Motorcycle Repair: 1986 xr600 Honda, burning oil, air filter

Question
I just purchased the bike.  It needed rings, because it had low compression and burning oil.  After rebuild, at over half throttle, it acts like it is losing spark or fuel.  Took air filter out and side cover off, it runs great, leave filter off, put side cover on, it acts up again.  I revved it up and I notice the side cover being sucked inwards at high throttle.  Thank you

Answer
Philip,
these engines have lots of vacuum and so need
lots of air available through the intake system.
If it has trouble getting the air into
the air filter box it might suck the cover like
that. At the back of the air box there should
be a plastic fitting with holes going down,
this is where the air comes into the box.
Check and see if it is plugged up.
You need to make sure it can get air into the box
behind the air filter somehow.
Make sure the air filter is not too oily
or dirty.
The filter has an insert to help it keep it's
shape. Make sure it has that as well.