I bought an GTX rfi with a wiring problem which now have sorted. Now the motor runs for 1 or 2 seconds and cuts out with a huge backfire loud from both manifold and exhaust. After investigating I found the rotary valve shaft got a free play 1/4 -1/2 of an inch (approx 5-6mm movement). Is this normal or could be this cause not start symptoms. Got 155 psi compression on both cylinders. Also got good spark and fuel in each cylinders.