4200 RPM AND THAT'S IT !

hi chaps, this is how it stands, i have removed inlet manifolds,plenium chamber ,injectors, cam covers,injection system .repaired the exhaust manifolds,removed electrical plugs from advance units to check wire terminals, replaced vacuum pipes water pipes,fitted new oil presure sender unit,replaced spark plugs, and all ht leads ,new fuel filter, air filter oil filter, refitted components with new gaskets,seals etc, now she starts first time runs very smooth, very sweet ,but i when on the road i can only get 4200rpm out of her,even if i accelerate slowly 4200rpm and she holds back with a slight missing ,but when shes stationary it will free rev to 7500rpm, iam standing still now and scratching my head, any help thanks (mondial 30L QV,1982, engine number 00052)

 

THANKS,thats why i changed the filter etc,but as soon as you come off the pedal and drop beliw 4200rpm its back going again,