Here's the quote from the KingCat assembly and operation manual page 42:

FLIGHT TRIMMING
"If the model climbs at high power and high speed add 1 or 2 (#4) washers under the front of the engine mounts to tilt the back of the engine down a bit more."

A little downthrust will make a definate change. Add one washer and test fly, then add the other washer if necessary. Don't forget to remove the previous down elevator trim.
Hope this helps.....

Harley Condra
BVM REP
JetCat REP