I have a Nexstar select,it is running good except today i was bench testing the os46fxi engine and i noticed very tiny air bubbles in fuel line.Should there be ANY bubbles in line or not?If not what is the best way to test for leaks.It runs fine at vertical and idles good,just wondering if i have the beginning of a problem. Thanks

Very tiny bubbles are not terribly unusual and often caused by vibration. Of course I don't know what YOU call TINY but I would probably not be too concerned.

Enjoy your plane and go FLY.

I would agree with bruce, however if the tiny bubbles are not to "tiny" I would say replace the fuel lines since that is cheap in cost. Also on my nexstar with the same engine I started to have problems once and I found it to be the rubber stopper, at your fuel tank, that your fuel lines go thru. And it was that the screw that you tighten the rubber to form a tight seal for the tank was starting to get loose and that did allow air to get in.

with proper isolation of the fuel tank (foam padding) there will be no bubbles, even tiny ones. any bubble regardless of size leans the air/fuel mixture. on high RPM applications even with the foam you can get foaming of the fuel when the tank is below 1/4 full but you shouldn't get any when it's topped off full. if you're getting them even with the tank full, it's sucking air somewhere, replace the lines.

kc

take your fuel tank out and pressure test it in water to see where the leak is

doesn't work if the leak is in the clunk line.

kc

I test mine by pulling a lb. or 2 of vacum on it. If the gauge drops, I have a leak, if it holds steady, it`s good to go. don`t use to much pressure or you can suck the tank flat. lol

I didn't find out that the stopper on my Nexstar fuel tank was coming loose until I filled my fuselage with nitro fuel!

This is a good thing to check periodically. If you ever happen to fill your fuselage with glow fuel, packing it with kitty litter will help soak up the oil and fuel residue. Hopefully you won't need to know this anytime soon.

If there are no bubbles before the remote needle valve and there are bubbles after it you have one of the many leaky needle valves the 46FX came with. Could be the o-ring around the needle valve or it could be leaky nipples to the tubing. The needle valve for the Tower 46 is a cheap replacment.

again that'll do nothing at all for checking the clunk line. most of the time problems such as the aforementioned are a result of the clunk line deteriorating due to the submersion in fuel and the clunk weight flopping it around in the tank during flight. fuel tubing is cheap, replacing it isn't allot of trouble and i replace all my lines every year, prevents 99% of any fuel line problems that might of occurred and gives you the opportunity to inspect the tank/stopper as well.

kc

No one ever said there WAS a leak.

Tiny bubbles CAN be a problem, but then again, they can also make no significant difference at all ("Significant" being the operative word here)

And since you can go crazy trying to fine a leak that may not even be there (The bubbles can very easily be caused by normal engine vibrations), as long as it's not harming anything, don't lose any sleep over it.

Didn't I say that in post #2?

Yes you did Bruce.

Then the "Experts" came in and started telling him how to fix an imaginary leak

if you're getting bubbles even with the tank fully topped off there is a leak and while it may not make a hill of beans difference to you, those of us in that 'Expert' class run performance engines and it's a very big deal. ignoring the problem like it's nothing, isn't going to make it go away and chances leaking fuel into your airframe but i guess you have to be an expert to realize that.

kc

This is not a "performance" thread, so we're not trying to tweak every last RPM out of an engine. The OS engines that have the remote needle valve will create very tiny bubbles between the remote needle valve and the carb, BUT the engine will run just fine like this. Bubbles in the line that you need to worry about are ones between the tank and the remote needle valve. A good rule of thumb here is "If it ain't broke don't fix it". If your engine is running fine but you have the tiny bubbles between the carb and the needle valve don't waste time trying to fix a problem that doesn't really exist, but if the engine isnt' running well then try to figure out what's going on.

Ken

it doesn't matter what forum it's in, he asked "Should there be ANY bubbles in line or not? and the answer is NO regardless. a leak anywhere, even at a remote NV, is a leak and is not supposed to be there. you tell someone who is new to the hobby 'Oh it's no biggie, don't sweat the small stuff' and they'll always have that same attitude. if it's leaking, it's broke, it needs fixing.

kc

WHO SAID IT WAS LEAKING????

With most of today's ARF's there is no room to pad the tank with foam.

And I defy anyone to fill a tank to full capacity and have NO air in it.

Now while foaming can be a big problem, a minor amount of foaming is not unusual - nor is it a matter of concern.

Certainly not so much that I would tell someone who is flying a Nexstar to pull their tank and re-plumb their fuel system.

if you're getting fuel foaming to the point of induced bubbles in the clunk with a tank 'mostly' filled then there is still a problem, maybe one should check the prop for that missing blade.

kc

I'll be sure to do that from now on KC

Hey Minn, I found your missing blade. Do you want me to mail it to you? Maybe you can forward it to bilbo5 so he can fix his bubbles.

Tiny bubbles in the line, make me unhappy and not feel so fine , hickup!

yep, I've got an ARF trainer. Why can't they leave a little room for foam? It had the tank in it when I won it at a fun fly. I've got to go back and pull it a part, cut down the lite ply its mounted in, and put some light foam in before I ruin my engine. Yes, I know. I like running my planes lean. With the extra air at high speeds in is heating up and quitting. Did anyone ever tell ya its a fast way to burn up a good engine?

trying to tweak every rpm out of a trainer is like indexing the spark plugs on your moms soccer van....pointless.. in 1/2a engines I get a lot of foaming bubbles while fueling that settle as larger (tiny) bubbles ..basically just make the engine run a bit leaner...as long as its not affecting the performance..ie if you can hear a difference, there may be a problem......from what youve said it doesnt sound like a problem...if the condition gets to worsen, then start to check for problems, if not....IF IT AIN'T BROKE DONT FIX IT...and if it deadsticks,, slow wide turns, if you try to do a 180, it will fall out of the sky...it happened to me with a .25 trainer after 100 deadsticks, thats the only way I land..as most of my planes dont have landing gear......Rog

I figure that since the tiny bubbles are there when I set the needles they are taken into account and do not hurt anything.
If they stay about the same for the entire tank they won't matter to you at all.
It is good to pay attention to small things like this though, because as soon as your glow plug starts to die and the engine does not run right there will be plenty of people that point out those tiny bubbles. Just remember that if they are the same as they have always been and the engine used to run fine it is unlikely they are suddenly causing a problem.