Oversize powervalve cover.
 

Have just bought a oversized powervalve cover and was wondering do you plug the middle threaded hole that looks like it goes through to the barrel? or leave it open?

Bike is a 02 300.

should be bolted,the stock one also is bolted in the same spot

Ta, thought it should be but thought it would be better to ask rather than just blindly do it.

power valve cover
 

what does an oversized cover do ?

Some oversize covers don't have the center bolt like the OEM one.
In this case, leave the bolt out.

Theory is it increases your bottom end power by increasing your volume of the power valve chamber. In other words gives a bit better throttle response down low. Good for real technical riding.
I put a Trusty cover on mine. Not really sure if it's needed on a 300 but the damn thing won't stall now.:D

I'm not a fan. Dulls your low end throttle response but fattens the torque a bit, great for guys with less than perfect clutch ,throttle control or who dont like crisp zippy power.

Power Valve cover
 

The hole should be plugged or preferably a drain line attached. I used a zerk fitting with the center drilled out and added some tubing.

Some oversized covers have a vent tube attachment at the bottom - some don't...

He is referring to the one in the center of the cover that goes "into" the cylinder - it's for a mounting bolt.

Adding a PV cover helps more or less depending on the pipe you use - given that it adds volume to the exhaust - adding it to an already large torque pipe like the fmf gnarley or fatty isn't as notice-able as adding it with a doma or messico pipe, etc.

It provides gain on bottom and doesn't effect top end - as this chamber is shut off when the power valves are open (high rpm).

Jeff

Dulls? nope,, adds bottom end by adding volume that becomes a non issue once the pv opens. Never heard of it dulling the bike down.. gives it more grunt. odd you say that.. On my 03 it was needed,, the 03 was very weak off the bottom,, I did the big cover, messico pipe and a cdi from an 01 300xc and it was good. Oh, and ltr jett and special reeds I got directly from the boysen shop down the road.