Engine misfire

[ricky m]

http://www.jabiruownersgroup.org/viewtopic.php?t=324&p=1633 this thread seems to be similar to my fault....

[deadstick]

Hi Ricky m, have you checked the carburettor out? I do recall similar symptoms to yours from a friend some time ago and think it had something to do with the density sense line on the carby ( small tube from the side of your carb to the filter box) Might be worth overhauling your carbons well.

 

 

[ricky m]

Hi Ricky m, have you checked the carburettor out? I do recall similar symptoms to yours from a friend some time ago and think it had something to do with the density sense line on the carby ( small tube from the side of your carb to the filter box) Might be worth overhauling your carbons well.

Hi deadstick, checked balnce pipe after second time when i reset choke it was all clear routed well no low pionts...am going to compresion test and leak test on weekend, if all good there will remove and inspect carb:) concentrating on float needle...

 

 

[facthunter]

When you have the carb off check fuel flow rate out of fuel line. Nev

 

 

[Yenn]

2 plugs per cylinder, one faulty and you will get what feels like a miss, but nowhere near as bad as if both plugs go out. Try doing a mag check while the engine is running rough. If one plug is poor, shutting down the other will give a proper miss.

 

 

[facthunter]

Not sure I would recommend that on high power. It is useful with some DUAL magneto set-ups where the gear driving the distributor may have stripped and cause very erratic running. In these circumstances if the faulty magneto is isolated the engine is still useable on the good magneto at below full power in an abnormal situation. Ie get to a place to land not too far away. Nev

 

 

[Yenn]

I was recommending a mag check at high power, purely as a diagnostic procedure. If it causes bad misfiring, you have your answer and can turn the mag back on quickly with very little really rough running.

 

 

[frank marriott]

An occasional mag check at high power in worthwhile.

 

A few weeks ago I discovered one mag breaking down above 2500rpm. Standard pre takeoff check at 2000rpm checked good.

 

Eventually discovered the wires broken inside the insulation where they connect to the coil, sealed and not normally accessible. Rough running only occurring when high current drain occurring.

 

 

[Rodr]

Replace all the plugs preferably iridium almost sure you won't get a miss on full power until they get clogged will prove carby needs adjusting ,I've been there, only missed on full power climb soon as you throttle back to cruise runs as sweet as pie!

 

Rod

 

 

[ricky m]

Carried out fuel flow test today 1.5 litres a minuite at fuel pipe fuel passing through float needle good... Float bowl level 11-12mm removed float needle and flushed found small bit debri in jug but cant confirm from flushing....Spark plugs replaced front cylinders plugs nice couler rear cylinder little sooty when wiped light grey/brown:) Replaced all plugs tightend ht leads,will check again after a flight tommorow get a better idea of colour as was only short taxi ground run...could not do compresion test as mine was wrong size and leak down tester not here till Tuesday :( so nothing conclusive..

 

 

[Yenn]

Plug colour can be misleading. On full power they may be one colour, but after a few minutes at low power in the approach, then idle while taxying in they can change.

 

 

[ricky m]

Plug colour can be misleading. On full power they may be one colour, but after a few minutes at low power in the approach, then idle while taxying in they can change.

Totally agree but a bloody good indication if something has really gone wrong..

 

 

[Camel]

Just another point to be aware of, when searching for a weak plug if you have a infrared thermometer, on landing check spark plug temperatures the coldest one will be the faulty one !

 

 

[BigPete]

I too have had an ongoing issue with misfiring, running rough on take off. Checked everything that's been posted here. Fuel flow, spark plug leads, distributor caps, etc, etc.

 

Then I was given a spare coil that came off a Jabiru that had a cold start kit fitted to it, so I knew it was good. Fitted the coil (the gap was a bugger to set, used thin card board) to what I thought was the bad side. But this made no difference. Still misfired on take off. Feeling that "Murphys Law" was in play, I then swapped the replaced coil (the one we removed) with the other one (the one I didn't touch).

 

This went very smoothly as I had already done it recently (very) and I still had my pieces of cardboard! Took a few turns to get it started (A breakthrough clue, but I didn't know it then) and took off once again still misfiring. Back safely on the ground I decided to put in new plugs (the old ones had only done 30 hours but I was now clutching at straws AND I better re-check the coil gaps. I'm positive that I set them at .0012" but they measured .0017" - WTF!!!

 

So to cut an embarrassing story short I re-set the coil gaps to .0010" (a few thou under to allow for Murphy) and went flying. Climbed like a scalded cat. Problem fixed.

 

Hope this may help.

 

 

[ricky m]

I too have had an ongoing issue with misfiring, running rough on take off. Checked everything that's been posted here. Fuel flow, spark plug leads, distributor caps, etc, etc.Then I was given a spare coil that came off a Jabiru that had a cold start kit fitted to it, so I knew it was good. Fitted the coil (the gap was a bugger to set, used thin card board) to what I thought was the bad side. But this made no difference. Still misfired on take off. Feeling that "Murphys Law" was in play, I then swapped the replaced coil (the one we removed) with the other one (the one I didn't touch).

 

This went very smoothly as I had already done it recently (very) and I still had my pieces of cardboard! Took a few turns to get it started (A breakthrough clue, but I didn't know it then) and took off once again still misfiring. Back safely on the ground I decided to put in new plugs (the old ones had only done 30 hours but I was now clutching at straws AND I better re-check the coil gaps. I'm positive that I set them at .0012" but they measured .0017" - WTF!!!

 

So to cut an embarrassing story short I re-set the coil gaps to .0010" (a few thou under to allow for Murphy) and went flying. Climbed like a scalded cat. Problem fixed.

 

Hope this may help.

Hi thanks for info...its looking good after the carb clean new plugs ect... Compresion test was good and also back using avgas.. Running very well done full power climb too 6000 ft to test.....

 

 

[Yenn]

Get some brass shim to put between the magnet and coil when you bolt it in place. The gap is automaticly set to whatever the shim thickness is. Should be 10 thou from memory.