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OS 0.25 FP engine running problems

Old 08-23-2006, 11:41 PM
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tonytheshovel
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Default OS 0.25 FP engine running problems

I have an OS 0.25 in one of my planes, and I'm having a lot of problems getting it to run properly. I'll tell you the story of what I've done and then maybe you can help? I bought and installed the engine about 7 years ago and flew the plane about 4-5 times. The engine then sat in the plane just as I left it for 7 years. About a week ago I decided to take up the hobby again and took the engine out of the plane to clean it up, the little barrel in the carburetor that adjusts the throttle was stuck, so I soaked the whole engine in glow engine fuel over night and everything seemed to be moving as it should. I installed a new glow plug and put some of my 7 year fuel in and it started and ran well on the first spin. I took it out to the field and flew it, the first flight was good, engine ran great, but after refueling it I tried starting it again and I couldn't get it running as nice as it was. In fact after that first great flight I haven't been able to get the engine to run for entire flight, sometimes it would quit half way through the tank and sometimes it would barely take off before it quit, but never again could I get to run as well as the first time. I thought it might be any one of the following problems,

- the 7 year old fuel (I later realized it was 25% nitro I use to use in my helicopter)
- dirt got into the carburetor on the first flight
- unbalanced prop do to the nicks from some rough landings
- air leak in the fuel system

So I bought a fresh jug of 10% nitro/18% oil fuel, a new glow plug, and I took apart the carb and cleaned it out well with some fuel, and replaced the propeller, and replaced all the fuel tubing. Now I can't even get the thing to start! It seems to start sometimes when the throttle is set to approximately 1/2 or higher but then dies when it is lowered below 1/2 throttle, and when it does start full throttle seems to be solid. I tried messing around with the two screws on the carburetor but it just seem to make things worse, I just couldn't get them both in the correct position for the engine to start and run at idle. In my engine instructions it says one screw is the air bleed screw, and one is called the rotor guide screw. Is there any logic way to adjust these two screws instead of just randomly changing them until something actually works? I'm assuming these screw settings are the problem, but maybe I'm missing something. My glow battery is good, the glow plug glows bright orange. Please help.
Old 08-24-2006, 10:56 AM
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Bax
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Default RE: OS 0.25 FP engine running problems

The "rotor guide screw" is used to adjust how far the throttle closes, and it also keeps the rotor in the carb. Set it so that the carb closes down to about 1/16" or a hair smaller.

Set the air-bleed screw so that it blocks the air-bleed hole by 1/2, or a little more open. It adjusts the idle mixture. Turn clockwise to richen the idle, counter-clockwise to lean the idle.

Start out with the high-speed needle at about 2-1/2 turns out from closed. That's a rich setting. Open the throttle to full, Choke the engine. Flip it briskly several times with the batter NOT attached. Close the throttle to about 1/2-open, attach the battery and crank the engine. It should start, if it's not flooded or too dry of fuel (the brisk flipping tends to prevent flooding). Once it starts, leave the battery attached and advance the throttle to full. The engine should accept that. Now you can work with the high-speed needle to lean the engine a bit until it's running smoothly. Remove the battery clip from the glow plug. If the engine has been run enough, you can lean the high-speed needle until the engine's running just rich of peak RPM.

You should then be able to retard the throttle a bit at a time and work with the air-bleed screw to get the idle mixture adjusted.
Old 08-24-2006, 01:54 PM
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tonytheshovel
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Default RE: OS 0.25 FP engine running problems

thanks for the quick response, that's great. Just one more quick question, adjusting the air bleed is very small adjustment then, on the order of a 1/8th of a turn at a time? I assume this because I was turning it 1/2 and full turns and it was not improving the idle running, so maybe my adjustments were just to big?

A couple other things to add, the engine is mounted inverted, it is like this by design, it's actually mounted in an old Livewire Champion. Does mounting the engine inverted affect starting and running? If so in what way in terms of ease of starting and reliability in the air? I notice it tends to flood the glow plug and I have to take it out quite often to clean out the excess fuel, I assume this is a result of the inverted mounting. I also find that the glow plugs have been turning quite black over and around the idle bar, is this normal?

thanks again for the quick response, I will try the engine again tonight or tomorrow.
Old 08-25-2006, 01:12 PM
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Bax
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Default RE: OS 0.25 FP engine running problems

Adjusting the air-bleed screw in small increments is best. That way, you don't "blow through" the correct setting.

Inverted running can be problematic for many, many engines, not just the FP-series, though engines with air-bleed carbs can have more difficulties.

The main problem is that the glow plug becomes the lowest point in the fuel system, and can act as a sump and collect fuel at low RPM. This tends to "put out the fire". Some engines will idle inverted, but don't accelerate well, if at all. There are a few things you can do:...1) lower the fuel tank to the bottom of the allowable range (centerline about 3/8" lower than the carb center), 2) tilt the engine slightly off vertical, 3) add an on-board glow plug battery to keep the plug lit.

Do a search on inverted running and you'll that a lot of people have problematic engines when mounted inverted.

For easy starting, you can flip the airplane over, put it on a stand, and get the engine started. Many engines, once started, will run happily inverted.

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