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Carb jetting.

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Carb jetting.

Postby Dave Mickelson » Wed May 23, 2018 8:41 pm

Newby here. Just bought J250SP. Runs great, flies great. I am wondering if I am too lean in cruise flight. Egts push 1400. Stock jetting as far as I know. Has anyone went to needle jet?
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Re: Carb jetting.

Postby diablo » Thu May 24, 2018 8:48 am

Hello Dave and welcome ...

Converting 1400F I get 760C. Depending on RPM, that seems that is spot on in my book. Here is an extract from the Jabiru specs table that shows appropriate EGT’s for the Jabiru engine.

Table 3.

Target EGT Readings

Power Range EGT Reading
Mid-Range/Cruise 680 – 750°C (1256 – 1382°F )
Above 70% Power 640 – 680°C (1184 – 1256°F)

Most importantly is the EGT spread across all cylinders that you are getting (if you are monitoring all EGTs). If they are pretty close, I would not touch a thing and fly happily.
Sent from my "Electronic Numerical Integrator And Calculator" E-N-I-A-C
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Re: Carb jetting.

Postby Dave Mickelson » Thu May 24, 2018 7:47 pm

Thanks. It looks to be close to target temps. CHT looks fine. EGT cools down with full power as mentioned in Jabiru service bulletin. I will keep an eye on them.
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Re: Carb jetting.

Postby diablo » Wed May 30, 2018 10:45 am

If you are getting constantly higher EGTs than expected, check system for leaks (inlet rubbers can crack and plenum mating hoses have been known to come loose). I would also check exhaust bolts are tight as they seem to work their way loose. Use 1/4" nordlocks to ensure that they stay on tight!

Depending on the size of your main jet on carb, you go one size up to richen mixture slightly.
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Re: Carb jetting.

Postby Dave Mickelson » Thu May 31, 2018 11:09 pm

I installed 2.90 needle jet and a 260 main jet. Much better.
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