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evolution 61nt?????????

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Old 04-29-2008, 10:12 AM
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FA82Showtime
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Default evolution 61nt?????????

When i turn the prop with finger over carb, as it compresses the fuel draws to the carb, once it flips over the compressin state
the fuel quickly draws back to tank??? The plane is a tail drager, would the angle of the plane cause this. the motor runs until
you hold the plane up right andi got it set real rich and still will quit. Tank problem?
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Old 04-29-2008, 11:37 AM
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Default RE: evolution 61nt?????????

ORIGINAL: FA82Showtime

When i turn the prop with finger over carb, as it compresses the fuel draws to the carb, once it flips over the compressin state
the fuel quickly draws back to tank??? The plane is a tail drager, would the angle of the plane cause this. .....................
I wouldn't say that's a problem. When you put your finger over the carb and rotate the crank, the cylinder will and is supposed to draw air/fuel from the carb. With your finger over the carb, you seal the system and it draws a much higher vacuum. Since it can't draw air (finger blocks this) it pulls a ton of fuel through the only other escape, the fuel lines. As you rotate the crank further, the piston drops below the exhaust port and the vacuum you created is lost though the exhaust. No vacuum, no fuel draw, and you should be able to feel this with your finger too.

BTW: That's how we prime the engine with fuel at the start of a flying day.


All that said, it could still be a tank problem. I think I'd check the clunk first to see if it's installed properly. I nosed in once, and the clunk "flipped forward" in the tank and hung there. Cause all knds of weird problems.

I'd pull the pressure line from your muffler and blow through it, see if the system builds pressure and fuel moves to the carb.

I've got a .61NT and I'm trying to think what else..... Heck I've flown it without the pressure line before. It run a little lean, but really I couldn't tell that much. I guess it blew off, not sure how that happened.
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Old 04-29-2008, 11:48 AM
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Default RE: evolution 61nt?????????

Oh, for my info (and others) what fuel and plug are you using? I'd be interested to compare with my setup.
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Old 04-29-2008, 01:37 PM
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Default RE: evolution 61nt?????????

Assuming your tank is properly installed, and the vent is open, this is very normal if the prop is turned over slowly. It's a function of the intake timing. The timing is optimized for high-rpm running, and as such the intake rotary valve stays open beyond TDC, usually for 20-50 degrees (can't remember exactly what's typical). That means that if you rotate the engine slowly, first the engine will suck, then it will blow a bit from the carb. Some engines actually spit a bit of fuel from the carb at very low idle.

To prime the engine, flip it as quickly as if you were trying to hand-start it.

Some engines will also be nearly impossible to prime when hot, because as soon as some raw fuel hits the hot engine, it flashes to vapor and blows the fuel back to the tank, emptying the fuel line. My Norvel .061 is a great example of this, tho any hot engine may exhibit this.... 'course, there's not alot of reason to prime a hot engine anyway!

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Old 04-29-2008, 06:25 PM
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Default RE: evolution 61nt?????????

ya, i was just wondering if it was a tank problem, anyhow the fuel i use is omega 15% in most of my planes some power master also
the 61 has 12x6 APC prop and i use a O.S #8 plug
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Old 04-30-2008, 10:14 AM
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Default RE: evolution 61nt?????????


ORIGINAL: FA82Showtime

ya, i was just wondering if it was a tank problem, anyhow the fuel i use is omega 15% in most of my planes some power master also
the 61 has 12x6 APC prop and i use a O.S #8 plug
I use the same fuel. You might try a Hanger 9 Super plug. It's actually a 4-stroke plug. I saw a marked improvement over the OS#8. It costs more, like $8, but I haven't fouled one yet and I had my engine running stupid rich for a long time..... (Long story, but now I've got it tuned it properly.) When I was trying to iron out my engine issues, Horizon tech help told me the H9 SP was the way to go.

I don't think the plug has anything to do with your symptoms, but you might consider the plug when you get it all ironed out.
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Old 04-30-2008, 10:37 AM
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Default RE: evolution 61nt?????????

Another approach you can try for priming your engine (I use this one with the afore-mentioned hot engines), is to plug the exhaust with your finger and turn the engine over quickly, either by hand or with a starter. This will pressurize the tank and "blow" the fuel to the carburetor. If this works, you don't have any major tank issues, as this requires the pressure line, tank and supply line to be "tight". With this method, however, it is important to turn it over relatively quickly, with minimal time between revolutions. It will take a little longer than the carb choke method for fuel to get there.

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