Back firing? Timing?

[TrashPanda4life]

I've got a 2002, with a 2008 engine, Airsal BBK, malossi head, tecnigas next R, 19mm delorto, stock airbox with a couple extra holes, oil pump removed, running 3%.
Put about 300 miles on this top end taking it easy, not letting it really rev up that high, to break it in. After that I found when I open it up, it revs really high, starts feeling like it's running lean, and then starts backfiring and just running like crap. I've checked for leaks. Described it to a couple people and they say it's probably a timing issue.
I bought a timing light from harbor freight. But haven't had the time and energy to get into yet. So, if anyone has any tips or advice, I will be very grateful. 

[Steve_h]

I timing light is not going to keep up at those high rpms. Once you  go past about 4 or 5k, you're outrunning it. Many won't stand that fast.

From your description, I take it that it takes off great, revs up and then almost immediately starts feeling sluggish and no power.
If this is the case, it's more than likely exactly what you said. It's probably running really lean. If you don't have enough fuel for ignition, the engine will continue to turn from its momentum and pump the fuel/air misture into the exhaust. After a few rounds of this, the mixture willbuilt up and then boom. Then the cycle starts over again.

If it's that lean, it's really really bad on your piston and rings.
Try covering the additional holes in your airbox and see if it helps. If it seems a little better, try covering about half of the air intake on the airbox with a piece of tape and see if it gets even better.

You didn't mention anything about jetting in your list of mods. It will have to be done with a bigger carb or different pipe. The BBK will most likely require it also.  the low speed jet doesn't really show too many problems usually since you are pulling a small amount of fuel and air. When you open it up, you are pulling lots of air and need the fuel amount to match. Extra holes in the airbox serve to help increase the airflow/decrease the vacuum which means a bigger jet is needed to supply the right amount of fuel.

When I got my 2001, someone had cut the snorkel completely out of the airbox and it still had the factory 70 jet in it. Needless to say, it ran like crap. I ended up buying about 8 or so jets and finally ended up on a 100 just from the vacuum crated by the snorkel not being there. 50cc and stock carb.

I realize this posting is a few months old. Hopefully you've got it sorted by now.

This place doesn't not seem to be very active for some reason.

[CROSSBOLT]

It has slowed down quite a bit. Good weather, better riding, less talking! Er, writing!

[Stig / Major Tom]

It has slowed down quite a bit. Good weather, better riding, less talking! Er, writing!

Yeah, and I've got chip-dip in the keyboard now.....and I think there's a filling in there, somewhere.

Shaking the bush here, boss!

Stig