A friend is flying a pattern ship with a Saito 150 on the front. Until a few weeks back everything was fine. The flight was easily completed and with a totally reliable engine. Unfortunately the engine appears to have gotten wind of the upcoming UK nationals in which he is competing. The engine now cuts without fail every flight, to the extent that he is now afraid to fly the plane for fear of doing serious damage.

The symptoms are as follows. Take off and fly the circuit on about half throttle. Reducing the throttle to idle and then attempting an increase of the throttle setting causes the engine to cut. This is with the plane in a level circuit. It will also cut when throttling up after a loop or similar. The problem has us stumped really. Initially the problem could be replicated on the ground by nosing down the plane for the duration of a downline and then throttling up. Richening the low speed needle has cured this, to the extent that it will run perfectly on the ground for a whole tank of fuel.

The setup is as follows:

Saito 150
Baffled 4-Stroke Pipe Exhaust
Coolpower 15%
OS 'F'
APC 16x8
Soft Mounted
Running 8800rpm on top end, 2800rpm idle.
Tank is inline with carb and is 16oz.

We have: replaced Glow Plug, replaced Fuel line, added a header tank, tightened engine mounts, fiddled with needles. Settings are now approx 2.25turns open on the high speed, low speed needle setting unkown, but just out from flush IIRC.

Three of us have been working on this, but we're stumped He's got some CP30 for competition use, and I'm tempted to try that next and see what effect it has.

Any ideas guys please? The Nationals are three weeks away today, and he's getting kinda worried now.

Cheers


Chris