D10 engine in my D7 has started four stroking at low revs. Any thing below 40 mph in top she chugs along. Higher speeds OK. From about thirty she pulls like a dream and with open throttle runs as she should. Slow down and try to do 30 she four strokes again. Fuel problems or carb seting , maybe timing ? Griff
Four stroking usually means too rich mixture.
Plug a nice light brown colour. Dropped the needle a notch to see if that helps..
I'll give it a tootle to-morow... :-\ Griff