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Jabiru Engine Tuning JSB018-2

ross holz

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Got some interesting results today. Put an Oxygen sensor on exhaust of my recently acquired J200 to check mixture. Results are as follows


-idle and full revs fully rich on gauge


-between 2200 rpm and 2800 almost fully lean on gauge


-around 2000 mixture was optimal on gauge (didnt go much lower in revs whilst flying)


These results were using the jets and needle recommended in JSB018-02 ie 285 needle and 255 main jet etc.


Then put original jets and needle back in Bing carby and got


-idle and full revs fully rich on gauge


-2000 to 3000 mid scale rich on gauge


Also interesting with original jets, 280 needle and 280 main and original needle set second grove from bottom got 2850 static rpm but could only get 2600 static rpm with JSB018-2 recommended jets etc.


Whilst looking for a jab to buy a month or so ago someone else said they ran lean with new jets which made me wary to start with and thought it needed checking.


Just for comparison


-running with 60" diam 53" pitch prop.


-using premium unleaded (lead will clog up oxy sensor if your using avgas).


-have egt on order so cant give that but cht and oil temps look good and even on the low side for both old and new jet combinations


-engine showed signs of over heating. Had snow white plugs when running on avgas and exhaust gaskets and washers under screws were burnt out. Tappets and head torques needed adjusting after approx 30hrs running on JSB018-2 jets.


Main problem, on my motor at least, seems to be the new needle. I can see why jabiru recommend working the engine hard as that was the only time the new needle supplied enough fuel (for my motor and maybe others)


This is just a heads up as it may not be the case with other jab engines.



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If you read this JSB closely youll see theres a separate set of jets for solid lifter engine (which J200 came with) also it mentions you may need to use bigger needle jet to richen things up.


Your engine most liekly has "thick finned" heads which do run a fair bit hotter


First thing Id do is get 6 x CHT and 6x EGT before you fiddle too much more


In saying that my J200 ran way better on old original jets too. new jets were primarily to reduce fuel use. Ive now running a size up on both jets and still have one hot EGT cylinder.


Look very closely at fuel level in bowl too, it stuffs everything up if it gets low on high RPM, there was a few which had issues at WOT where float needle and seat was too small but really you'd only see this at WOT



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I agree whole heartedly with jetjr that what you need now is 6 CHT & EGTs.


Trouble with any "mixed gas" exhaust analyzer is that it only tells you what the final mixed output gas is doing. The jab engines however are well known to have spreads where some cylinders can be lean and some rich - the final average is what you read in the common exhaust. It may turn out to be a reasonable reflection of what is going on but it might also give a false sense of security.


Changing the needles first may be a complex exercise that you just have to repeat later once you get all cylinders monitored.



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For anyone whose interested I used an oxygen sensor from car wreckers $20 and fuel/air ratio gauge from cash converters $30. Tried gauge on car and seems to work ok as car computer kept gauge in optimum range and rich on acceleration. Oxygen sensor wire colours are shown on internet for various brands. Some have heaters to make them start reading sooner. Hardest part is installing gauge in panel.


It may not be the traditional way of doing things but help give an understanding of what the jab motor is doing. Id rather run rich than lean any day.


Hopefully with the aid of egt gauge on order I can run at something less than flat out whilst flying and enjoy the scenery or get better economy.


Saw in a catalog from usa that they are commercially available for sports aircraft but you need to replace sensor every 200 hrs running on avgas.


Might look for a switch to flick through cylinder egts as its hard to justify spending thousands on flash dyson glass panels etc.



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I saw a fairly nice temp gauge instrument on JabSP6's jabiru last Saturday. It is a stand alone 3 1/2 inch round gauge plus 6 CHT & 6 EGT sensors. I think it was something like "MGL" Industries or something like that. He said it cost about a $1000.


It always seems hard to justify the costs till the costs of NOT doing it kicks in. :-(



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Yep they are expensive but you've got a $15K engine there, the MGL unit looks good value


Dont waste money on single guage and multiple probes


Cheap instruments are fine for reading things which arent important


If you are playing with fuel mixtures and jets its critical you see whats happening at EVERY cylinder, it isnt like an car engine where water cooling evens temps out.


Those Dynon type units are good value for what they give you in information and alarms.


Too rich will see increased cylinder wear (massively so) and fouled plugs let alone extra fuel



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The 6 x EGT/ 6 x CHT Gauge and sensor Jaba-who is refering to is MGL's TC-3 (12 channel thermocouple system) and probe package.


From memory it was around $1200 but don't quote me on that. It was about 18 months ago worth every penny compaired to a new engine


I bought it from Bernard atAsia Pacific Light Flying Pty Limited


(02) 6259 2002


Mobile/Cell: 0419 423 286


E-mail: [email protected]


Web site: http://www.lightflying.com.au/



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