8v gigifant yeah?
How much fuel does it have in it when its playing up? I had a lift pump issue that was only a problem with low fuel level. Its got to eother be a spark oor fueling problem. How old are the plugs/leads/dizzycap, are they in good nick and free of moisture?
Does the stuttering clear allways, or is there a constant lack of power? what sort of RPM does it happen at?