912ul rpm drop @ full power

[Zorro]

Whats the static line? I have checked the balance tube?

[Dave S]

Regarding the " Static Line", I believe Rotax calls this an Air Vent Line - it is a small plastic tube (about 1/4" & 120 mm long) hooked to a fitting on the engine side of each 912 carburetor - near the rubber manifold connector. If a person has the optional airbox - the two air vent lines are connected to nipples on the airbox. If you don't have the airbox - I believe they are left to hang near the carburetor - I am not a rotax engineer; however, what I have been told these are for is to balance the air pressure beteen the inside and outside of the carburetor. If they don't work (plugged) - it messes up the air fuel mixture.

Sincerely,

Dave S

[Zorro]

Ok yes on mine they go back into the k&N filter, when they come out it runs rough and I get a strong fuel smell in the cockpit.

[napierm]

I know this is reviving an old thread but I have a similar problem. I picked up a CH601HDS from upstate NY last weekend and flew it home. Checked it out on Sunday and it flew great. Good climb, handles well, faster than what I'm used to but fun.

On the way home Monday the engine lost some power. Like 20 minutes out from Saranac Lake west of the mountains this stupid thing didn't want to climb well and I don't know why. No where to land.... Crap.

So landed when able a few miles south of active MOA. Checked everything I could with limited tools. Engine seems smooth and reliable just gutless at full power.

Compression test consisted of pulling prop and feeling quality of compression on each cylinder and listening to exhaust and intake for leaky valve. Far as I could tell fine.

Checked float bowls - floats riding high and level looks right. No sign of debris or anything wrong in jets. Don't know about carb sync but that shouldn't affect full throttle much. Again, everything seems smooth so sync doesn't seem likely.

Engine seems to be getting enough fuel. If anything the fuel consumption is a bit on the high side. Air filters are supposed to be fairly new. Dont' know what the static RPM's are because the @!@#$!! tach has gone out.

Engine start running some better and I basically nursed it all the way home to 6ga4. My route was over a few foot hills but no mountains - kind of a trick from NY and avoiding the 60nm ring around DC so went through Shenandoah Valley. Very long day and a half flying because of fuel stops and reduced cruise speed.

Was well worth getting as the plane flies very nice, not a Kitfox, but nice.

So I've got a tiny tach coming and will start debugging when I can make some reasonable comparisons.

Any words of wisdom on similar problems?

Thanks in advance,

Mark

[HighWing]

I recently checked over the theory behind the Bing carburetor and this is what I think I learned. Idle fuel flow is set with the idle jets. Mid range is set by needle position and is affected by the diaphragm, spring and balance tube. High RPMs are set by the venturi effect through the open pathway when the piston is fully up - powert is determined by the butterfly and the suction of fuel through the jet. With that in mind, if it is carburetor related, My guess is that it is a fuel flow issue. Has the airplane been sitting for any length of time before you bought it, or has it been flown regularly? Has the throttle linkage somehow been compromized. I once had an issue with the engine faltering at high RPMs and I traced it to a firesleeve clamp that was pinching the fuel line. Keep in mind that if it is fuel flow, by the time you taxi and check the bowls at idle, there would be sufficient fuel to fill the bowls. The same is true with the plugs. Lean running at full throttle would be followed by normal ratio at taxi and the actual plug appearance - lean at full - could be masked by several minutes run at idle while taxiing.

If it runs smoothly at all throttle settings except high RPM I think you could discount compression issues, though that is easily checked with a differential compression tester. With the tester in place on each cylinder, If it is the intake valve that is leaking, you would hear the leak hiss through the carburetor; if it is an exhaust valve leaking, you would hear the hiss at the exhaust.
Lowell

[napierm]

Idiot question: what do you expect out of a mag test on a 912? RPM's?

[ClickClickBoom]

Idiot question: what do you expect out of a mag test on a 912? RPM's?

912 operators manual
10.3.5

4000RPM

300RPM drop max

120RPM difference between A&B circuits max.