ORIGINAL: JPMacG
I just purchased two Thunder Tiger GP-28s. These are ABN tapered bore engines with bushings and air-bleed carbs. The directions for break in from Thunder Tiger say to use fuel containing 25% castor oil and break them in at full throttle in a rich 2-stroke setting. Hmmmm.... sounds familiar.
I try not to re-educate the people who are not willing to learn, or to stubburn to change. I have yet to have an ABC engine that ever looses it's pinch. My Tower engine that I am putting back together currently starts pushing the sleeve out when there is still about 1/4" stroke left, and that is after close to 20 gallons, and I break them in WOT.