hi , another question to anyone who can help!
1959 belvedere with a 318 , runs and idles fine but when it reaches around 2-3000 rpm it splatters and runs very rough . ive had it on a machine which is diagnosing that at those rpms the mixture leans right out. ive had the carby overhauled , replaced the manifold and gaskets ,checked for any external air leak but nothing was found. does any one have any ideas as to what could be the problem ?????  cheers!  

change the fuel filter and call me in the morning.  

Fatten up the carb.
Jets and rods for a carter 2brl?
Then again where's the timing set at? Try 32* at full advance and see if it craps out still.
But it does sound lean as hell, which is how those 2brl carters come, LEAN.
Bigger main jets would be good.
And make sure the rods are lifting up upon full blade opening.  

I worked at a Plymouth Dealer when these were new and they were bad then.  The timing advance used then for emissions was part of the problem.  The spec was TDC at idle.  Pinging was a problem with too much advance.  If your using the stock dist, try 2-3 deg BTDC.  The best fix for this is a new Mopar Performance dist and use the 32 deg max as suggested.  If you want to stay with an early dist use one from a 67 and set the timing at 10 BTDC.  I know it's a Poly dist, but I think it will drop right in.  A 273 dist from 64 to 67 will also work.  I did this to many cars back then to get rid of the smog timing curve.  The carb's were also a problem.  One size up in jets as suggested will help.  Set the accelerator pump for max throw.  Stretch the spring for the piston that pulls the rods down.  Trial and error on how much.  The factory lenth of this spring causes a delay for enrichment when accelerating.
Don  

hi don , thanx for the info , ill give it all a go , cheers mate