OS .46 FX Idle/Run Problem
Duane Lupia
I seen you havent tried new fuel. Pick up some 10% morgans pink fuel.
Castor synthetic blend. Sounds to me like your getting a hot engine. Also
it shows that you have not tried raising or lowering your tank height in
your plane. Give it a try. I had a similar problem with a supertigre .51.
It was a tank height problem. Also pitch back on your prop. A 11x7 prop is
pretty heavy. Try a 11x5 or 10x7.
Thanks
Duane
Tom Johnson wrote:
> Attention Engine Miesters,
>
> I have a relatively new OS .46 FX that does not want to transition
> from idle to full power, always had this problem from the beginning.
> It has been properly broken in and has 20 to 30 flights on it. It is
> installed in a Sig LT-40. Prop is Master Airscrew 11" X 7". Fuel is
> Power Master 15% 2 Cycle. Glow plug is OS A3 (standard idle bar plug
> also tried). A base line adjustment of the idle needle valve was made
> according to the book: at just closed throttle - one turn open from
> the closed jet position. The engine was tuned to the usual full
> throttle *rich* position from peak RPM (both by ear and tachometer).
>
> The problem has been that no amount of adjustment of the secondary
> (idle) needle has produced a satisfactory transition from idle to full
> power. It goes from too rich to too lean, never hitting the sweet
> spot, no matter how minutely the screw is turned.
>
> Typical results after idle screw is set up according to the book and
> engine is tuned to peak usable RPM:
>
> 1. Too lean. Engine idles well, but dies when the throttle is opened.
> Dry exhaust.
> 2. Open screw slightly (1/10 turn or less) engine dies when the
> throttle is opened. No smoke.
>
> And so on, until:
>
> 3. Too rich. Engine idles well but sputters, surges, throws fuel
> before increasing in RPM.
> 4. Close screw slightly. Too rich. Engine idles well, transitions from
> low to high RPM fairly well, but *loads* up during long idle period,
> idle RPM begins to drop after a short time. Engine dies when throttle
> is opened.
> 5. Close screw slightly. Too lean. Idles well, but engine dies when
> throttle is opened. Dry exhaust.
>
> Remedies tried:
>
> 1. Replace A3 plug with Idle bar glow plug.
> 2. Remove carburetor, disassemble and clean.
> 3. Remove fuel filler valve and plumb fuel line directly to
> carburetor.
> 4. Inspect fuel filter screen for debris.
> 5. Pressure test tank and lines.
> 6. Vacuum test tank and lines.
> 7. Use different gallon/brand of fuel.
> 8. Reset idle speed higher.
> 9. Check all threaded fittings/screws for tightness.
> 10. Have club *expert* mechanics adjust/trouble shoot the problem.
> 11. Chicken entrails thrown onto a pentagram while hopping around on
> one foot. (both the left and right foot tried).
>
> When adjusted as close as I can get to the proper set up I have been
> able to fly this engine well. It will take off normally, if it makes
> it through the transition. I cut back to idle for landing and it will
> speed back up to taxi 90% of the time. If I try to make a touch and
> go, it will die 90% of the time. The problem seems to be loading up
> the engine during idle or getting it too lean and having it die when
> the throttle is opened. There is no middle ground.
>
> Anything I haven't tried?
>
> Tom
Gerrard Goodhind
Here are some more suggestions set thottle to low position i.e. air inlet
barely visible.
blow into engine feed line. Close (CW) slow running needle until there is
no air flow. Turn back CCW until air just starts to flow. That is the
starting point from which to tune the slow running. Any difficulty in
acheiving this look in the needle valve assembly and fuel inlet for
dirt/blockage. If the engine will not tick over / pick up you know you have
a route for fuel to the engine so all that is left is the air. Is the back
plate loose/leaking? is the carb assembly leak proof?
Still not working - last gasp posibilities. Slightly blocked clunk in tank,
fuel foaming. pressure line blockage, some OS engines had a problem in that
the pressure nipple was barely drilled through, take it out and ensure the
hole is completely clear. Replace fuel tube in case there is a pin hole or
split. Try and OS8 Plug. try running the engine without pressure ( the main
needle will need to be opened up). Thats it No more ideas.!
Gerrard
"Duane Lupia" <sho...@acronet.net> wrote in message
news:3BE96CE2...@acronet.net...
Tom Johnson
Since then the engine has been replaced with another new O.S. 46 FX.
The new-new one ran great right out of the box. The old-new one never
did work right, even when it was gone over by the local hobby shop's
technician. It still hesitates during transition and it does not
develop as much power as the new-new engine. It is especially
noticeable in climb out during take off. Being that one engine runs
fine when swapped on the model, it has to be the engine at fault. O.S.
should have it by now as the dealer sent it back. It will be up to
them to see if they can find the problem, if not I can live with the
engine if I install it on a smaller model that does not require the
full output of the .46.
Thanks for taking time to respond.
Tom