Wrong spec carb jet...
 
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Wrong spec carb jetting for 3300

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(@aj_richo)
Active Member
Joined: 12 months ago
Posts: 15
Topic starter  

Hi Support,

My J230C has been flying with its second engine, a late Gen 3 - 33A2738 for some 414 hours. Since fitment the owners at the time reported high EGT's at full power on #2 and #6. Full monitoring was installed at the same time as the new engine. During the demo flight I went on it was noted #6 reaching over 720C on take-off, reducing rpm back to 2800 dropped the EGT back below 700C.

From what I can tell in the maintenance records no investigation into the high EGTs has been conducted apart from checking float levels and fuel pressure at the carb inlet. At cruise 2950 rpm ~2000Ft alt. #2 and #6 are hovering around 700C. The rest somewhat lower 680-690C.

I have recorded 75L/hr at the mech pump inlet with the electric pump on. 

I removed the carb bowl and checked the following:

Needle seat orifice 2.4mm

Needle Jet 2.76

Main Jet 275

I didn't disassemble the carb further to remove the needle, so I'm unsure what I've got there!

Compared to Table 5 - Carburettor Tuning in the current 3300 overhaul manual, it would appear the Needle Jet is a bit smaller than it should be, and the main jet is a bit larger. The main jet may have been increased to try and get a bit more fuel in, but there is no maintenance record. 

Would I be correct in suspecting the needle jet orifice is limiting the total amount of fuel available at full power?

Are there spare parts readily available to size the needle jet to spec and perhaps replace the float needle (it looked a little worn) ?

Cheers

Tony

This topic was modified 9 months ago by aj_richo

   
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(@jabiru-support)
Member Admin
Joined: 4 years ago
Posts: 181
 

Hello 

We have all the jets and float bowl valve parts.  

Our current jetting for a Gen 3 3300 is Needle - 2.85 or 2.90   Main - 2.60 or 2.55   Idle - 0.35

The needle should be a stepped one, the current part number is 4A139A0D.   


   
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