Twin SU's are a pretty good bang for the buck. pretty good economy even w/richer needles. A set of twin DCOE webbers can't be beat though.

Road and Track Magazine added a set of Webbers to a stock TR4 and only gained 10 HP for a $2000 investment.

The SU is a simple elegant design. That said, it suffers from cheap materials and needs constant care. The biggest, hardest to solve problem is that the cheap metal in the throttle body wears out where the throttle shaft goes thru. That lets air in at the shaft and the misalignment of the shaft keeps the butterfly from seating properly in idle position, making idle adjustment difficult. Not a problem for racing machinery.

There used to be a tool for boring the throttle shaft hole so that a bushing could be inserted.

Need float level spec for 1980 620 truck.

Having trouble setting it. Just a little adjustment gets me no fuel or a very hig level.

Having trouble adjusting idle also.

Bought rebuilt carburetor. put new filter on intake side of fuel pump, but got rust from fuel pump into carburetor.. Was able to blow out most passages w/o disassembling it. Runs now, but wont idle. Suspect Idle circuit is clogged.