cap 580 dan

Okay so I built a eagle 580 with a os 61 engine, its side mounted. It also has the old 7m carb, this is an old engine but ran great 3 years ago.

So I go to start it and its running lean, and dies when you throttle back, I notice the engine shuts off, the fuel thats in the line goes back into the tank, is this normal?
I am thinking tank setup is bad, but I dont know. Any ideas will help.

1QwkSport2.5r

Whenever you have a misbehaving engine, put it on a test stand with a known good fuel system and run the engine. If it runs okay on the test stand then you know something is amiss in the aircraft. The fuel should not go back to the tank unless the tank is too low or there's a leak in the fuel system. I'd be using a test stand and nail the engine down to be 100% before doing anything else personally.

cap 580 dan

I agree, but thats alot of work might as well do it though

1QwkSport2.5r

Sure beats risking bringing your plane home in a hundred pieces, eh?

cap 580 dan

whaacha think, the line to the carb is comming from the bottom right tube. it is maybe 3/4 of an inch below the carb..

1QwkSport2.5r

That's likely not a major issue. I'd still pull it out of the plane.

JollyPopper

My Feedback: (6)

It appears you have an OS .61FSR engine which some folks believe was the best engine OS ever produced. Most came with a 7D carb which was also used on the 90 and 1.08 engines, and to get it to work better on the ;61, OS offered a brass insert to slip down into the bore of the carb throat restricting the bore of the carb and forcing the engine to draw fuel better. I'm not sure 7M carbs used these inserts but you might look into the carb and see if it has a brass insert in it. If not, you might try one and see how it works. Another problem could be the small o'ring on the needle. You say this engine sat for a couple years and that little o'ring could be passing air. The fact that the fuel tends to run back into the tank suggests a possible air leak somewhere. Also check the nipple on the muffler. If it is clogged with congealed oil it can cause all kinds of silly things. If none of these are the problem, check for a cracked fuel line, possibly inside the tank. A cracked fuel line on the supply line to the carb could also cause the problem. Also, does the fill line with the fuel dot on it have a clunk on it as well as the carb supply line? You definitely have a fuel supply problem and any or all of these things can contribute to that kind of problem. The .61 FSRs are a sweet running power plant when everything is right in them.

cap 580 dan

Yeah man the fuel fill line has a clunk too, problem?
Everything is new so i doubt cracked lines the case.
And youre telling me, when this engine runs good its a bat outa hell. its 35 is not 40 years old!!!.
the cap 580 instructions said to use a clunk line of fuel fill. which i thought was odd. is that the issue here? If so i a, curious on why

Mr Cox

Are you using the same type/blend of fuel as 3-years ago?
Have you tried to simply set the low end a little richer?

cap 580 dan

Its all new fuel tubing, will the extra cllunk in the tank cause issues.
and I have not I dont know whats what on this carb i know it ran perfect a wile back with no issues

cap 580 dan

Oh and yeah i am using 15% cool power its new aswell.

1QwkSport2.5r

If using a 3-line setup with two clunks, you may encounter issues. I did when I tried it with an ST S90. When coming off the throttle from WOT the pressure line would fill with fuel and the engine would go rich and quit. I didn't have much success in using a 3-line setup where others had success with it. I went back to using a standard pressure line inside the tank (pressure line came in above the fuel level) and my problem went away. Some exhaust systems don't bleed the pressure off quick enough when coming off the throttle in my experience.

cap 580 dan

I think thats my problem. I have a tank from an ugly stick, that ran this engine perfect might fit it in.

1QwkSport2.5r

Anytime I have an engine that is normally reliable and runs well and all of the sudden doesn't run properly in a different craft, 99% of the time the fuel system is to blame. That's why I suggested the test stand with a known good fuel tank/system to eliminate all variables to determine if it's the engine or the fuel system. I had to do this with a TT .46 where on one craft it ran like a Swiss watch and in another it wouldn't throttle or idle worth beans. WOT great, anything less and it would quit. On the test stand it ran like a Swiss watch again. Changed the fuel tank and all was well again.

cap 580 dan

I have the tank out looking into it now, I have some spare tanks so well see

flycatch

My Feedback: (26)

Your problem is called "vapor lock".

cap 580 dan

That isnt the problem, I used to fly rc helis professionally I know the engines are not much different, But i was king at tuning and troubleshooting the heli stuff,
Its not vapor lock,

Now I did some thinking, gravity is a ***** we all can agree. This planes a tail dragger. i make the plane level and the fuel doesnt go back into the tank.
I dont know if this is normal but I didnt even think about gravity being the problem, I tried a different tank and it did the same thing.
What I am doing is priming it, and seeing if the fuel goes into the tank, I tried that on both tanks and same thing. I think the tune of the engines just off, IE the idle mix.
Now this 7m carb I know really nothing about any insight would be nice

JollyPopper

My Feedback: (6)

Since the problem goes away when the tail is raised, it sounds as if the engine isn't drawing fuel up that short distance between the fuel feed line and the center of the carb. The tank appears to be about 1/2 inch below the needle valve. The pressure from the muffler produces a bit of boost for the fuel draw, but the primary force is vacuum produced by the engine. When the piston comes down (the downstroke), it produces a vacuum between the top of the piston and the head, That vacuum draws fuel through the intake ports of the sleeve much like drawing soda through a straw. If this is a ringed version of the .61FSR, the ring could be gummed up from sitting, reducing the vacuum produced on the downstroke of the engine. If that's the case, it will clear up by simply running the engine.

cap 580 dan

Agreed, the slime on the bottom of the plane, is a light colored brown. ill just run it and see if it gets better.

flycatch

My Feedback: (26)

http://www.rcgroups.com/forums/showthread.php?t=138519 Read this.

cap 580 dan

Good thread, honestly im going to change the plug, set the needles and see what happens

Mr Cox

I take it you haven't touched the carb settings at all?

The needles are there to be adjusted on, there are so many things that affect the fuel delivery that you of course have to optimise the carburetor settings for every installation, prop choice and fuel etc.

By using an extra clunk you reduce the pressure at the fuel pickup when the tank is full (compared to a regular set-up). But the advantage is that the pressure is now independent on the fuel level, as opposed to the regular installation where the pressure drops as the level drops in the tank.
So put in a new glow plug and tune the carb with the second clunk installed, it is as easy as that. For a description of the carburator you can have a look here; http://manuals.hobbico.com/osm/27481000-manual.pdf

Bozarth

My Feedback: (15)

All this fuss...run it rich.

Kurt

cap 580 dan

I am pretty sure i figured it out,first off i fired it up and it was running decently. if i back off on throttle sometimes itll die though. But i got to looking and noticed some slime around the muffler. my old man i guess like 10 years ago tapped into the muffler for smoke, and theres just a bare hole there now LLOL. is this this issue? i think yes

drac1

My Feedback: (4)

Internal combustion engines do not suck the air/fuel mixture into the engine. Atmospheric pressure does this by displacement. As the piston travels down, space is created which is then filled by the air which enters the cylinder through the carb opening. ie -atmospheric pressure displacing air from outside the engine to fill the space created inside the cylinder. (equalisation).
While the fuel is sucked in a little by the high speed air going past the spray bar, it is not enough for the engine to run properly. That is why we use muffler or crankcase pressure on unpumped engines. To force the fuel into the carby.