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Jet Sizing


Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

Greetings,

I have a 2200 solid lifter Jab that I believe may need to have the main jet and or needle jet replaced. The EGT’s are between 1400 - 1500 degrees F (760 - 815 C) in cruise flight which makes me think this is running too lean. Spark plug inspections confirm this as they have turned from a brown in warmer weather to a very light tan now in winter. I removed the carburetor and the jets; main jet is a 255, needle jet is a 2.76.

Any suggestions on what size larger jets to enrich the mixture? According to the Bing tuning instructions attached, the main is used for climb and the needle for cruise. I don’t want to start randomly changing but I imagine anything larger will help.

It appears that the colder weather results in leaner mixtures. It makes sense since the air is denser and that means more air molecules to the same volume of fuel which reduces the fuel to air ratio. I didn't have EGT probes installed during the summer so the only comparison I can make is based on the color of the sparks plugs as mentioned before.

I had a Jab owner suggest the HACman mixture controller. He recommends to tune the carburetor on the rich side and then lean it using the controller as necessary until optimal EGT's are reached.

Thanks,

Alex R-


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

Hello Alex,

Just let me say now, here at Jabiru, we really don't like the HACman.  There is too much potential for things to go wrong.  I.e forget and on descent have a flame out or unintentional lean mixtures.

The first step in tuning the engine is to determine what needle the carburettor has.  The recommended one has a pronounced narrow tip (called jabiru economy).  With these needles we run 290 needle jet, a 235 main and a 45 idle.  

 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

@jabiru-support

Thanks. I’ll look to see what style needle was installed. This is the original Bing CV 94 carburetor Jabiru installed on this A2200 in 2001. 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

@jabiru-support

According to service bulletin JSB 018-2, my A2200, serial number 22A981 was manufactured before the introduction of the economy kit. Should I then consider the economy kit #4A172A0N?

 

This post was modified 3 weeks ago by Jabiruyank

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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

(@jabiruyank)

Well not the economy tuning kit as such, but definitely get the jabiru needle for your engine and the jets.  The result is that the mixture is able to run leanish to about 2900rpm and then it richens up.  I have a solid lifter engine with this combination (I have a 285 needle jet but it is quite warm here) and it is running very well.  Cruise egt is just over 710C at sea level.


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

@jabiru-support

Jabiru P/No. 4A131A0D-3, according to the bulletin? I assume I can get that in the US?


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

P/No. 4A138B0D-2   You should be able to get it.  If they don't have it they will just order it off us.

 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

Greetings Jab support,

Is there any value in drilling the idle circuit inlet aperture to 1.6mm? If so, is there a detailed procedure from Jabiru? Also, the print on JSB 018-2 references LLD at the aperture. What is that?

Thanks,

Alex R-

 

 


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

Hello Alex,

So JSB018 has been cancelled.  We don't drill them out anymore.  

So the answer is basicly no.  

I can't find LLD in JSB 018-2 so I can't help you there.  


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

Just curious on the LLD, no worries. Thanks for the answer on drilling, or not to!

Alex R-


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