Rotax 912 ULS Running Rough

[DHeal]

In addition to the RotaxOwner videos, there are a couple of videos on YouTube that depict the servicing of Bing carbs -- not necessarily by the book but they do have some good visuals of the carb's internals.

[DanH]

Originally Posted by DaleB

Is there a compelling reason to ship them off to let someone else overhaul, or is this a no-brainer for guys who have some clue which end of the screwdriver is pointy?

No-brainer.

CV Bings are very simple, and have not really changed in 40 years.

Worst case, you throw them in a box later and ship them to a shop.

FYI...We lost a 2 stroke Kitfox here some years ago and traced the fuel stoppage to a small piece of trash hidden in the carb's fuel inlet nipple, i.e just upstream of the the float valve. Nobody ever looks there.

[todehnal]

Originally Posted by bob1393

Thanks Scott and others for the reply. We have the new floats and did check them at 200 hours and they were fine. We did not check them again at 400 hours. We will check them now and the gascolator also to see if there is any debris or contamination as well as weigh the floats.

Bob

Hey Bob, Were you successful in solving your carb problem? I have the same problem and I am currently working on it........Tom

[scottmillhouse]

I ran into the same issue in December and did an engine shut down and power off landing. Went through many carb clean/flush with no debris evident. Ended up draining all auto gas and switch to 100LL with fuel system flush. No problem since. Was thinking old ethanol gas had some fuel line deposits.

[bob1393]

Todehnal - next morning it started and ran perfectly. We did swap out the Ducati Voltage Regulator. We've been flying it and have not had any issues. I'm thinking dirt or debris in fuel line someplace or in the carb that has worked itself through. We're coming up soon on the 500 hour inspection and we'll see what we find. Let me know if you uncover anything.

Bob

[todehnal]

Hey Bob, glad yours is running well. I'm still in trouble here. I replaced the plugs, pulled the float bowls and inspected. I did adjust the fuel level slightly. Those were the easy things. Next, I plan to pull the carbs and do a tear down inspection. From the replies that I've received, most suggest that the likely suspect is a carb problem. It is hard to diagnose. You would think that a shut down and inspection of the plugs after a rough run situation would point you to the problem. Apparently that is not the case with Rotax. I understand that the rough running shakes the **** out of the carbs, the floats go nuts and flood everything. In my case, all four plugs in cylinders #1 and #2 were totally sooted up, as was the tail pipe. I will post any finds...........Tom

[DHeal]

Also check for debris in the return fuel line metering orifice.

[todehnal]

Originally Posted by DHeal

Also check for debris in the return fuel line metering orifice.

Now that does surprise me that this could cause a rough engine, but it is an easy check. Thanks.....Tom

[Art_N412SB]

This is Art, one of Bob's partners. The problem with our rough running engine was some contamination in one of the carb float bowls. We think the contaminant was from chaffing of one of the floats. Keith (one of the three owners) found a small initially hard object. After extracting it from the float chamber he was able to crush it between his fingers. We think it would intermittently clog the jet causing the engine roughness. We have flown several hours since without any problems. Also, Lockwood in FL was very helpful in steering Keith in the right direction.