It's not you. The new batch of discovery engines that Horizon recently shipped out have something wrong with them. We ordered three for our shop and another shop on town ordered a few and they all have the same issue. I have personally ran these engines for a while now and they have been some of the best engines I have ever ran. Easy to tune, tons of power, 11-13min runtime, and great longevity. Until this last batch. All 5 engines are having the exact same problem. So I called Horizon because some of our customers want their money back. I know not many companies do warranty on nitro engines but there is something clearly wrong. All my old discoveries came with two shims. The new ones come with three. I've never had to seal an Orion engine before but I went ahead and tried it just to see if it fixes the problem with no luck. I set it up like my old ones with two shims and a Orion 6 plug same fuel same car one runs great still and the new one will not hold a tune or idle at all. Also I switched the carbs just thinking they had a bad run and my old one does the exact same thing. Horizon and Orion both do not want to help with the issue so we are supposed to just tell customers sorry about your luck???