Fuel usage

[AndyB]

I have asked this question on a number of forums and still got no solution....

My AC Nitro always used 4.25 l/hr with trims in. It recently had the pop-off needle fail and starting using lots of fuel. When measured I found it lifted at 14 psi, but then did not re-seat and just kept passing fuel. I re-built the carb and fitted a new pop-off jet. I used the old spring as the pop-off pressure was spot on at 14 psi. After re-build it ran quite well, except it bogs down in the mid range. It also now runs on 2.7 //hr. I have done a number of flights and always the same really low fuel usage. Both H and L jets were initially set to one turn out.

The bogging down is like this. If I let the rpm drop below 5000 for more than 10 seconds, then press the throttle quickly, it will stall. If I press the throttle really, really slowly, then it will pick up again. If I let it drop to idle, then hit full throttle, it will work.

To try and cure the bogging down I have tried. Low jet in 1/16th of a turn, no difference. Low jet out 1/16th of a turn, no difference.

Before the carb re-build my plug always looked a little black. Now the plug looks perfect brown with no black. Max rpm is exactly where it always was before re-build at 7160 rpm....although AC tell me it should be nearer 7600 with the new e-prop.

Any thoughts? 

[Bob27]

From what you are saying, the low jet still sounds way too lean. You will likely need a lot more than 1/16 of a turn.

Anyway, if I were you. I would check engine temperatures. If the engine is still running in a reasonable range, I would figure out what you did and patent it. Lol

[AndyB]

Hi, I fitted a CHT gauge last week as I was bothered about what is going on. Max temp is 230 C....when I run full throttle for over 2 minutes. At take-off I only get to 220 C (less than 30 seconds at full). At cruise throttle it is 185 C.