Just checking im getting this right.

Have a Hyper 7 with Collari SX2200 engine. Started it for first time yesterday. Engine was quick to start up but after a couple of minutes, it would rev up and down, like pulsing the throttle. There was no movement of the throttle servo or carb so it has to be to do with the engine itself. The engine would also cut out about 4 seconds after removing glow starter.

My guess so far is an air leak. Stripped it down and noticed one of the 6 screws holding the head was missing so replaced it but havent had chance to test again yet. It also had 2 head shimms fitted which seemed to be giving it quite a lot of clearance.

Last problem was oil around the engine but i've put this down to the exhaust manifold not sitting right and leaking from the manifold seal.

Am i going down a logical path or am i missing another potential cause to the revving.