won't pull past 5000rpm

[30psi]

Originally Posted by datdrift

that is the problem, the idle's sorted, but it cant pull the higher revs on full load without hesitating and spluttering

I was gonna ask this very question.

If it will go past 5,000rpm on light loads then the problem is most likely to be fueling. Either too rich or too lean.

Does it sound like a rev limiter or is it more severe and just a complete loss of power?