Hey Guy's! I have not had a chance to read back on all the details. Out of the blue, RCU started to contact me again on the posts to this forum, so I have been out of touch.

If it has not been mentioned already, the knocking sound can be caused by high nitro content. So many people believe that if an engine runs well on 5% it will run better on 10% and even better on 15%. This is not the case. Nitro acts like moving the distributor on your 1969 muscle car. The more nitro, the more you advance the ignition timing. If a prop is too small, or you have too high a nitro content, you will get pre-ignition. The .76, which is an awesome engine, by the way, was designed around 5-10% nitro. If you are at the upper end of the propellor range, 10% will work fine. When these engines are manufactured, they are done so within certain tolerances. This is why you can have two engines that apear identicle, but have different characteristics. Wayne's engine that knocks, likely has tolerances built in that mechanically have the timing advanced further than the other engine. If this is true, lowering the nitro content will likely reduce or eliminate the knock, lengthen the life of the engine and improve overall performance. These differences can often be adjusted by machining the cylinder and head combination. There is facinating information on this, on the MECOA website. How the cylinder and head come together is refered to as "squish band". I have a K&B 1.00 that ran awful. You could fry an egg on the muffler, no fooling! When I measured the squshband, I found that the band was so large, I had ignition delayed to the point that it took place in the muffler. It was so far out of tolerance that I could not adjust this with nitro content. I had a few thousandths machined off of the top of the cylinder, and now it runs beautifully on 10% nitro. In your case, I suspect the squish band may be the opposite of what my K&B was. It is likely very tight, so ignition is happening way too early. I doubt it is so far off that nitro content won't solve the issue.

Andy