I'm not a total Noob at RC but I have an issue im about to pull my hair out about. I purchased a Nexstar Select Trainer and flew it a few times and then put it up for a year or so. Recently I get it back out and flew a couple of times with no problems and then took the thing apart to clean it and never run right since. Here is the Issue

I put my finger or the carb while turning the prop to get gas through the line into the carb. I put in the glow plug and get the engine to start. It idles fine and I can rev it up and down with no issues. BUT, If I rev it up and leave the throttle wide open, after 10-15 seconds or so, the engine dies. Not good when you are already in the air. Ive changes glow glugs, all the fuel lines, New fuel, and im at a loss here. Another thing ive notices is that after the engine stops, all the fuel in the line gets sucked back into the tank and a little comes out the pressure line going to the exhaust. It almost seems there is an air leak of some sort but cant figure out where it could be. Hope someone can help.

Sounds like you may have gotten the lines going to the wrong places. Try looking behind the engine you will see three lines coming from the fuel tank. The top line is the "fill" line. The line on the same side as the needle valve should be the "fuel" line going to the needle valve. That leaves the other line going to the muffler as the "pressure" line.

Happy Landings!

Thanks for your fast response.

I have everything in order when it comes to my fuel lines. I will recap tha way the metal elbows are inside the tank.

The fuel line inside the tank in a straight metal tube with the silicone tube on it as well as the clunk. Its on the bottom.
The fuel line with the shortest elbow in the refil line and its pointed down.
The fuel line with the the longer elbow is pointed straight up.
I also made shure the cap on the fuel tank is well tightened.

I hope this helps

Look at the attached diagram and it should explain how the lines should be connected. But brief, here it is:
The line with the clunk is the fuel pick up and should be connected to the fuel input on the carburetor
The line that points the to top of the tank is the vent/pressure line and should be connected to the pressure nipple on the muffler
The line that points to the bottom of the tank is the fill/drain line and should be plugged tightely when the plane is running.

Hope this helps

Ken

You may have the fuel lines connected up the way they are supposed to be, and you could still be experiencing a fuel line issue. You need to examine your clunk line to the carburator very carefully both inside and outside of the fuel tank for any holes or tears.

The issue you're describing can happen when a small tear occurs. The engine can draw fuel at idle speed without any trouble, but once you crank up the engine, the added fuel pressure allows an air leak at the hole or tear in the fuel line and the engine can't pull enough fuel to run at WOT.

Ask me how I learned this!

when I was flying my nextar I had a few problems with the tank, having the wrong lines hooked up was one,also making sure the rubber bung was tight enough to seal the tank so there is no air leaks.
if you suspect air getting into the tank, a good way to check for leaks is submerge the tank in water and while plugging the extra lines, blow into one of em(some clean longer tubing works well so you can see if there is any bubbles).
another thing could also be the carb seal a small tear in the rubber can allow air to get in, hard to tell my FXi runs well years later but I haven't taken it apart since I have owned it.

Look at the attached diagram and it should explain how the lines should be connected. But brief, here it is:
The line with the clunk is the fuel pick up and should be connected to the fuel input on the carburetor
The line that points the to top of the tank is the vent/pressure line and should be connected to the pressure nipple on the muffler
The line that points to the bottom of the tank is the fill/drain line and should be plugged tightely when the plane is running.

Hope this helps

Ken
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The diagram is a great example. As far as I can tell, All the lines are pointed correctly. I did put all new lines on the plane to no avail. Could there be any leaks from the engine that could case this? Crank Shaft or the bottom of the engine area.

I do have a new fuel tank with lines already in them and may use it and see how it works.

I also took the engine to the hobby shop and they said it had great compression and the piston looked fine.

Those .46 FXi engines are just about bulletproof, it's not likely the source of any airleaks or carborator issues unless it's been crashed into a paved runway.

Try richening up the high speed. Sounds like it could be running lean in the air and getting to hot.

My Nexstar came with the lines hooked up wrong.

I think the fuel getting sucked back into the tank is pretty normal. You get pressure from the exhaust into the tank, which forces fuel out of the tank toward the engine. When you shut it down, pressure wants to escape, and since you have a good seal in your engine, it escapes out the muffler, which I imagine is causing a low pressure zone, and therefore everything is getting sucked that way.

I agree that it sounds like you're running lean. Do you have the right fuel (18% lubrication at least)? Do you know about the pinch test? Pinch the line to the carb for a fraction of a second when the engine is running full tilt, and you should hear a spike (increase) in RPM's. If you don't, you're too lean and need to turn the needle valve counter clockwise.

Good luck.

I appreciate everyones comments and suggestions, I will be out this 4th of july weekend and when I come back, I will give everyones suggestions a try. I will post my results.

Thank You

My first thought was too lean as well.

I've had a problem like this when I got a small piece of junk in the fuel line. At idle, it would run fine, and run up to full throttle, but then very quickly cut out. I cleaned and blew out both the remote needle valve, and the inlet at the carb, and it worked just fine after.

My theory was that after the engine died, the junk would fall back out of the needle valve, and at the lower pressures around idle, would stay out. But as soon as I throttled up, it would get sucked back into place and block the fuel line, and the engine would quit again. I run fuel filters on most of my planes now, and haven't had it happen in a long while.

So it sounds to me that your engine is leaning out. there are a few tricks that you can do to see if that is the case but i am sure that you already know them. One thing that I havent seen anyone mention is the needle valve. where the valve goes into the housing there is a O ring in there, sometimes when you rev it up the air presure will escape from this o oring. I know it sounds crazy but there is a really simple fix for this, take a small piece of fuel tubing, not the standard blue line (I use yellow) and remove the neelde valve. then reinstall with the fuel tube on the outside of the valve and the housing, its going to take some convincing to make go back toghter. Again I know it sounds stupid but my engine on one of my planes was doing the exact same thing. there was no fuel leaking out of the needle valve so I, like you was also stumped until an old friend showed me this trick........... it works. good luck bud

I may be misunderstanding you. Your line in blue, The Carb line with the clunk is the middle outlet in the stopper. The top outlet is the vent and the bottom outlet is the fill line. I'm not sure if your saying the line with the clunk is at the bottom. Again I may be misunderstanding you. Good luck.

Nobody has addressed this point yet. If you only flew a few times, then put it away, and tried to fly a few more times, there is a distinct possibility your fuel has gone bad. I've had this happen to me. Try some new fuel.

You make no mention of your efforts to tune the engine. More than one RTF trainer has been sent out with insufficient travel on the limiters to be able to correctly tune the engine. I believe the Nexstar select falls into this category as well. Get rid of the limiters and get someone with some experience to help you tune the engine.

Brad

On my Nexstar they got the colors wrong, so just compare these pics.