I would keep at it with wipeout, leaving it sit overnight for each application.
chuck had a thread a little while ago where he actually took most of a carbon ring out intake using wipeout - never seen that before!!
The stuff is tremedous, what i d however is spray the bore with amzoil first to get out any oiwder fouling so the wipeout doesn't have to eat throiugh that to get at the copper.
cat