This refers to my earlier post where I had similar problems with a 55ax.

I have a 75ax in a Reactor 46 with a 14x8 prop. I am running klotz 100 (synthetic-castor 80-20 blend) with 10% nitro (basically, 1 bottle of the klotz which is about a litre mixed with 3.5l of methanol and 500ml of nitro). The engine in question was out of use for quite some time, its been run-in and then washed in plain alcohol and thoroughly oiled before it was put into storage and runs fine otherwise. Am using a 240cc generic make tank with a single normal clunk and 3 line system. Using Dubro regular tubing which I have pressure tested beforehand to eliminate tank problems. The manual recommends 2-2.5 turns for the HSN and 1.5 turns for the LSN as rich for starting.

Couple of weeks back I started with the 14x6 with the needle 3 turns out for the HSN and 1.7 turns for the LSN. The idle was quite OK, I left it there. I found that the peak RPM was about 2.5 turns of HSN so I set it about 2.8 turns for the HSN. When flying without cowl I didnt experience too many problems but I did very little hovering, mostly pattern at that time

Didnt fly last week

This week on Saturday after refitting the cowl, I noticed it lost power in vertical every time I tried to hover. Ultimately I had a deadstick and had a hairy-scary landing but no damage.

Though the cowl has a lot of cooling holes (both inlet and exit), I decided to fly without cowl anyway today. I tuned the engine with a colleague holding it vertical (I couldnt do that yesterday) and it tuned at 3.2-3.3 turns out. Again, I lot a bit of power in vertical but it didnt deadstick and I did the 10min flight. Someone suggested to give it a tank of run-in on the ground just in case. When doing that I went in and out with the HSN from upto 4 to 2.8 turns. After a couple of minutes at full throttle when I idled, she cut. I immediately noticed that there was no compression (or very soft compression). We realised the thing was very hot, you could feel the radiant heat sitting in front of the model even though there was a good breeze and it was too hot even to touch. Interestingly, I had exactly the same problem with the 55ax. I didnt have the instrumentation to measure the temperature today

Do you think that 10% is too much nitro? My colleague is flying with 4% nitro and his airplane flies OK but his batch was finished, so I couldnt test it today. This was actually my 4c mix which I am using on all my engines. Outside conditions are at about 38 Deg C so its very hot to begin with

Point is, I have about a litre of fuel left in this batch. The next batch I can drop the nitro content. Or I can brew a fresh batch with no nitro and add in this remaining fuel which will give me about 2% nitro effectively. Alternatively, I can brew a whole seperate batch with about 2-4% nitro so as to elminate all problems. Please suggest

Ameya