did You just bung it on
or set it up correctly squish / compression ratio etc

 

That is weird. I’ve had a few RK heads. Each one has done its job. Definitely check everything is set up right. Also check what is etched on the head as that’ll tell you what they’ve done to make it, they make heads from mild to wild. You could also drop them an email with the info and they will be able to help and advise.

 

I measured the squish and its sitting at 0.98mm. it has 300 13 stamped on the insert.

 

did you get 3 inserts with the head?

higher compression doesn't mean more power. it gets to a tipping point where it ruins your top end power or can make it peaky.

for a 300 I like 1.3mm squish with a 25cc

I had a 125 race bike in few years ago (Jamie dobbs) ... for a normal rider what a pile. almost unrideable power delivery. it reminded me of the old TZ stories. did nothing till 10k+ with a 1500 rpm window of power at the top with no over rev. it was all in the head set up. modified a stock head and had strong power through the rev band

it did go to show how good he is keeping that thing on the boil!