Sonex 759 update

[Corby202]

Coming up to 10hrs now and about 25 landings. I had a few issues to sort out. The first one was the engine was running very rich, I didn't figure it out straight away as it was running rich because of to much air. What was happening was the naca duct feeding air to the carburetter was pressurising the mixer box to much and the altitude compensating pipe on the Bing carby was putting to much fuel into the carby.I redesigned the mixer box lid and fitted some bleed holes into the box, to save wasting this cool air I took hoses off the help cool the RDAC unit and voltage regulator. The starter motor clutch occasionally would spin without turning the engine over so Jabiru sent me a new one which seems fine.
The MGL unit now and again showed some erratic oil pressure readings so I separated the oil sensor wire from all the other wires and it seems to have fixed it.
The plane itself I am liking more every time I fly it, I think it is a very confidence inspiring plane to fly, it handles the rough air better then I am used to, the same with the moderate cross winds.
There was a young photographer taking pictures yesterday at the airfield, I think these look very good.
https://www.flickr.com/photos/78427482@ ... otostream/

[Bryan Cotton]

Some great shots there Phil!

[Corby202]

Thanks Bryan, I know very little about cameras but I suspect a good camera and a steady hand is required to get that sort of quality. I had to look twice at how much the bottom fuselage skin concaves when its in the air. Think I will also have to clean the bottom of the plane.

[sonex892.]

The first one was the engine was running very rich, I didn't figure it out straight away as it was running rich because of to much air. What was happening was the naca duct feeding air to the carburetter was pressurising the mixer box to much and the altitude compensating pipe on the Bing carby was putting to much fuel into the carby.I redesigned the mixer box lid and fitted some bleed holes into the box

This is interesting Phil. I did the same as the jabiru airbox's and put a rubber flap on my airbox to avoid this. It now has me wondering if this flap is open and dumping unfiltered air all the time. I'll try and figure out a way check it.

I just had a look at your build log and couldn't see what you did to get air from the airbox to the carby. Do you have any photos? Many years ago I initially had a similar over rich problem on my Jab powered Sonerai, it was scat tubing from airbox to the carb that was the culprit on it.
Steve
Sonex 892

[Corby202]

I am away for a few days Steve but I will take some pictures of the new air box lid when I return. Its very similar to a standard Jabiru lid. I had some spare thermocouple leads so for a test I put one at the back of the engine bay and one near one of the air box outlets near the voltage regulator. The difference in the air temp makes me think it was worthwhile not wasting that cool air.