Hey all,

Sun_Kissed_Girl gave me her nexstar to tune for tomorrow...I'm having a little trouble with it. The engine is the stock OS .46 FXi...I can get it to run, but when I slam on full power, it skipps and coughs a little before revving to full. After going back down to idle, it idles really fast then slowly looses RPMs until it eventually stops...any help, please? The LSN is in the stock position, and the HSN is about an amazing 5/8 turns out! Any more richer, and it won't start or run.

Lean the low end. Small increments and test.

k thanks...and also, the exahust that comes out isn't blue-white, but more brown-black...and the sludge on the side of the airplane is brown-black...is that normal?

Depending on the fuel your running. Sounds like Omega or something with Castor. I run cool power its got synthetic oil, no where near the mess.

Yeah, its Omega 10%...but what I find funny is that my .61FX and my .46 AX both produce blue-white smoke with Omega 10% but this OS .46 FXi produces brown smoke...

As far as I know (I think), that engine has a black plastic "limiter" on the high end speed needle. Remove that part.
Now start the engine again, SLOWLY rev up to full throttle and adjust the high end needle for optimum speed, then back off 250 rpm (if you have an rpm meter), or three clicks. Lower the throttle and then SLOWLY rev up again.
Will the engine idle OK and then come up to speed OK ? If satisfied, put engine from full throttle, back to idle. Now quickly rev up to half speed (goose it). Does the engine rev OK, without hick-ups ? If yes, you're done, if not, you have to adjust the low end speed needle (the one inside the throttle arm). Adjust in VERY SMALL increments, until the engine will smoothly rev up without hesitations. When satisfied, one more last check. Slowly rev up, then lower back to idle. Pick up the plane and hold the nose up 20 degrees and then lower the nose 20 degrees. The engine should not die on you. If it does, the low end needle is still not at optimimum. Continue until all parts of the tests are satisfactory.

HTH.

I agree with 'cuda. Those are symptoms of a rich low-end. The O.S. uses an air bleed, I believe. The air hole in the carb should be about half-open. If it's closed or nearly closed, back out the screw until it's about half-way open. Then back out the high-speed needle about three turns, and start from there. If the O.S. doesn't use an air-bleed, never mind.

The OS 46 FXi has a twin needle carb

If the problem remains not tuneable. Go search the engine forum on this engine. I read where some had machining metal left in needle area where it has caused your problem as stated. They just tore it down an flushed, this is where they found fragments. It solved their problem of untune ablity, set rich go lean, thierfore brown caster. Note if fragments are causing lean your very lucky your using caster,last defense on over heating.
Just a thought Rich

Just turn the low end 1/8 of a turn at a time clock wise, open the throttle all the way so you don't bottom it out and give it a shot. Don't try to adjust the low end with the engine running unless you own stock in suture material.

I actually noticed with my nexstar, whenever i run it, it always produces a brown black sludge on the side of the plane. My engine runs great, but i have now tried 3 different types of fuel and the result was the same every time. Also when I turn the engine off and tilt the plane backwords a greenish-blue substance come out of the back of the plane, should I be worried about something?

Sounds like the bearings are stuffed and just grinding out the exahust, probs from running to lean b4 you got it.

Before you start thinking that something's wrong with your engine, collect some of the exhaust residue on a piece of white card stock. The oil will be absorbed into the card and any solids will remain on the surface. If you see metal particles, then you have a problem. Most of the time, though, you have nothing left but a few carbon particles and a stained piece of card.

Model fuels will discolor greatly in the muffler. The muffler will retain some heat and 'cook' the fuel residue before it's expelled. This is the dark smudge that gets all over the model. Fuel residue isn't going to be colorless. After a flight, there will always be residue in the muffler that can be poured-out. There will also be raw fuel left in the crankcase. That's why you should disconnect the fuel line from the engine and start it over and over at the end of the day until it will no longer fire and run...you've just burned-off any fuel remaining in the engine.

From all the notes, the engine sounds like it's just not guned correctly. The high-speed needle should be leaned to just rich of peak RPM, and then the idle should be adjusted. The idle mixture sounds to be quite a bit rich. Once the carb's balanced, it will only need the high-speed needle checked at the start of each flying day.

Sorry I haven't been able to reply, guys. Between high school (which is becoming a royal PITA), and shopping for a T-Maxx, there isn't much spare time anymore. I'll try all the procedures you guys posted Saturday probably.

Yeah, definately start with the low end needle. I had the EXACT same problem with my Nexstar - I just leaned the low end a bit and it ran absolutely perfect. I also run Omega 10% and yes, the exaust gunk is brownish. Good luck.