Ron,
Thank you for your suggestions which are greatly appreciated. I have been
working
on the Europa today checking a number of the things you suggested.
I found all cables to be in good condition and the physical operation of the
carbs
appears to be correct and in sync. I have yet to re balance, but I will explain
why later.
The carb bowl vents appear to be Ok and plumbed in and connected correctly.
Switching mags makes no difference to the noise.
The blades have been checked, are all at the same pitch and are within the
manufacturers
limits. A basic check of the tracking has been conducted and no problems
highlighted. The blades have not been dynamically balanced.
I can find no damage to the engine mount, or mounting bolts which are torqued
correctly.
The aircraft was converted to a Tri Gear in 2007 which mod are you
referring to?
The chokes are closing correctly, there is no leak in the balancing tube and the
plugs were replaced last September.
The spinner is in good condition and on tight, with all screws checked and hub
appears to be fine. No changes have been made to any part of the prop system.
I do not often use 100LL only 40 litres in 33 hours. The total engine time is
265 hours and as far as I know the gearbox has never been removed or checked.
I have checked the slipper clutch friction torque and it was 24 ft lb well
within
the range stated by Rotax. I never have any starting problems.
When I was checking the slipper clutch I removed the four upper spark plugs. I
was surprised to find those from cyls 2 and 4 were very black and sooty but 1
and 3 were perfect. I checked the needle jet in the left carburettor and found
the circlip located on the richest setting. I moved this down one notch,
re-assembled
the carburettor and test flew the aircraft. For nearly one hour it was
perfect with no vibration at any cruise setting from 28 inches to 25 inches
MFP, but after descending into the circuit and returning to cruise power the
vibration/harmonic
was very noticeable at 26 inches MFP. Obviously I need to re-balance
the carbs and I will do this tomorrow, but it does seem that working
on the carburettors/air intake system seems to improve things for up to 60 mins
and then the problem returns.
Regards
--------
Gordon Grant
G-BWFH
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