Engine runs at idle for a few minutes then gets rough and dies. Have to pull a few times to start. Seems to run at high revs OK (a bit noisy to test). Cleaned out carb thoroughly and it seems the two mixture screws "H"and "L" are very sensitive and affect one another and the performance considerably. Cannot get the engine to idle for more than a minute or so. Can anyone please tell me if there is anything more i can check on the carb and how to tune it properly. Yhank you, Keith Moir