Greetings fellas from a stormy S.W.France.

Can any of our colleagues explain the following please .....

Went flying Saturday morning. Very little wind , nice ambient temp' and an empty flying field. It was Saturday morning !

Fired up my Magnum 36. Set up was an APC 10.5x4.5 prop' , a 'standard' muffler from an Evo 36 , and some new fuel with 20% lube' in total .....50% castor, 50% Klotz and 5% nitro.

The Magnum is normally dead reliable. This was a new fuel brew from a reliable source.

She would get to around 9,800 rpm then 'jump' to 10,500 as I was trying to set the needle to the new fuel brew. I couldn't get her to hold 10,100 approx' which is my launch rpm on this 'plane.

I switched to some typical 'RC' fuel I had with me. This had again 20% total lube , BUT was around 17% synthetic and 3% castor [ the castor was added by me ] and again 5% nitro.

The Magnum was fine and dandy. Set the needle at around 10,100 on my old tach' and off we went. She held the setting without a murmer.

So guys , is it 'true' you can have too much Castor in fuel ?
Maybe ABC type engines prefer more synthetic brews ?

As an aside , I also flew a 'plane with a TT36 on board using the first fuel  mentioned above [ the synthetic/klotz mix ].
This engine loved the castor/klotz mix.

The TT36 however had a tongue muffler with extra holes .
I was using a TT 11X4.5 prop' and launching at 9,100.

Maybe there is a correlation between a 'restictive' muffler versus a freer flowing more 'open' tongue muffler.
The Magnum having a 'restictive' muffler and the TT36 a free flowing one.

Did the Magnum with the 'restictive' muffler dislike the heavy castor fuel  ?

One for the engineers maybe ,

Any contributions much obliged ,

Regards ,

Robin [ we-pat Brit' in the Charente full of ex-pat Brits' ]