Going on a Diet

…or “Watching My Carb Intake”

I was going to call this “Oil’s well that ends well”, having finished rectification of the oil leak…but it didn’t end well.

There was a bit of faltering in the engine during the ground run to check for leaks, almost as if the mixture was running too rich – too much fuel starving the fuel air mixture of air.

After shut down we found fuel dripping from the air filter box under the carburettor. Time to get the tools out again.

Disconnecting the air box revealed the carb intake:

…and I lay under the aircraft with the fuel controls at different settings to see what would happen. There was a persistent drip of fuel from the “float bowl atmospheric vent”, which as the name suggests, should probably be filled with air rather than fuel. This fuel would be getting into the carb throat and richening the mixture. We decided to remove the carb completely and investigate further.

The fuel lines and control rods were disconnected and the carb removed. Note the use of tie wraps to annotate which control rod is which, red for mixture, white for throttle. It should be impossible to connect them up wrongly, but where there’s an idiot, there’s a way. The nuts are rethreaded onto the bolt threads for the same reason, to stop them getting lost.

Tie wraps are wonderful things. Taking the carb off involved several different sizes of spanner, and it would be nice to have them easily to hand when it is time to reassemble, so I tied them together rather than throwing them back in the tool box:

…and also took some notes as to which spanners are used where:

Once the carb was off I decided to send it off for an overhaul so that the experts could rectify the problem. It had done 1800 hours and was probably due for one anyway, and getting it done professionally gives added peace of mind. Here it is just after removal:

And here it is ready to dispatch. I chose Nicholson McLaren to do the work because they have a good reputation and they were the most “economic” quote! They featured in a video by Jon Hunt, see:

“The Flying Reporter”

Lots of great videos on his site

Just a week later and it’s back, freshly overhauled and beautifully packaged. It’s lovely and shiny, almost looks new…

It arrived back just in time for my return to work. Typical. Luckily all was not lost…there was a bit of preparation required, so I did that at work, in between flying…and who says men can’t multitask?

Next week, refitting and ground run to set up the idle mixture. Sandy the inspector is helping with that one. Sooner him than me crawling around under a running engine fiddling with an adjustment nut right next to hot exhausts.

If all goes well, it’s back into the air. Can’t wait…