Hi have 1982 xr3 carb non injection , for a while now in 3 rd and 4 the engine wouldn't rev out it would sputter and pull back with engine pinking.the over day it was hesitant in all gears . We checked the fuel filters and turned the ignition timing slightly until it was ticking over and revving better and no pinking. Took it out for a run and the car was much more responsive, no pinking and pulled much better in all gears. After about 2-3 miles the engine lost all power under 4000 revs just spluttering and holding back but you hit 4000 and it pulls as it should to red line . Have moved timming back same thing happens and moved it advanced and retarded same thing runs great then problems return .any thoughts