[Healeys] Carburator needle changes

[Jerry Costanzo]

I have installed my HD8 carburetors onto a slightly modified BJ8 engine.  The
carburetors were rebuilt (by me).  At present, the engine runs well but the
carburetors have a little backfire when cold and occasionally when warm.  They
test by lifting the piston to be too lean.  If I adjust the fuel mixture any
richer, the idle goes over 1100rpms and I still don't get the lift test to
properly keep the rpms steady.
Other items of note:

Checked for vacume leaks.  Did not find any with a unlit propane torch.
Timing appears to be correct.  I went back and checked the valve positions vs.
cylinders at top.
Engine revs ok,  I have not driven the car to test the power.  It does not
have body panels on yet.

Is it time to try a richer needle in the carburetor?   If so, which would you
try?

Jerry
BJ8  in progress
BN4