When the Airscrew is screwed fully home, the engine should stumble and conk out, so its either needing cleaned [ as Airhead says] ,OR. the pilot jet is too small,
Yip, its Grampian Motors, liverpool. just send the crank, they have all the parts, same with a rebore, just send the barrel, they measure true, and bore the size required ,
http://www.grampianmotors.co.uk/
When i"v built my DT"s they spin smoothly and free, untill i install the new crank seals , then they go tight,,, ,is the rod got play,? this is important,
Most DT"s have one shim, on right side, [ primary gear side], But, i have build 3 engines, and none had a shim on the crank, they say its when tightening the primary gear - it pulls the crank to this side , and the shim gives clearance. , ,all my engines had never been apart, = & no shim,