It won't idle correctly. When I pull the glow ignitor from the plug, the engine immediately dies. After replacing the plug and putzing with the idle adjustment, we got it to run at about 1/3 throttle without dying after pulling off the glow ignitor. But whenI throttle down to idle, it dies. I had 4 guys from the club helping with the idle adustment and we couldn't get it to work. It runs fine on the high speed.I did notice some air bubbles in the fuel line between the remote needle and the carb. So I've pulled the tank and replaced the tubing. I'm not sure what to do next now.

What doesn't make any sense is the engine has been running just fine since January. Then suddenly Ican't get it to run reliably at all. I'm about ready to just buy a different engine.

Check your low end needle valve.  Sounds like your too lean at idle.

Since you have had help on it and have checked most everything but still see air bubbles it has to be an air leak someplace. Possibly the o-ring at carb or at needle valve. Another thought is the fuel line inside the tank.

For an engine that ran great to just stop, sounds like a piece of crud in the needle. Pull the needle assembly, and flush.

Yep, sounds like trash is causing the problem.

glow plug may need replaceing? i would try that first, then flush the carb.

Thanks for the responses. I've tried two new glow plugs including one that has an idle bar. Nothing seems to work. Called my LHS and they think the low idle is set too lean. I've already pulled the carb barrel and replaced the HS needle and am still getting the same issue.

I know everyone says OS engines are the best and all. But in reality, I'm learning every engine will have its issues. Now that I'm getting a taste of engine issues, it's making me less hesitant to try out a Super Tigre.

If you want to try a differant brand then give Thunder Tiger a try. They are right at the top of the food chain and half the price of the O.S.

Flush the carburator with straight fuel through the fuiel line with the needle valve removed.  reset the highspeed needle and the mixture valve to factory defaults.  If you do not start adjusting the mixture valve from the default position you will never get the engine to run properly in all operating speeds.  you can have an engine run great with the mixture valve improperly set by having the needle set to work well at that one speed but as soon as you transition from that speed the engine will run like crap or die

Hi DenverJayhawk
I have three OS 46FX engines, about 8-10 years old. Recently one of them gave me the same type of trouble you are seeing. Then I noticed that the low speed needle valve, LSNV, seemed to have little resistance when turned. It was actually turning by itself when the engine was running. I replaced the LSNV and the HSNV with a set from a near new OS 46AX and all is perfect now. The engine starts instantly, accelerates very good, and has plenty of power. The engine still has good compression. I inspected the O-rings on the old LSNV and HSNV and they were in very bad shape. The one on the LSNV fell apart. I also felt grit on the LSNV. My new procedure now is to periodically flush out the cavity that the LSNV is adjusted through, with a squirt of fuel. I will also replace the LSNV and HSNV O-rings if there is little resistance when rotating them. Just ordered one set of O-rings from Tower Hobbies.

This engine is 10 yrs old but w low run time on it. It probably has a max of two gallons through it. I no longer have the instructions for factory settings on the High Speed and Low Speed needle valves. Do you know where I can find them?

Like Villa Ikeep a couple of sets of gaskets and O-rings on hand for different engines. OS is a great engine but nothing lasts forever and parts do wear out or harden. Your problem sounds more like crud but if you see bubbles there is also another problem someplace. It's something simple but you have to work at it to track it down.

The engine has a brand new HSNV and o ring, but the LSNV is original. Actually, the LSNV is really just a screw and not really a needle valve. I didn't see an O ring on it when I took it apart yesterday. I'll have to look again.

Here you go

http://manuals.hobbico.com/osm/50sx-...1fx-manual.pdf

Ken

Thank you, Ken. As always, much appreciated. I might just actually get this stupid thing working again.

Denver,
 you are more than welcome. Try what others have said above about flushing out the high speed needle. Remove the needle completely, close the carb, connect your fuel pump to the fuel inlet, and pump some fuel through it. This will flush out any junk in their. From what you're saying this is where I would lay my money at being your problem.

Ken</p>

Hi DenverJayhawk
If you saw no O-ring on the LSNV then you have found the problem. It is not a plain screw. It has flat screw head, then some machine threads, then a goove for the O-ring, then a long small diameter end at the needel end that actually enters the tube that the fuel comes out of inside the carburator throat. You can probably find the manual by Googling for it.

any engine when not set up right and dirty will not run right, no matter what no matter what brand it is.

that missing o-ring is defintely going to let in air and not idle right

Pull the tank, clean it, change the fuel lines, pull the carb and clean it, that requires pulling it and tearing it down. When ever I pull a motor I tear the whole thing down but thats just me. since I'm messin with it anyway I like to see the piston liner and crankshaft/bearing condidtion. I've had just as much problems with super tigers as thunder tigers and tower and OS engines.

Get some red rtv. OS usually don't need it, except the LA's but if it' giving a problem then do it.

Put some RTV on the carb to crankase attach point and back plate lip and muffler. put some moly grease around the high and low end needles, don't get it on the needle, just the threads and o-rings.

Once you clean it and find and fix the air leaks. set the needles to factory starting point. My FX's I open the high end 2.5 turns and the low end even with the barrel and turn in one turn.

One thing no one has touched, How old is the motor? Anew FX is not going to idle until you run at least a half gallon though it, they'er just too tight.

Get it going and open to full throttle and set the high end. Lean to peak rpm then richen till you hear an RPM drop.



lower to idle. if it dies add a couple clicks of throttle and get i going. I like to pinch the test to get the low end close. Pitch the fuel line. If it speeds up and dies, th low end is rich, lean he low end. If it just dies, it's lean richen it. Go in 1/4 turn invervals. Reset the high end.
set the low end, try lowering the idle and repinch it. It should run 3-5 seconds with a good pinch. At this point the low end is close. Advance to full, it should hesitate or die, if it does you'll have to play with it 1/2 turn either way to get a good idle and instant trasistion. just remeber this point and nudge it either way until it coperates, it takes time to get it right.

Just get rid of it, I'll pay for the shipping to my house and then you can get you a new one.[sm=thumbup.gif]

This may be a dumb response but have you tried diffrent fuel, it could be bad. I built a skybolt arf and during the build I bought a new jug of fuel and used it the first time I flew it. I had engine trouble from day one. It was a Saito .91 from another plane and I knew it ran perfect. The fuel was getting worse each time I flew but, it was a new jug so I never thought fuel I kept trying to adjust the engine. One day it would not run at all so I had brought another plane and I fueled it up. That engine did the same thing (BINGO) I found the problem. I happened to have bought a new jug that morning and I put that in the second plane and it ran fine. I fueled up the skybolt and it's been running fine ever since.

ok, so I've pulled the carb and cleaned it. I also flushed the HSNV and pulled the carb barrel and LSNV idle needle to inspect and clean. There is an intact o-ring on the LSNV that looks to be in good shape.