I have a (Wassel) Concentric and it needs to be moved a bit to the rear in order for the float bowl to stay clear of the magneto, hence the replacement of the studs with longer ones.
I run a 628 currently on the M20 and it has to go back 2".
When in this position there is not enough space for the pill box air filter to be screwed on, or better still it can not fall off.
The filter backing plate is attached to the carb before fitting then the filter perforated strap and end plate assembled to the carb after it has been bolted to the bike.
Down side is the throttle cable fouls on the tank bottom so you need something to keep the cable bent to a smooth 90 deg bend.
Originally I pinched an outer cable ends from the Yamahas .
The other thing to be wary of is water. You will need something. even if it is just a tight fitting O ring to divert the water that will run down the outer then through the adjuster, down the inner down the needle then fill up the bowl.
This happens even when you are riding through rain.
The other thin that caught me out when I made the longer studs is the stud holes were not parallel so the studs got further apart requiring some mechanical rectification with the oxy torch after the loctite had set.
A friend thought he would bend the studs cold and ended up breaking out the stud hole in the head.
Damn right it is fixed!!!
Lost my head a bit and kept thinking of the concentrics on my Bonneville which are from the first year of manufacturing (by this time resleeved of course) and thus have a sdrewed in jet.
You'd better check it...Newer AMAL Concentrics have the removable pilot jet reinstated...I'm not sure about the Wassell version...
If it has the removable jet follow the settings for an Amal monobloc from 1954 onwards...Ian
Ian, the new Wassel concentric-copies have the pilot jet fitted from the outside opposite side of the air adjust screw. Easily accessible and replaceable.
Quite a different story from the first year concentric with the pilot jet fitted from underneath the housing, inside the float bowl. Later of course they replaced the jet with a bush, but kept the threads. Some confusion before I realized I hade no pilot jets, it ran a tad on the rich side with just open holes right through...
But that’s the Bonneville, the M21 have a brand new Wassel. Runs good but still some sorting out.