Float suspension brackets

Thanks Roger

I've stripped both carbs completely and checked that all jets and passages and orifices are clear. Squirting cleaner up where the idle jet screws in I get a clear stream from both the progression orifices and the idle orifice. I went through the starter carb as well. (Incidentally the disk has 4 dimples in it but only 2 are drilled through but photos I have found suggest that is normal.) I checked the diaphragms and all the O rings except the throttle shaft. Both pairs of floats show 6gms on my scales (only 1gm resolution). Carbs have only done about 100hrs, but spread over some years and with a full rebuild by Rotax UK service agent after being in a hangar fire at 50hrs.

I've put everything back, set all the cables carefully and vacuum synched. At idle (1800) both gauges read the same, about 17".  Increasing rpm you get a bit of variation between them but always within about 1" and at 4000 the reading was equal, I think about 7 or 8" , looking at a pic of the dial.

There's no improvement. Slightly rough at idle, worst at 2700, magically smooth above 3000. I don't know what else to try. I can't imagine it being to do with sparks, although in the vibration range it is worse on one mag than the other but above 3000 mag drops are equal and no significant roughness. I also can't imagine it's prop balance (Airmaster constant speed with 3 WarpDrive blades 62"), that wouldn't magically go right at a certain speed.

I'm open to suggestions!

maybe it isn't carbs. Rough running can be caused by the gearbox and may need to be inspected and the prop dynamically balanced. They can get out of balance.

Hi Roger 

My LAA Inspector and I have stripped the gearbox and checked the splines, the washer preload etc. (We didn't remove the shaft so as not to damage the bearing.) The moving parts have only done 100hrs from new. After the hangar fire the gearbox housing failed the hardness test so it was rebuilt in an inspected used housing (with a new main bearing).

I borrowed a dynamic balancer, according to this the prop vibration was about 0.15ips which isn't brilliant but is acceptable. The instrument was giving very inconsistent readings of the angle so I didn't try any weights. To me it doesn't feel like a balance problem. The vibration disappears quite sharply at 3000rpm and it goes almost completely smooth, it's not like an unbalanced car wheel or washing machine where it finds an offset centre of rotation within the compliance of the system. The Europa rubber mounts are very stiff, not like the normal Lords, you would certainly feel it.

Increasing pitch makes it rougher but I think that's generally true anyway.

Pulling the choke part out doesn't really affect the roughness, nor does turning the idle mixture screws in by 1/4 turn.

I'm out of ideas! It's also been looked at by Andy Draper who you may know of - ex Europa and now in LAA Engineering - and he couldn't come up with anything. He and others have said ignore it, just avoid that rev band, but I'm not keen on that. It's not nice during warming up and taxiing or throttled back on approach.

Roger, just about the only thing I haven't checked is trigger coil adjustment, What are the effects of the gap being wrong, anything predictable or just generally erratic ignition?