Chevrolet: 1986 Caprice Classis not starting., caprice classic, valve seals

Question
Me Warrington,
I have a 1986 305 caprice classic.  The owner before me put a large edelbrock carb, can I change that.  It also ran for about 3-4 weeks as long as I didnt go over 40mph.  Lots of white smoke comes out when it's started and then again once it warms up and I go over 40mph.  You can also hear a rattling nios ewhen you go at the higher speeds.  I just had a complete tune-up, and a head gasket replacment.  thst worked temporarily but know it wont even start,
PLEASE HELP!!!

-Billy MArtinez 919-449-5544  

Answer
BILL;
HI  I would have the cyld. psi checked, to see what type of pressure you have,or if the valve seals are bad, as far as the big carb. yes you can change it to a smaller size carb, but if there is a aluminum intake manifold on it,I would keep that on as it will save you gas and run better.
also check your oil dip stick if it has any white stuff on it than you have water in the oil, and check your radiator if there is any brown oil in it than there is a crack in the engine or a bad gasket , but I pry that there is not , and check the spark plugs to see if any are fouled . than you will know what cylinder it is or valve etc. ok