Find out if a high compression piston was used. If so, run away.............fast. A very well document problem occurs when a high comp piston is used in these motors. The increased compression will cause the cylinder head studs to start tearing themselves out of the cylinder, and the first sign of this will be a head gasket leak, which may sound like a valve tick, or the sound heard when a spark arcs. There is a fix, which requires removing the cylinder, then drilling and retapping the holes to accept larger studs. It can be a little pricey if you don't have the mechanical know how, so I would suggest looking for another quad.
2012 CRA Senior II champ
2011 CRA Senior II, Buckeye series, and True Grit series Harescramble Champion
2009 CRA Senior II, Buckeye series, True Grit, and Salem MC Harescramble Champ.
2007 CRA Senior II, and Buckeye series Harescramble Champ.
2003 Lonestar 250R
2001 Lonestar 250R.....now a 310
1986 TRX250R (restored to new)
1986 TRX250R (still in pieces)