I have a magnum 70 four stroke on my phoenix models sukhoi. Both are brand new. The engine seems like it misses at the hi rpm setting. This is the first 4 stroke for me. i have been running 15 percent 2 stroke glow fuel. Is this the problem? I mounted the engine at a 45 down angle but have now since moved it to a horizontal mounting (used to that with the 2 strokes) Still have the same issues.