Mountain Biking - fork/handlebar vibrating.

Here is my story :D. I switched my stem like a month ago for a stem with a steeper angle. IT rode fine. Got a longer seatpost with setback and rode a week. I decided to try the old stem back to see if i needed it that high after i got my seatpost to see what was most comfortable and for some reason i feel a front/back shake in my handelbars when i go over bumps. When im on flat i dont feel it. I thought maybe i didnt but the stem all the way down so i loosend the bolts and pushed it down while i tighten them again. No go. Anyone have any ideas what it may be. Can it be my headset? ITs a WTB venom comp. Thanks for your help.
BTW IVe only had the bike since march so i dont think its ovalization on my head tube

Headset is loose.

Can i tighten it myself or does it require special tools?

Can i tighten it myself or does it require special tools?

Just allen keys. No special tool required.

Since it seems you are not sure how to tighten the head set here ya go;

1) loosen the bolts on the stem

2) use allen wrench (usually a 5mm, 5.5mm or 6mm) and slowly tighten the bolt holding the stem cap. Tighten a little then check for play (hold the front brake and rock the bike back and forth). There should be no play. Once you have no play then lift the front wheel off the ground and the bars should spin freely without binding or grinding. If there is resistance then the cap is to tight.

3) be sure bars/stem/wheel are stright then retighten the stem bolts and your good to go.

Be sure not to over torque the cap bolt or you could ruin the head set.

FYI for stuff like this you would get more responses if you put it in the Mechanic forum.

:beer:

you may need some spacers if its still loose after tightening

Thanks for the responses guys.

"FYI for stuff like this you would get more responses if you put it in the Mechanic forum." will do next time.
Thanks again.