OK GUY'S, I need some help!!!!

I have a OS 46 FX that is mounted on a Model Tech Magic Extra 300 (great flying plane, poorly built plane, but that is another thread). I put this plane together in the fall, and the following is the things I think I did right and things I did wrong.

What I think is right:

1 - Break in engine with stock muffler exactly like the book.
2 - Use Cool Power 15/16 and boost the oil to 18% with an additive.
3 - This may be good or bad depending on who you talk to
I have a tendency to run all my engines rich!!

What I might have done wrong:

1 - Put a Mac muffler on the plane right after break-in.
2 - I could not get enough back pressure off the Mac muffler, and run the engine pretty lean. Quit a couple of times in flight. I took the Mac tuned pipe off and put stock muffler back on.

My problem is I have been fighting to try to tune the engine ever since. Each week I have to retune the engine, and for example I flew today the first four flight run great, then suddenly on the fifth flight it was too lean. Landed and richened it one click everything was fine. It seems to air temperature and humidity might have a effect, but I have a fellow member with the same OS 46FX with a Mac tuned pipe on a Somethin Extra and never touches the needle valve and it screams.

I also have the following OS engines on other planes and I have no problems with these, OS91FX, OS61FX, and two OS 91 four strokes.

Any opinions would be greatly appreciated!!

Thanks,

Jimmy

check plug and for air leaks there is not much else to check and foaming of fuel in tank from viberation????frank

Replaced fuel lines & pressure. Using a known good tank,
No air bubbles in fuel lines????????????

Should I change the needle valve? Or at least the O-rings. I put a clear line from the needle valve to the carb "No bubbles"

Got a piece of "gunk" caught at the needlevalve acting like a "check valve", resulting in occasional leaning ?

Pull the head off and wipe the inside of the liner with a clean rag to check for peeling of the nickel plating. If you can see any brass whee nickel once was then that might explain your problems. If it doesn't then perhaps your needle is changing in flight at certain rpm/vibration levels - check to see that the spring steel clip has plenty of pressure on the nedle valve and clicks with authority.

If one click is solving your problems then I think you still might be too lean. Richen it up 3-4 clcks at least.

It has been my experience that the OS motors are more dependent on back pressure and sometimes after market mufflers do not supply enough to the tank. I've solved the problem on a couple of planes by plugging one of the two pipes on a pitt's style muffler. I've even seen people have problems with the 46 fX by removing the internal baffle in the muffler.

You may have damaged the engine due to a lean run.

Make sure the tank is well isolated from the fuse. may not show foaming on the ground but when the prop unloads in the air. Foaming at higher frequency than you would get on the ground. One way to find out is to put on a smaller prop to make it rev higher on the ground just for a test.

Thanks to everybody for all the help!!!

I am not to the point of dismantling the engine YET!!!

Unfortunally, the Model Tech Magic 300 does not leave you much room for isolation of the fuel tank, you do what you can do. But I think if that was the problem I would have seen some threads with the same problem.

The needle valve and the fuel system, I have been through with a fine tooth comb. Replaced everything except the needle valve.

I tend to believe I screwed the engine after break-in with the Mac Tuned pipe and running it too lean, but it seems like on the warmer day's I have no problem with it.

I will carry on until spring, but if anybody comes up with some idea's they would be greatly appreciated!!!!

Thanks,

Jimmy

my 61 FX used to quit all the time while it was brand new. The 61 FX is similar to the 46 FX only larger disp.

I broke it in per booklet, 2 tanks or so. Used Bisson pitts muffler.

What happened was during break-in and shortly after, it needed a lot of backpressure which the pitts did not supply.

I also had an in-line fuel filter.

The engine would start and run but would not hold idle. Then it would quit in the air.

I plugged one of the two pitts exhaust tubes and removed the inline filter (dubro).

The engine ran fine then, didnt quit and held idle.

After 10-20 flights the pitts restrictor i put in (1/4-20 set screw) fell out in flight.

Then engine liked the lesser restriction and was fully broken in, at least enough so that it ran like a champ ever since. This engine is the best I've ever owned.

Not sure if the problem would have even occurred had i started with the stock muffler, but the engine was broken in as i was planning to run - - with pitts.

It has to be pressure in the tank. The muffler you have does not supply enough pressure in the tank. I had exactly the same problem with my OS 46 FX when I tried Tower Tunned Muffler. It was working very stable on the ground, but it's quit after 30 seconds in the air. This is the only one problem I had with my OS

I've been running a mac's muffler on my 46fx for a couple of years with no problems ever with fuel draw or pressure, I think you have some blockage in the carb/ needle valve area ??

Just my $.02, hope you get it figured out soon.

