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Engine RPM loss at WOT on climb out (taking off) - scary!,

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New Member
Joined: 6 years ago
Posts: 1
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Hoping someone can help me with tricky issue I have with my Bantam powered by a Jabaru 2200. It appears only when after I do an oil and filter change that when taking off, I apply fullpower down the runway - everything good but as I reach about 200ft the engine losses power. It doesn’t surge or miss, so much as shudders and starts running really rough and drops power to about 2000 RPM ( from 3000RPM). Quite scary as I’m taking off from a short strip (with trees all around) and it does not want to climb out to well at 2000RPM. It then regains fullpower for a moment and drops it again. I’ve replaced everything electrical (I’m a mechanic by trade), have done all the engine tests - engine seems to be healthy - and I’ve come to the conclusion it is the fuel not vaporising properly caused by too much oil in the sump and the fuel not heating up sufficiently in the plenum chamber to ignite the fuel mix properly in the engine. I only ever put 2 litres of aero shell W100 in the engine when I change the oil. I know this is a long rave, but its got me a bit beat. If anyone has similar issues or if Doug could give me his thoughts I would love to hear from you. Cheers, Johno.

Member Admin
Joined: 6 years ago
Posts: 82

Hi Johno,

That is a weird one.  Does it do the same thing if you do an engine run on the ground?  Is it a hydraulic lifter engine or solid lifter?

I know some vision aircraft in colder climates run a cowling over the sump to keep the oil and plenum a bit warm, but I'd only expect that in pretty cold weather, and even then it's unusual for them to run lean enough to miss or run rough - that's usually a sign that the engine is a bit rich.  Does the engine have carby heat at all?



New Member
Joined: 5 years ago
Posts: 2



I had similar issue with my 3300. Added airflow of takeoff had "stumbling". If I reduced throttle, smoothed out but WOT continued to stumble. 

Mine was fuel starvation. I noted when turning on electric boost, no issues. Mine was a new build so the float bowl appeared to have a restriction preventing the carb from keeping up with the takeoff demand. I removed float bowl and cleaned fuel passages and valve. Verified float setting. 

Resolved my stumbling issue. Hopefully helpful. Stumbling on takeoff is an exciting event!



New Member
Joined: 3 years ago
Posts: 1



Hi Tony. In know this is a few years old but Just was wondering if you figure out what the issue was. I had the same thing happen to me yesterday afternoon. 

Member Admin
Joined: 4 years ago
Posts: 199

Hello @wood,

The usual reason for this is fuel starvation.  The first thing to do is check the fuel flow rate to the carburettor.  Also do you have the electric boost pump turned on when this happens?

Another thing you can do, if you have a nice big airfield, is to do a take off with a fuel pressure gauge in the line between the mechanical fuel pump and the carburettor.  This can show if fuel pumps aren't keeping up, when the pressure drops to zero.


Active Member
Joined: 5 years ago
Posts: 3

Hi Johno and others

Stumbled upon Johno's original post. Just wondering if you resolved the issue?

I am flying a  very early J160 built in 2004 (s/n 005) with same vintage 2200 engine. I bought the plane in 2019 after it had been not flying for many years. It was brought back to life and I was happily flying (about 580 hrs on plane and engine at the time) when something similar happened. Airfield at 200 ft MSL.  Climbing after start, at 500 ft AGL the engine RPM drops to about 2300. I can still climb, but slowly. At circuit altitude (1200 ft) back to normal. Everything checks ok, mags, fuel pressure etc.

This repeats about every two starts. Only starting from this elevation. Started from another field 1000 ft higher, no  problem. Climbing at higher altitudes, 1000 - 3500 no problem. Tried with/without carb heating no difference. All spark plugs look fine. Oil is fine. Compression fine. Switch magnets no difference. Mystery.

Now have not flown the machine for 2 years on account of another problem, now resolved. In the meantime I have renovated every aspect I can, complete overhaul of fuel system including both fuel pumps and all carb rubber parts. One fault I found was the fuel lines, peculiar routing, now rectified. However that does not explain why the problem suddenly occurred at flight time of over 500 hours.

It will be very interesting to start flying again.