Another area that you should also look at is the back plate assembly. If you are down on power, sometime it's because there is oil residue built up between the disc valve & the back plate. Disassemble the disc valve from the back plate & clean the parts with denatured alcohol. After re-assembled, there should be slight friction between the parts.

Do a search on You tube, there are three links on Naruke showing how to clean the back plates on a 170DZ at a local Japanese flying field.

Adrian