The A10 carb is almost identical to the A12 carburetor.

If the float level is correct, you won't need a new float needle valve. If the valve is bad, it fills up with too much gas (you'd see it in the sight glass).

It sounds like one of two things:

1. Fuel is siphoning into the bore. There is a check ball on one of the circuits to prevent it. Also torn or misaligned gasket might cause this. But a blocked air jet can do it too. The air jet not only leans out the mixture (while aerating the fuel), it acts as an anti-siphon effect too. Remove the air jets and spray them clean with a spray cleaner (make sure they are not blocked).

2. Fuel is running into the bore. If the power valve is bad this can happen. ditto for gasket problems.

Dodgeman, does the A10 Hitachi carb have the same kind of power valve as the A12 Hitachi carb?

Check out this article, and examine the carb carefully: Carb adjustment, troubleshooting, rebuild and inspection

Or you could perform a sub-aircleaner-ectomy. This means removing the air cleaner, replacing everything underneath, then putting the aircleaner back on. Just kid'n.