RE: JBA engines, good or bad.
I broke in and test flew BigEd's first JBA .56. I was writing for R/C Report at the time and live in Florida, whereas it was winter in Omaha where he lives. It is one good running engine. As soon as I sent it back to him, I ordered my own.
I did a bench test of the JBA and compared it to the OS .55AX. Let me see if I can find those rpm figures. I didn't try that many props, just what I had handy. Fuel was Omega 10% castor blend. Temp was 65-70 deg. RPMs in thousands.
OS .55AX JBA .56
10-6 15.7 -
11.5 14.0 -
11-6 12.8 11-6APC 12.8 11-6MA
11.7 12.2 11-7APC 12.4
11-8 RevUp 11.3
I have never had a bit of trouble with the carb.
I tried the JBA muffler, a Tower .46 muffler and the OS .55 muffler on the JBA. The JBA stock muffler was 400 rpm faster that either of those.
The OS responds to a tuned muffler (Jett or Ultra Thrust) very well. 1700 rpm of the 11-6 and 1500 rpm of the 11-7. The OS is port timed better for tuning.
The JBA gets a moderate boost from a Jett. 11-6A 1000, 11-7A 1200, 11-6MA 700, 12-6MA 400. The JBA gets some boost, but not that much. It seems to be more sport timed. I did not feel the surge when the rpm hit the sweet spot like I did on the OS. The JBA, in my opinion, is a great buy if you don't mind a few tanks to break it in.
By the way, Turk is the real expert. When BigEd and I bought our engines, 3-4 years ago, Turk was telling everyone how to run them. He's been flying them for a long time. I only have 1 and several other types of engines so mine doesn't get used that much. He can tell you more about carbs and longevity.