try a fox miracle plug or OS type F just a guess. martin
I use the OS f in all my 4 strks 30 thru 91 no issues have not used a fox but read its ok

In the moth I would guess the engine inverted thus tank height important pickup even with carb also
the TT is it a single needle with air bleed or true 2 needle carb?? if aire bleed hole about 1/2 way on carb
ith true low speed adjust start 1 turn out from closed if you can turn plane upside down to get engine upright for adjustment and an on board glow heater may help too