over fueling

[flyingbanana]

ive had this problem for a wee while now and cant seem to get it better.......the problem im having is the car uses way to much petrol ....i can spank 2 gallons in less than 28 miles..........the carb has been fully stripped and cleaned and new parts added the only part that hasnt been replaced is the air corrections,idle jets,mixture screw and the jets/holders etc..the whole engine has been fully stripped rebored and new parts put on also the head has been completely sorted...unleaded,doubled valved,new guides etc

 

just keep getting black plugs if its too rich but im only 1/2 a turn out from base...even if i screw it all the way in the car still runs...........would their be a fault with the mixture screw?

 

the carb still has all original jet sizes for the 1600,oh i have a 32/36 5a manual choke

 

any ideas