airbox too, even after copying a genuine Maz breather setup, with all the pipes running identically, I too had a airbox and intake literally swimming in oil after doing a 200 mile charity run. I have now just blocked the holes in the base plate, and run 2 individual pipes down to the belly pan. I'm fed up constantly battling with hose re-routing and buying hose. Fuck it, problem solved.
Now for your misfire problem,
1. service the engine.
2. check your ignition timing.
3. do a TPS 'Hard reset'.
4. check your intake seals for leaks. I have just changed my intake seals and it runs generally better and 'tighter'.

Now, does your fan come on even while doing a steady a 70mph run?

Are the two holes you blocked up the two inside the air filter

How many miles on the bike. Is it an XB

Dutchman, if you're talking to me then, Yes, I blocked up the two holes in the airbox base and Yes, it's a 10,000mile, XB12X.

Hi Lands yes I was. My bike is a 06 Uly as well

Dont know how it came about but the old breather holes, inside the filter, should have been blocked up in the first place. This stops dirty air and other crap being sucked up into the engine.

What you have done now is the right way for this mod. One thing though. Just be 100% sure that whatever you have used to plug the holes can NEVER get sucked into the engine or you will have a very large bill if they do.

Things like grommets, tape, etc are not good enough IMO. I used a single piece of tube, about 200mm long, pushed into both holes from under the base. It can never get into the engine.

The only logical place the oil can come from, in the airbox, is the breathers. These, as the name states, are for the engine to breath. It should only be venting oil and water vapour. There should be no oil in the airbox at all. The "draw" of the engine pulls this vapour back into the engine. If you have an oil leak, from say a cam in the head, it will pull that in as well.

The idea of the breather mod is to stop the engine trying to burn this vapour and it works 100%. The OEM system is only for emission regs. Any solid oil being pulled into the engine, via the air box, is going to be a problem.

You could try.
1) To check for an oil leak have a static, hot engine, pressure test done.
2) Do the breather mod but run the hose into a catch can, for the moment, to see what is coming out of the engine.

And/or seek pro advise. One thing I will say though, to you and everyone else with rough running engines, is that the XB engine will run as sweet as a nut because mine does and so should yours.

Sorry for delay, working nights...
Ordered plugs, leads and coil. Plugs and leads arrived first so thought i'd try them .
Problem sorted.
Ticks over , less vibes and feels better than i ever remember? Nice blat down the A24 reminded me why i bought it.
Came out the next morning to a FUCKIN PUNCTURE.

I give up .

The oil thing does seem excessive, within 100 miles its making its way onto the left hand crank case. Will try the catch can to see how much its losing.