I have an old kit built, manual start, Wren 54. The engine worked perfectly but was removed from a model a couple of years ago and wasn't used again until recently.

I have refitted the engine in another model and am now having problems with the start. The engine appears to flame out on start (but doesn't stop completely as it is still running on the gas) and then it ramps again. After a couple of these cycles it gets up to idle and is then perfect. I have had about 20 flights like this and in the air it is perfect. It just struggles to get through the start.

It was suggested to me today that it might be a dodgy pump (Hausl 280). I can't see the old trick of running fuel through it for a couple of hours helping as it has now had a couple of hours run time in the air. Is there anything else I can do to help 'free up' the pump or is it likely to be shot. I'm a bit wary of spending £120 on a new pump for this old engine, especially if it turns out to be something else.

Has anyone seen a similar problem during start that goes away once the engine is running?