Dripping Fuel

[Taxus812]

I’m trying to locate the source of a minor fuel leak.
Can fuel blow back from the carb? I’m a bit of a noob so here is a bit of history (hope I don’t make you cross-eyed)
I have on OS 50 Sx Hyper with a Hatori pipe. The total runtime on the engine is 1H 30M (9 flights) I have been breaking it in and learning a lot in the process. It seems to be running clean and even now but it drips fuel (not a tone but more than I like). The low speed needle is set great (clean transition from low to high, no power loss or hesitation). High is still rich. The engine temp is about 130- 156 Deg but I haven’t pushed it.


At first I was massively rich on both the Low and high needles (followed manual and had it three turns out WAY too rich). First flights fuel was just everywhere. (Too much to figure out where it was coming from). I discovered I had a leak at the muffler joint. I cleaned it up, added RTV and flew it. Most of the leaking stopped. I leaned out the high and I was then able to set the low speed needle. (Much but still dripping fuel).

I cleaned the engine up and took a flight just to look for leaks. I spooled her up and watched for leaks. I couldn’t see any. If flew for a few and could see the screws on the backplate weredripping fuel. There was also fuel on the side of the engine but mostly on the backplate screws. I figured I had a leaking backplate gasket. I started to pull things apart and I noticed that the inside of the fan shroud and head was actually soaked. This makes me question if the fuel was coming from the backplate.

The gasket on the backplate looks fine???? Could it be blowing out of the carb?


I did a bit of searching on troubleshooting fuel leaks and thought I would post to get you thoughts.

[Taxus812]

Well I found the answer on another site. It was the muffler after all. It was just spraying under high pressure when I loaded the engine.

The issue was resolved by removing the muffler, cleaning the RTV off and resurfacing the joint.

To resurface:
1) I used 3200 grit Micro Mesh and wet sanded on a piece of glass. I sanded the joint lengthwise so not to round the edges. (http://www.sisweb.com/micromesh/).

2) Sand until it is totally flat and no fine groves or residue showed.

3) Use a Sharpie marker and cover the entire surface of the joint. Once dry sand until there is no more black marker on the surface. (This makes sure there are no groves you can’t see)

4) Clean the exhaust on the engine and make sure there is no residue

5) Mount the muffler with no RTV or gasket.

6) Heat up the engine and tighten the bolts

No more leak.