Jabi running rough

[Neophron]

Hi guys!
A friend and I just finished building his new Skyranger Swift with a Jabiru 2200 (85Hp) engine. The Jabi started first time and pured like a kitten over a bowl of milk during the ground testing. Even on her maiden she performed beautifully, but around her third hour she started running rough after take of while doing touch and go's....He did a mag check and the right mag dropped more than double the allowed rpm. She was grounded and given some TLC... all wiring checked, carb inspected, could it be carb icing... no carb heat was used... could it be a bad spark plug and why are the spark plugs so black, so change the plugs... Started her again and their she was back puring with no problems! Took her flying for 35 minutes no problem! Later it was time for another flight and the problem popped out again... on the ground this time while doing the mag checks. When the left mag is switched of the engine runs very rough with hi rpm drop....? First right now left? Could the engine be running to rich and fouling up the plugs? From time to time while on the ground you can see smoke coming out the exhaust, not much but visible smoke. Is this normal? He is running her on 95UL. All temperatures and pressures perfectly in the green. We are a bit lost here ... any thoughts ?

[janpetcc]

what fuel are you using

[janpetcc]

used jabi on mogas she runs rough then fouls plugs. not the case using avgas. think you must adjust the carb for the lower octain.

Jannie

[Neophron]

Thanks for the reply so far.
Don't want to sound dumb, but how do I adjust the carb for the lower octain.

[Rudix]

I run my Jabi on 95 without any problems (270 hours so far). The only problem you could have with 95 is the potential for vapor locks if your fuel lines are long, rise a lot or get hot.

You cannot adjust the carb for octane rating, the only thing you could adjust would be compression ratio, if it is to high you could get pre-ignition (pinging) but I have not found this to be a problem with the Jabi.

Rough running could also be dirty exhaust valves, electrical problem (coil ?) or if the engine is not one with hydraulic lifters the valve clearances (should be .010) could also cause it. If your plugs foul quickly (less than 100 hours) there is something else wrong, maybe to rich but the Jabi carb is auto compensating for altitude, or stuck oil rings.

The smoke is disconcerting, I have never noticed smoke from mine or others operating from my flying field ! Does it use a lot of oil ?

It might be worthwhile to do a compression and blow-by test on the engine.

Good luck and please let us know what it is when you solve the problem.

Fly safe,
Rudi

[bosbok]

Neophron,don`t be shy to call Len Alford at Jabiru SA in George about the problem. They work with those motors every day.
I phoned them last week about a choice of radio and Gareth (who does their radio installations) was very helpful. Phone Jabiru and ask Jaqueline (she answers the phone) who you can talk to about the problem with the motor. 044-876-9991/2.
Good luck !

[Flooi]

Also phone Willie van Wyk at 072 31777 68
He is well known Jabiru Technician here in Gauteng. He does maintenance
on Jabiru at many flight schools and private owners. I found hom very helpful.

Regards

[Neophron]

Thanks all.
Have done the above...This is a brand new motor. All of the answers leads to avgas in stead of mogas. (Heard of 95UL turned out to be less than RON 90 after being tested )
Will give the plugs a scrub and change the fuel.... lets see what happens.

[Rudix]

Thanks all.
Have done the above...This is a brand new motor. All of the answers leads to avgas in stead of mogas. (Heard of 95UL turned out to be less than RON 90 after being tested )
Will give the plugs a scrub and change the fuel.... lets see what happens.

Yes, it could be pre-ignition, not all 95UL are created equal and age also causes the RON to drop....

Lets hope it solves your problem !

[James Bentley]

I posted I reply to the board but somehow it dissapeared into cyberspace.

Here it is again in condensed form...


I would say you have a mixture problem with too much fuel pressure, smoke and black plugs are indications of this. If you have an electric pump in the system feeding into the mechanical engine pump, test again without the backup pump on and change your plugs. Your mag drop is caused by the now dirty plugs firing in a rich mixture, that is why the roughness has occured on both mag circuits at different times isolating an electrical problem.

The Jab engines are sensitive to intake design, make sure the scat hoses to the carb from the airfilter are not restricted in any way, keep them as straight as possible with few bends. We have learnt a great deal over the years about getting airflow through the carb and into the cylinders equally, very important for cooling and efficient power. Net result, a long lasting reliable engine

[bosbok]

Have you sorted out the rough running ?

[Neophron]

Haven't had much time lately but we are working on it. We narrowed it down to either the fuel or air intake. Will have more info after the weekend. Thanks so far for all the interest. Wil keep you posted.

[Neophron]

So all the mogas was drained and replaced with avgas. They also decided to to take the scat housing of and give her an open carb, no restrictions. As soon as thy got air born the trouble started. Rpm dropped to below 2300... they managed to stay just above the stall and the trees On the ground you could see smoke coming from the exhaust, while doing the treetop tap. The problem seems to be getting worse Could it be to much hot air from the exhaust? Is their a serious problem with the carb? Well the point is that the mixture is to rich, but what next?

[justin.schoeman]

Getting hot air in the induction will make the mixture leaner, not richer.

Does the problem always occur on or after take-off? Maybe its related to the angle of the aircraft. Have you tried ground runs at take-off attitude? If it is angle dependant, it could just be that the float level is too high, and you get some raw fuel into your inlet once you left the nose high enough.

[John Boucher]

Just a question or three....

I'm with Justin on this..... I know of someone else who had similar problems - just reversed though!

Have you checked the float level?
Is the needle & seat not getting stuck open so you overfuel?
Does it happen when you put the fuel pump on or off?
Is there fuel lying at the bottom of the overflow if you leave the fuel cog open overnight?
Are the plugs fouled - some of them or all of them?