Wednesday, September 26, 2018

Sunken Float

During my last Annual Inspection I overhauled the Bing carbs as they had exceeded their 200 hour mark. I did this despite the feeling that leaving things that work alone is usually the best strategy.
My main worry was that after all the issues with the Bing floats that Rotax had for a long time, I should probably go and finally see how they were doing after such a long time submerged in gasoline. And indeed, I did find two that were a bit heavy. Mind you though that despite their weight I experienced no issues with the engine. Not at idle or low RPM and of course not at WOT.

A few weeks ago I started my engine in the morning and found it to be reluctant to come to life. It sounded a bit like a Diesel engine, with heavy vibrations and very rough running coming out of idle, barely maintaining idle speed. My first guess was that one of the cylinders was not firing properly.
Pushing the idle during warm-up close to the 2500 RPM mark made it better, and the engine ran fine at higher RPMs so I decided to go ahead and take off.
At my destination I throttled back to start the decent and the engine behaved a bit rough again and I could smell gasoline. Yeah, that definitely worried me, so I grounded the plane after my return to give the engine a thorough inspection before further flight. As a busy man I didn't get to it until last weekend where I took off the carbs opened the bowls and re-inspected the floats.
One of the just recently replaced floats (one of those that were supposed to finally end the problem of sunken floats) weighed in at 8.5 grams!

Notice the markings on the float in the picture above. This is definitely a new style float and it took just a few months to almost triple its original weight. Given the price of these parts this should never ever happen. The other new style float I found was at 4.5 grams and two original floats I left in the carbs were at or below 3.5 grams.
I replaced the 8.5 gr float with a new one and matched the 3 others for lowest pair weights and installed them in the carbs.
The engine fired up and ran just fine, no coughing, no fuel smell, no rough running at low RPM or idle.

I am getting tired of these Bing carbs and am thinking again about replacing them with a TBI...

-- Update --

I researched this matter a bit more as I was very annoyed by the fact that these "latest" floats were still showing the old problem of absorbing fuel. Turns out, I must have bought the carb rebuild kit right before a newer new float was released. I have the 861-185 version which was obsoleted around September/October last year which is right after I had bought my rebuild kit. The latest product number is 861-188 and the leisurely determined price is a whooping $151 for a pair. Which is about 15% of a TBI ....
I found details about the float tale here:

The following picture is a nice example how you can identify a float issue without even utilizing a scale.

When the brass pin that is supposed to push against the lever that controls the inlet valve on the carburetor is below the fuel line in the bowl, it cannot perform its function properly. The left one is clearly below that line!