Fuel smell and transponder fail caution

Brought my RV-12 SLSA to my mechanic today.

The brakes issues are detailed in another thread.

Coupe of other things arose which we weren't able to resolve so I'm asking here if anyone has any comments?

First, cool morning, after putting master switch on, then avionics, got "ADSB-IN Fail due to Transponder Fail" yellow caution on the Dynon Touch screen.
I wondered if the transponder does a self-test and I hadn't switched the avionics switch on quick enough. I pressed the caution button and message stayed. Did it again and it went away.
Second flight today I got the same message and got it removed. Third flight I didn't get it.
I did notice that today there were a lot of instances where the Skyview would display Partial ADSB and then alternate with Full. This may be normal but I haven't seen that before.

Lately, I've also noticed a fuel smell both after start and after shut down. After start it goes away after a few minutes. I noticed a brownish (93 Non-ethanol fuel stain) below the carb, left side,where it looks like there may have been a couple of fuel drips. We couldn't find any leaks or anything loose. Nothing obviously dripping.
I'll clean the area and look for any more leaks. Mechanic noted the clear plastic overflow tube on left carb had some fuel in it and we wondered if there was a drip onto the flat metal splash tray below it whether the fuel would quickly evaporate leaving the smell.

Mechanic said to ask you guys about why Vans wants the fuel pump on all the time the master is on, which is how my SLSA is set up. He noted other Rotax engined planes he works on have separate fuel pump switches for t/o and landing, and is that way in his KitFox.
I said I'd ask here. He's wondering if the pump being on so much is overfilling the carb, especially the left one causing fuel to drip out and causing the smell.

As always, any comments or info will be glad received!

Thanks!

Search the RV-12 forum for Roger Lee's posts about carburetors. If I remember correctly, he recommends removing the bowl and cleaning the float valve, and checking the bowl gasket.
As for the electric pump overfilling the carburetor, that will not happen unless the fuel pressure is extremely high. I do not know how high but suspect it would have to be more than 10 psi.
The electric pump runs continuously on most RV-12 for safety. Engine driven fuel pumps on the Rotax can leak fuel when they fail.
Joe Gores

Fuel Smell

Hello,

Ok, so I recently also had a slight fuel smell which I could never find. I almost stripped the whole plane looking for a fuel leak.

We found it, thankfully!!!

Please check the floats in the carb bowls. Mine were no longer floating in the fuel that was in the carb bowl. This caused the fuel to leak out of the overflow tube and on to the tray under the carbs. The fuel evaporated before we could get the cowl off the aircraft and so we didnt suspect the carbs.

I replaced the floats in both carbs as well as balanced them as well. My 12 feels like a new aircraft. Smooth ....and no more fuel smell!

Check your floats!

Top Cat said:

Brought my RV-12 SLSA to my mechanic today.



First, cool morning, after putting master switch on, then avionics, got "ADSB-IN Fail due to Transponder Fail" yellow caution on the Dynon Touch screen.
I wondered if the transponder does a self-test and I hadn't switched the avionics switch on quick enough. I pressed the caution button and message stayed. Did it again and it went away.
Second flight today I got the same message and got it removed. Third flight I didn't get it.
I did notice that today there were a lot of instances where the Skyview would display Partial ADSB and then alternate with Full. This may be normal but I haven't seen that before.

As always, any comments or info will be glad received!

Thanks!

Click to expand...

I have noticed those messages when I was just doing some engine runs without the avionics switch on, must be that the transponder is hooked up to the avionics and the ads-b to the master? I dunno.

Also, my avionics guy came out to do my 24 mo transponder check and he was very familiar with Dynon, his equipment found it, but could not interogate it till I pushed 7/8, went into the transponder set-up menu, and changed something from AUTO to NONE....then it worked fine.

The immediate things come to mind with the most common fuel smells.
Leaking carb bowl gasket. If you don't have a drip try the any evidence gets blown away. If you have a drip tray then usually there is at least some residue from the drips. This one is the most common. The second which has come to light more recently is a sinking float. It causes the carb to over flow out the vent tube and then you smell the fuel. Both are fairly easy to check. The sunken float can be checked just by starting the enngine and run it up a to about 2500 rpm and look at the vent tubes. If there is fuel in either one time to check the floats.
One last thing. If the carb sync is quite a ways out or the rubber engine mounts are really bad then the engine will shake making it hard for the floats to control the fuel level and fuel can get vented out the vent tubes.

Last items are a leak around a fuel fitting or a fuel test valve leak.

Top Cat said:

Brought my RV-12 SLSA
Thanks!

Click to expand...

I have the fuel vent mod done and my airplane has been sitting in the hangar with pretty close to a full tank and I have noticed a fuel smell, esp on the right side below the cockpit...it's the new fuel vent!

At first I thought I had a leak, checked everything, then I was under rechecking the torque on the landing gear nuts/bolts and that is when i figured it out.

Keep in mind right now the temp has been fluctuating from 65 to 100 in AZ.

Since you have an SLSA I assume you also have the mod done (it's a second small tube beside the main fueling tube and leads into the back and goes down and out the bottom of the fuselage....there is also another smaller rivet hole as well that is a breather for the vent.

My SLSA has the mod.

During the really hot weather I've heard a hiss of air as I pried off the fuel tank cap. BTW?my cap seems very hard to take of and on?annoying.

I've had a little fuel gurgle out of the overflow..I figure expansion.

However, I'm getting a fuel smell after start which goes away and it's present again on shut down. Couple of stains running back on pilot side under the cowling. Drips appear directly below the carb. Splash tray is always clear and so is overflow tube.

So far, we're monitoring it and I'll clean the area underneath and watch for new drip stains. The oil change is coming up and we'll look at the carb then.

BTW?my cap seems very hard to take of and on?annoying.

Click to expand...

You can easily adjust your fuel cap by loosing the bottom lock nut a few turns. Then grab the bottom plate next to the nut and turn it the same direction as the lock nut, about 180 degrees at a time. Then retigten the the lock nut, then reinstall the fuel cap and test for fit and tightness. Repeat until desire tightness is achieved. I few drops of oil like Mavel mistery oil near the pivot point on the top of the cap wont hurt
either.