Shut down Turbo and bang!

[Greg Vos]

Hi guys just reaching out to those with rotax exp, on two occasions recently I have shut my 912 down and the turbo makes a small poof sound ( 912 fitted with eveco turbo) almost as if I had not allowed it to cool down sufficiently.
The Wx in the Cape has been colder than normal and we are seeing temps around 9 degrees C, just adding this in case it’s relevant? Also I recently rebuilt the carbs and I am thinking possibly the idle mixture could be rich and it’s sucking in more fuel as it cools on idle?

It runs sweet and no power problems, at the coast we are boosting it to 39.5 inches and I have not seen or felt a performance issues, we let it cool down on idle rpm that I have set to 1900rpm.

Any advise will be appreciated

 

[wolfy]

Do you have egt readings on both sides, my first though was lean possibly.

wolfy

 

[Vance]

Hi guys just reaching out to those with rotax exp, on two occasions recently I have shut my 912 down and the turbo makes a small poof sound ( 912 fitted with eveco turbo) almost as if I had not allowed it to cool down sufficiently.
The Wx in the Cape has been colder than normal and we are seeing temps around 9 degrees C, just adding this in case it’s relevant? Also I recently rebuilt the carbs and I am thinking possibly the idle mixture could be rich and it’s sucking in more fuel as it cools on idle?

It runs sweet and no power problems, at the coast we are boosting it to 39.5 inches and I have not seen or felt a performance issues, we let it cool down on idle rpm that I have set to 1900rpm.

Any advise will be appreciated

Based on your description I would check for a sinking float Greg Vos.

 

[Greg Vos]

Based on your description I would check for a sinking float Greg Vos.

Vance the floats are fine weighed them during a recent service? I’m beginning to think it could be carbon build up in the turbo

 

[Rick E]

We have a lot of 914 rotaxes at our airfield and any backfiring on closedown seems to only happen when engines aren’t allowed to cool down correctly. I would imagine the same procedure should apply to all turbo configurations.
You might also want to check your fuel/air ratio at the exhaust.

 

[Smack]

Greg, I'm going to suggest "excess fuel or fuel blow-by that is not burned in the engine, but ignites in the hot turbo section". Perhaps as the engine RPM is winding down, there is still fuel being pulled out of the carburetor, passing through the cylinders, and igniting in the turbo.
Brian