JCB 3CX won't rev?

Hi, my 1991 3CX sitemaster does not get to max revs. For the first 2-3 minutes after starting it is ok but then revs slow down. I have cleaned out fuel tank, replaced fuel filter, engine oil & filter, throttle cable is ok, air filter cleaned. Any suggestions?
Mark, June 2023


done
Possible things to think about:
https://www.justanswer.com/construction-and-road-equipment/6xune-jcb-3cx-perkins-engine-will-not-rev-up-filters-clean.html

Specialist forum:
https://www.heavyequipmentforums.com/tags/jcb/page-2

Dndhdh, June 2023
link Click here to see other fixes for JCB 3CX.