flying_frog

I have a 3 yr old OS 61 FX. The engine keeps dying. I noticed that I am getting air bubbles between the needle valve and the carb. I replaced all fuel line...still bubbles. I tightened everything on the engine...fuel inlet, needle valve holder assembly...still bubbles. I called Hobbico, they say to replace all the O-rings and fuel inlet assembly. Of course they could not sell me the stuff. I have to go to my LHS.

Before I go ahead and order these parts (or just buy a new engine) any other suggestions?????????????

Thanks for your help.

[sm=spinnyeyes.gif]

Primodus

My Feedback: (56)

I had a similar problem on my 61FX recently. I replaced the Needle valve and the holder that goes with it (about 20USD total from tower). Also replaced the tubing between the carb and needle. Another issue plagued me as well, foaming of the fuel. I was getting nasty vibration that foamed the fuel if the tank was over half full. I know because I can see the back half of my tank in the J3 Cub I put it in. Once the tank emptied some the foaming became relatively non-existent. I hope this helps.[8D]

FHHuber

Slip a 1/4 inch piece of fuel line over the nedle valve to aid the needle valve o-ring in sealing air out. The needle's O-ring slowly shrinks with age and heat... and then air creeps down the needle threads. You can fly for years with this fix. (If its what is needed...)

Did you also verify that the air leak is not from a cracked brass or aluminum tube at the fuel tank? How about a hole in the clunk line inside the tank (the clunk line hole usually starts giving problems below 2/3 full tank level Sometimes as low as 1/3 full before the air starts getting picked up.)

I bet you just need a needle valve o-ring...

flying_frog

I did replace the tubing between the needle and the carb as well as tubing from the fuel tank to the needle and muffler. I don't think the brass tubing inside the tank is cracked because I get no bubbles before the needle.

One thing I did forget to mention is that I only get bubbles at 1/2 to 3/4 throttle. Anything more or less, I'm ok. Sure sounds like an O-ring problem here. Hopefully the LHS will have this in stock.

wrongwaywayne

If you pack your fuel tank too tightly with foam the vibrations will introduce bubbles into the fuel. If the fuel line is too big that can introduce bubbles as well. Try removing some foam. Check all the lines again.

I have had similar problems but have always been able to solve them. In case you don't know , its important to fix that because the air bubbles can lean out your engine and even cause it to quit in the air.

FHHuber

Causing it to quit is not as bad for the engine as a lean run that lets the engine keep running at reduced power... THAT will fry the engine.

Having an engine go dead unexpectedly can either be a minor annoyance... or can destroy the model. There's usually not much in between. You either manage a decent dead-stick landing or plant it firmly. If you have altitude... its almost always just annoying.

Wayne Miller

Hi,

I hope I can explain this OK.

Check your fuel line to the "clunk" in the fuel tank and make sure it is very flexible. Make sure it is not too "stiff".

If it is too "stiff" and "just" allows the clunk to fall with no fuel in the tank, then the stiff fuel line will act as if it is under "spring" tension may cause the "clunk" to "bounce" during vibration. This will cause the clunk to go above the fuel in the tank. This will appear as if fuel line has an air leak.

Make sure the fuel line in the tank is very flexible and the "clunk" is heavy enough to keep it in the bottom of the fuel tank, no matter what attitude the plane is flying or how much fuel is in the tank.

Hope this helps.

Let us know what you find in the end.

Best regards,

Wayne Miller

flying_frog

Thanks for all the help. But unless I am totally missing something, if I do not have any bubbles whatsoever between the tank and the engine, why would the tank, clunk, fuel lines be an issue. Even though I replaced all that anyway. What am I missing.

I was able to get a replacement needle valve yesterday. Will do another test run tonight. I have a feeling that the engine might be shot. When I went to unscrew the valve, it was VERY tight against the crankcase. I think my last crash may have done more damage than expected...just don't know why it took a year to surface. And yes, it was a SPECTACULAR crash! Wasn't much left to take pics of though.

FHHuber

Might have to RTV the carb to the main case to prevent an air leak... when the carb gets spun in the hole by an impact... you get some slop there.

But unless the crankshaft is bent... or the case itself is cracked, a crash VERY rarely does serious harm to the engine. The carbs suffer quite often from the collapsing spinner.

flying_frog

Ummmm...what's RTV.

Also, this thing runs really hot. It's starting to scorch the oil residue on the outside of the engine. Could that be from running too lean or do I really have some major damage.