Here's what the OS manual says about breakin on that engine:

"...only a very short and simple running-in procedure is required and can be carried out with the engine installed in the
model. For the first few flights with a new engine i.e. while the engine is being run-in set the needlevalve
for a slightly rich mixture not excessively rich as this may result in poor throttle response and cause
the engine to stope. About one-quarter turn open from the nomal setting will usually suffice.