Hi!
Well if you have problem with your present tank why not get a Tettra "bubbleless tank" from Dave Shadel (US YS importer)
These Tettra tanks are used by every pylonracer in the world and give much better reliability than ordinary Du-Bro or Sullivan fueltanks.
Tank size is vital...240cc -300cc (8-10oz) is what you should use. Not bigger!
Always mount the tank so the centerline is horizontal with the carb needle.
Use as short fuellines as possibly!
Plug: OS 8 or Enya 3, and never ever reuse an old glowplug washer!
Always put in a new washer when you change glowplug.
Never use more than 15% nitro!
Also check all bolts and retighten if necessary.
Prop is also vital...APC is what I recommend, size is up to you. Anything from a 8x6 to a 12,25x3,75, will work depending on the airplane.
Most of the time a 10x7or a 11x6 will work best in ordinary sportairplanes (if you fly at sea level).
Never use a cheap plastic spinner!
Always balance your props and balance them by sanding on the heavy blade (on the front sidewith the airfoilshape).
You could also paint the tips white if that helps balancing (it also helps visibilitiy).

Regards!
Jan K
Sweden

Jan K,

hi to sweden, liked your post, this sounds like very good advice but have a few questions -

you sound like you have experience with these things. i am going to ask "why" on almost all of them@! I am not being sarcastic at all, i want to learn more is all.


> Tank size is vital...240cc -300cc (8-10oz) is what you should
> use. Not bigger!

why, does the engine care how big the tank is?

> Always mount the tank so the centerline is horizontal with the
> carb needle.

agree good for fuel flow at any attitude.

> Use as short fuellines as possibly!

agree, best to reduce fluid drag in lines. what is your opinion on using an in-line fuel filter? YS practically insists on it.

> never ever reuse an old glowplug washer!
> Always put in a new washer when you change glowplug.

why is this? I am sure I may have re-used old washer and wasn't concerned, but since you stress it so much what is the reason?

possibly a bad seat / seal when the washer is compressed multiple times?

> Never use more than 15% nitro!

I have an OS46 FX and a YS45 FS. The YS recommends 20 nitro, the OS - not sure on the recommended but I think 10-20 should be an ok range.

What is your concern here, overheating of the OS at higher nitro content?

> Also check all bolts and retighten if necessary.

any leaks or compression problems may affect engine performance and idle.

> Prop is also vital...APC is what I recommend, size is up to you.

I agree, i used to use MA props, the standard ones, and then switched to all wood, wood was better but got expensive when they break, and now APC is my prop of choice - excellent prop design with minimal high-rev distortion compared to MA (not scimitar. Scimitar seems comparable to APC)


> Never use a cheap plastic spinner!

OK I use dubro spinners and no problems, what is your experience, did you have one break? I have never seen one break simply due to engine rpm.

Hi!
Well I dont want to sound like a "Mister Know it all " but I used the letter ! as a way of saying that: this is very impotant.

Yes tank size does matter. To large a tank means to high fuelpressure and this most engines could not cope with.
You will notice it when the engine could not hold it's needle setting from start to finnish and you have to set the highspeed needle a little rich at the start so that the engine would not go lean at the end of the flight.

Buy mounting the fueltank so that the centerline is horizontal with or slightly below the carbneedle orrifice inside the drum of the carb, one has a set-up that enables the engine to suck fuel without being subjected to too much variations in fuelheight (fuelpressure). Also by doing this one can also fly inverted
without having the engine go rich (or lean).

I don't use a fuelline filter on the engine. I use a large filter in my toolbox.

When I was on the Swedish pylonracing team in -95 at the World Champs in Muncie, Dave Shadel former World champ in pylonracing told me to never ever use a used washer because they can leak!

Most sport engines doesn't like more than 0-15% nitro as the nitro content raises the compressionlevel inside the engine.
Of course you could use more nitro but more than 15% usualy means that you have to lower the compression ratio by adding another head (0,1mm)shim.
More than 15% will only produce more heat and a finnaly distroy the engine engine.
I myself would never use more than 5-10% nitro in an OS.40-.90.
There is no reason doing that.

Well nylonspinner could of course be used and I use them sometimes myself on not so fast airplanes with small engines. But on larger (.40 or larger) I prefere Tru-Turn aluminum spinners or just a aluminum spinner nut!


Regards!
Jan K
Sweden

Here is an easy thing to check, it happened to me once and I thought the engine was going crazy after being real stable. Check to see if the needle vavle turns too easily if so it might just be turning from vibration. just remove the valve and bend that little tab (the one that makes the click noise) in a little and then screw the needle valve back in. Hope this makes sense, I know it seems very basic and don't want to insult you if you already thought of this. Good luck

My OS .46 FX ran great for about 3 months and then started to act like yours..... I had air bubbles between needle valve and carb.... I started by replacing the small nipple fittings on needle valve and carb, still had bubbles. Replaced the O-ring on the needle valve, still had bubbles. Ended up cutting/machining the needle valve off the crank case and replaced it with a tower hobbies .46 needle valve - double O-ring type. No more bubbles and engine has run great since. I myself run Powermaster 20 or 30 % (after break-in) with no problems as of yet..... Not saying its the best for the engine rather just tired of having multiple fuel jugs all the time. I do ensure its just a tad rich though.

Smitty