Severe Vibration

[Darryl]

I own a 2010 CTLS. I am experiencing severe vibration in my engine when I pull off the throttle for descent - otherwise the engine runs fine. This vibration starts at about 4700 RPM.  The run-up is fine. There is plenty of power for takeoff and it cruises just fine. My mechanic replaced the carburetor floats thinking that was the problem. That didn't help.  Any ideas?

[Roger Lee]

Hi Darryl,

 

Sounds like the carbs are out of sync. I would have doubted the floats were to blame. Do a pneumatic sync at 3500 rpm and of course at idle too. Some Rotax engine even though synced for idle and higher rpms do get out a little as you throttle down, but that usually happens in the 2200-2500 range if synced at the 3500 mark. Nothing you can do about it except don't fly at that rpm, which we usually don't.

[Darryl]

Thanks for the tip, Roger. We have tried syncing the carbs. Still vibrates. I emphasize that the vibration is severe. It is pretty frightening. The idea of avoiding the RPMs in the vibration range just won't do. This is a new problem. I have 170 hours on the engine. The previous 160 hours were smooth at all RPMs. One clue is my mechanic tried and failed to install the new fuel pump recommended by Rotax -- it' s a long story. We are still using the original fuel pump. This probably has nothing to do with the vibration problem.

[coppercity]

I had a 2007 CTSW do that to me one time when one of the carb floats was stuck with some gasket debris. It was smooth at idle up to about 3500rpm and at full throttle, but was really rough at around 3800. take the carb bowls off and take a look.

[Darryl]

I had a 2007 CTSW do that to me one time when one of the carb floats was stuck with some gasket debris. It was smooth at idle up to about 3500rpm and at full throttle, but was really rough at around 3800. take the carb bowls off and take a look.

 

We already replaced the floats in the carbs. BTW, the problem does not replicate on the ground. I put on the brakes and ran the engine at full throttle, and then pulled back the throttle. It ran smooth as silk at all RPMs. Makes me wonder about the prop or reduction gear.

[Tom Baker]

I had one at 165 hours have spells of running rough. One of the slides in the carb was gummy. Cleaned it up and went ahead with the 200 hour carb inspection all was good after. Also make sure one of the clear balance tubes has not come off.

[Tip]

I have had this happen to me several times on my 2008 LS . It was the left carb balance tube. It was clamped with a nylon tie and came off at the carb. The tube makes a sharp bend and has pressure on it. I fixed it by using a spring clamp bought at an auto parts store. I saw this same condition on a brand new LS Lite at Flight Design US.

[Darryl]

Thank you everybody for your suggestions. I have forwarded every one to my mechanic at Arlington Airport - north of Seattle. I will write a post to this thread once we figure it out. In the meantime, keep the suggestions coming. Much appreciated. Darryl Swenson, Seattle WA.

[Jim]

Check your motor mounts. It's an annual inspection item,

but it's been known to be missed. I was flying with three

loose bolts and one completely backed out.

[BMcCand - N248CT]

I also had severe vibration when throttling back for descent, around 4000 RPM. This was in a 2006 CTSW, and the carb ventilation

tube had slipped out of the air intake fiberglass air box. I think this is different in a CTLS, that uses the Rotax air box.

As said above, make sure the clear carb ventilation hoses are connected and not crimped.

My problem was just after a Rotax mechanic had done the 200hr service, but he was not familiar with CTSW airframe.

[Darryl]

Thanks everyone for your tips. Indeed it was the carb vent hoses. Besides that, we replaced the floats in the carbs. It may be my imagination, but it seems like the engine runs better than it ever has. I credit the carb float replacement for this.