engine flooded after leak down test

All I can think of is a problem with the fuel pump diaphram. The leakdown test naturally pressurises the crankcase and therefore the back of the fuel pump. If there was a split in the diaphram then the pressure would force any fuel in the lines into the carbs and possibly overcome the float value forcing the level to rise and fuel to flood the venturi via the main jet.

Let us know what you find, it's an interesting one.

This is an odd one. I've never seen this. Seems like air pressure would have the opposite affect. Plus if it forced fuel into the cylinders because of an issue then why didn't it get forced into the oil. I can't see how the compression test would do this. I would run the engine for a while and then do another compression check and see if it does it again

Maybe Rotax can chime in here. 

One thing I would advise anyone. If your not flying turn off the fuel and it's even more important for high wings.

"I was forced to remove the spark plugs and rotate the shaft with the starter motor for around 5-10s to clear. Puffs of fuel were visible from the spark plug holes. After this operation the engine started."

This may not have been caused by the compression test. Plus when you rotated the engine with the switches you activated the mechanical pump and it would put fuel into the cylinder.

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Thanks. i'll check this. At the date fuel pressure is in normal range and there was no leak from vent hole

my only guess at the moment is that when I did the leak test (I'm no expert) for the first 2-3 attempts I couldn't identify the exact TDC and therefore the propeller rotated a lot.

so it may have happened that this opened an inlet valve and pressurized air enters the manifold.

from that condition (and 6 bar are a good pressure) an effect can be derived like a air powered vacuum cleaner (venturi effect)  that sucks up petrol in the cilinder in test or other with an open inlet valve.

 just a hypothesis..

"my only guess at the moment is that when I did the leak test (I'm no expert) for the first 2-3 attempts I couldn't identify the exact TDC and therefore the propeller rotated a lot."

The propeller should be restrained, from turning, by either an assistant or some other way eg strap/rope

TDC can easily be identified:

One spark plug from each cylinder removed.

Finger/thumb over spark plug hole

Rotate engine (in normal direction), using prop, slowly until you feel pressure/compression on finger - this is the compression stroke for that cylinder

Insert, into cylinder/sparkplug hole, a plastic/wood rod of sufficient length to touch surface of piston (a metal rod eg screw driver, can be used but potential for damage higher)

Take care not to jam rod in cylinder - best to hold/feed clear of sparkplug thread

Continue to rotate engine slowly. Watch rod. When rod stops moving piston at just before TDC.

Mark rod

Continue to rotate engine until rod just starts to descend. This is just after TDC.

Mark rod

Remove rod - mark half way between the two marks

Return rod to spark plug hole, reverse engine rotation to half way mark - this is TDC