classic motorcycle forum

You don't say if the carb is flange or spigot mount, if spigot mount rotate the carb until the float chamber connection is just slightly high and the float chamber horizontal
If flange mount then rotating the float chamber will ensure the jet is flooded but the float can bind
I have seen installations with additional drilling which supposedly improve things, but basically a horizontal jet doesn't work great

E.J.Massey left Massey Arran and went to F.J.Coopers where they produced the Massey. Early in 1924 he sold out to R.L.Jepson.  He was then briefly with H.R.D in late 1924 and early 1925

The BTH mag dyno shown was in use by a number of manufacturers until the mid 30s. It puts out a snarling 4 amps for 24 watts, regulation is by a four position switch mounted in the headlamp. A BTH cut out was fitted in a separate housing usually mounted on the top of the tool box or on the frame. As pointed out in another post, pretty much any wiring diagram for a 3 brush dynamo will get you close, I doubt your Miller headlamp is original, but if it has the 4 position switch can be made to work. Original headlamp usually supplied with the BTH unit was the Powell and Hamner, I believe they merged in about 1926

Nigel,  I'd also be checking the nuts holding the gearbox and mounting plates
Best,   Chris Mac

From my understanding this is the only Grigg with a  B H engine, i'm aware of only one other V twin Grigg , here in California, which has  a 750 Blackburne
John Kidd is very knowledgeable on these bikes

John
Binks certainly made carbs for a variety of cars, this one is 30mm
Best
Chris Mac

Smartfella
Some pics of the Burman spacer