The lean running thing

[ianboag]

Confusion reigns.

 

My J200 has the economy kit fitted. I cruise it at 100-105 knots - it's appreciably quieter than 120 knots and I'm comfortable flying like that. I have a fuel flow meter.

 

At 100-105 knots I burn about 15-18 lph. On takeoff the meter says about 33 lph and a 120 kt cruise uses about 25 lph. Both quite believable figures.

 

At the 100-105 cruise the EGT is typically around 275 F (I have an early "thick-fin" engine). The oil temp sits on about 80 C - I have the Aero Classics oil cooler half blanked off with tape. An extended WOT climb takes the CHT to 325 and the oil temp to 100. The EGT looks like low 700's C.

 

There are no problems with oil pressure except for the rather strange (to me) observation that the oil pressure increases as the oil warms up. This is the opposite of what I would expect but since it's comfortably in the green at all times I don't stay awake about it.

 

I did a couple of X-countries last week and in 5 hrs flying (which included six takeoffs) lowered the oil level from midway between the marks to just above the low mark. That didn't seem excessive to me.

 

The engine has done about 250 hrs. At 200 hrs I found excessive blowby in #6 after a leakdown, so I honed the pot and put in new rings then gave it 30-odd hours on running-in oil after that. I haven't done a leakdown since, but the low oil consumption suggests there isn't an obvious problem.

 

I read JSB-018 and ended up confused. Am I running things too lean?

 

All opinions welcomed.

 

Cheers IB

 

 

[Yenn]

I don't think you are running too lean. You have the temps sorted out and the blowby was fixed by honing the bore so I doubt that it was caused by lean mix.

 

I would expect a lean mix to give high CHT and EGT when using a high power setting, such as on climb out. If it was excessively lean there would be piston and cylinder head damage including to the valves. there is little fear of damage caused by too lean a mix when you are using a low power setting as you do in cruise.

 

 

[Guest brentc]

From what you have described you have the NEW economy kit versus the OLD one. The old economy kit was around 20-21 litres at 2,800rpm.

 

The original carby was around 27 lph at 2,800 rpm.

 

The NEW one, sits between at possibly around 23-25lph.

 

Your figures sound like the current configuration as specified by Jabiru.

 

 

[Captain]

At 100-105 knots I burn about 15-18 lph.

A 120 kt cruise uses about 25 lph.

Ian

 

What revs are you using at each of those speeds and fuel burns?

 

Once I know that I can relate them to my 230.

 

Regards Geoff

 

 

[jetjr]

Brent - my J200 has original taper needle (new economy kit still in the shed) and it uses 24 lph @ 2800rpm???

 

You can tell its lean on take off - gets high CHT and EGT but OK after this

 

JR

 

 

[jabpilot]

As a newbie to this site, my two bits worth may be a little late - but...

 

The economy kit was introduced originally as a request from Mossad (Israeli secret service) who operate Jabiru engines in their spy planes. They wanted even better economy as their aircraft loaded with snooping gear & fuel had to stay airborne for days at a time. As there is only so much fuel you can carry, even more fuel economy extremes were demanded.

 

Enter the original fuel economy kit.

 

According to Jabiru there were two training planes that developed problems caused by too lean a mixture with the original economy kit fitted. Due to the harsh treatment training aircraft often get, (ie. sitting on the deck, motor running on hot days with bugger all airflow over the motor while the instructor yaks to the student then immediately followed by steep climbouts, etc) a modification the economy kit was introduced. Most of us operating our own Jabs will not be subjecting our baby to this treatment. However, Jabiru must cater for the worst case scenario. In other words, the official line is to have the modification to the economy kit done. Jabiru were offering to assist in this process for free if you flew up to Bundy. Of course, this has already been performed on new motors.

 

Ultimately, the choice to have the mod to the economy kit done is that of the owner.

 

 

[Guest brentc]

According to Jabiru there were two training planes that developed problems caused by too lean a mixture with the original economy kit fitted.

By golly you just made me laugh out loud!

 

2 aircraft with problems?

 

Try 200 !!!!!!!!

 

The 2 aircraft you are referring to are the 2 x Leaseair J160's that were operating out of Bankstown. Either one or both of these had engine failures within the same week due to overheating in really hot weather. It was put down to '45 minutes of taxi time' which we all found hard to believe at the time. As a result, their mixture got richened up and the under-cowl duct was developed to help pull the air through past the oil cooler and to increase head cooling.

 

I note that both of these aircraft were GA registered and had a much higher profile due to where they were being used, versus their RA-Aus registered counterparts. Makes you wonder a little.

 

 

[jabpilot]

Perhaps I should have added after '2 training planes' the words "when they told me"

 

I guess you can only glean so much sitting in the Jabiru staff room!

 

 

[Jabiru Phil]

There are no problems with oil pressure except for the rather strange (to me) observation that the oil pressure increases as the oil warms up. This is the opposite of what I would expect but since it's comfortably in the green at all times I don't stay awake about it.

 

Try tapping the oil pressure gauge. I reckon you will find that it indicates a "sticky gauge"

 

My experience,

 

Phil:thumb_up:

 

 

[kevinfrost]

Yenn, I've found that if the mixture is too lean the EGT is most likely higher around the cruise mark. On climb the CHT normally comes up but the EGT comes down due to the cooling effect of the increased fuel flow. That's the experience I've had in the past.

 

 

[jetjr]

Yep, but the original carb setup ran lean at WOT

 

JR