I'm about to go look at a 1999 18 ft. viper cobra (90 hp motor, not sure yet what brand) in the next week or so.  I understand that i need to have a mechanic check it out and all that GENERAL used boat checklist stuff.  Can NE1 tell me NEthing specific to look for when looking at a this boat?  dont know too much about vipers.

I'm pretty sure that NE1 is not a member of this forum, but others may be able to help you. 

I can't speak as to the quality ( or lack of) on Vipers, having never owned one. I will say that if you ever intend to get it out of the NO WAKE zone, you're gonna need more than a 90 on the back of it. It may end up being a good platform, but will ultimately be an underpowered pig.

John Storey built boat.  (former Champion founder).

It's a worked splash from a Ranger 481 IIRC.  Fast boats though 90hp isn't going to get you anywhere quickly.  As always, check the motor with a mechanic, transom and flooring for soft spots.

Check for stress cracks, make sure the transom is solid, check lower unit oil and of course have a compression test done on the motor....this is just a few things from a very big list.  Honestly I would take it out for a ride and see how it runs with the 90.  Sounds very under powered to me with a 90.  You may have a problem getting on plane with two people in the boat, fuel and live wells full of water.  A friend had a 17 foor Nitor with a 75 horse motor and I would have to get out of my seat and sit on the front deck so that he could get on plane.

I'm pretty sure that NE1 is not a member of this forum, but others may be able to help you.

NE1 = anyone

90 hp is one of my major concerns.  I've spoken to some people who know the boat and owner.  they say the boat is in perfect shape.  he's asking $6500.

$6500 for a grossly underpowered boat?

Way too high.

just talked to the owner...its a 125 merc ...not a 90.

125 is definitely better, although still a bit underpowered.  I was looking at boats for a while before I purchased one.  It always seemed like underpowered boats were a tough sell. Offer him 5K and take it from there.  Check the NADA value on line.  There are some good deals out there.  Viper's are pretty sharp looking boats.  Do not know how well they ride.  Good luck!