So I buy an intake manifold from online. It is made by obx Racing. I have it decked to make sure it is straight, I install with heavy duty gaskets, tighten it down as much as possible and still have leaks, very slight but enough to make throttle jump from 1000rpm to almost 2000rpm constantly instead of nice steady throttle. any suggestions?

I would pull it out and reinstall. Make sure to fully remove prior gasket and make sure all lines and hoses are where there supposed to be and still in good condition.

First off, I'd be wary of OBX products. Second off, you can't tighten the nuts as hard as you can. You need to buy yourself and manual. They are torque listing and tightening sequences in there for a reason. What you are doing is tightening the nuts so tight that you are crushing the gasket. The torque for those are not alot, I remember from when I took mine off. So go get your self a torque wrench, a manual, and a new gasket. Also OEM honda gaskets work best they are usually less than 10 bucks.

Make sure both mating surfaces are level and clean.
Place the gasket on the head,
Slide the intake manifold onto the studs.
Tighten all nuts just enough to keep manifold in place (hy hand).
Pull out the tightening sequence diagram and locate number 1
Tighten the first nut down to factory spec.
Repeat for the remaining nut.
When done, do over then again in the same sequence (somtimes they loosen themselves) It will not feel like you are tightening them alot but that is okay. Also it doesn't hurt to check again after a couple hunded miles.