If you use the old metering diaphragm it could be the problem as a stiffen one can hold the metering lever partially open. It would also advisable to pressure test the needle/seat area as I had a few clones to leak around the seat.
As for being a clone it is more likely a Zama clone as I haven't any Walbro clones in my area. When I looked up the metering for the Makita it does look like the Walbro version.
Here is a link to the parts manual.
Makita EBH252L IPL
