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Model Forum / Radio Controlled / Air Models / August 2004newbie questions w/ OS .46FXi -- stalling out
I'm new to RC and need some help. I have the Hobbico NexStar w/ the OS .46FXi engine and have had much success, though lately I've been having a lot of problems with fuel delivery. I'm not sure what it may be, but I have replaced the fuel lines for good measure and confirmed there are no leaks in the tank or the lines and the tank holds pressure (even pressure tested it underwater!). Hobbico shipped the plane with the wrong needle in the needle valve housing. I replaced the housing, then realized it was the wrong needle and out of frustration bought a Fox aftermarket needle instead-- http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXG924&P=7 Questions: Can I remove the carburetor and low-end needle without damaging the o-rings? If not I don't want to remove them without replacements handy. What is a good starting point for the low-end mixture adjustment on the carb? How about on the remote needle? What would cause fuel to flow from the pressure hose INTO the muffler while the engine is running at low-to-mid throttle? This is only at certain RPMs. I noticed it while running the engine in the garage. It only happened twice. When it happened LOTS of fuel was being dumped out the muffler through the pressure tube unburned. Are plans / pics available to make myself an engine test stand? Thanks! -Steve in Phx. two_wheeled@hotmail.com Could it be that you got the pressure and carb lines reversed? Raw fuel shouldn't be able to get to the muffler through the pressure line unless the outlet inside the tank is very low. -- Paul McIntosh http://www.rc-bearings.com > I'm new to RC and need some help. I have the Hobbico NexStar w/ the OS > .46FXi engine and have had much success, though lately I've been having [quoted text clipped - 26 lines] > -Steve in Phx. > two_wheeled@hotmail.com > Could it be that you got the pressure and carb lines reversed? Raw fuel > shouldn't be able to get to the muffler through the pressure line unless the > outlet inside the tank is very low. Technically, raw fuel shouldn't be able to get directly to the muffler at all. If the engine is running, there's a positive pressure inside the muffler. That said, if the engine continues to act strangely, you should contact Hobbico. I have seen many strange things that "shouldn't" happen. I don't discount many explainations any more. If he said he saw raw fuel going up into the muffler line, I believe him. At certain times during running there actually is a negative pressure in the muffler. I can't imagine how it could result in a net negative pressure all the time, though. -- Paul McIntosh http://www.rc-bearings.com > > Could it be that you got the pressure and carb lines reversed? Raw fuel > > shouldn't be able to get to the muffler through the pressure line unless the [quoted text clipped - 6 lines] > That said, if the engine continues to act strangely, you should > contact Hobbico. I recall this was after I had filled the tank, so I am guessing since the tank was completely full, that after the engine was running and the tank was pressurized, a fluctuation in RPM may have allowed tank pressure to back up into the muffler. Just a guess. -Steve. > I have seen many strange things that "shouldn't" happen. I don't discount > many explainations any more. If he said he saw raw fuel going up into the [quoted text clipped - 23 lines] >>That said, if the engine continues to act strangely, you should >>contact Hobbico. > I recall this was after I had filled the tank, so I am guessing since > the tank was completely full, that after the engine was running and the > tank was pressurized, a fluctuation in RPM may have allowed tank > pressure to back up into the muffler. Just a guess. Then it isn't an issue. Just don't stuff every last possible drop in the tank. When it starts blowing out the vent, stop. Take a crank or two out. I ask again: How did you know that it was the "wrong needle?" Why did you replace it with a third-party part instead of utilizing Hobbico's top-notch warranty service? >>I recall this was after I had filled the tank, so I am guessing since >>the tank was completely full, that after the engine was running and the [quoted text clipped - 8 lines] > you replace it with a third-party part instead of utilizing Hobbico's > top-notch warranty service? Two details tipped us off the needle was wrong: 1) Closing the needle all the way would not shut off the fuel. The needle seemed to bind before reaching the stopping point. 2) At the field, another flyer had the same hobbico valve and housing, and was nice enough to let us swap them to check the fit. We compared the needles and his had a completely different taper and end point than mine. And when his needle was put into my housing, it fit perfectly. No, we never damaged the needle or the housing in use or with brute strength. I even replaced the housing, thinking that the seal inside it may have been bad. My needle fit and acted the same in the new housing. I called Hobbico and they are going to send a replacement. Until then I'll have to rely on the aftermarket valve. -Steve We compared >the needles and his had a completely different taper and end point than >mine. Just because two carbs on the same brand engine LOOK the same doesn't mean they take the same internal parts. I have two Webra Speed .32 engines, one about 5 years older than the other. Externally, the carbs are the same. However, the HS needle valves have a completely different taper. And when his needle was put into my housing, it fit perfectly. Some HS needles can't be closed off all the way. I even replaced the housing, thinking that the seal inside it >may have been bad. What seal? The only "seal" in the HS end of the carb is the needle valve and matching taper. You shouldn't have started tinkering with it, you should have called Hobbico FIRST. Dr.1 Driver "There's a Hun in the sun!" > You shouldn't have started tinkering with it, you should have called Hobbico > FIRST. Wait a minute, no tinkering?! That's why I got INTO R/C! :) -Steve. Sounds like you ay have gotten a returned engine and they replaced teh needle. -- Paul McIntosh http://www.rc-bearings.com > >>I recall this was after I had filled the tank, so I am guessing since > >>the tank was completely full, that after the engine was running and the [quoted text clipped - 24 lines] > I'll have to rely on the aftermarket valve. > -Steve > Hobbico shipped the plane with the wrong needle in the needle valve > housing. I replaced the housing, then realized it was the wrong needle > and out of frustration bought a Fox aftermarket needle instead-- > http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXG924&P=7 How do you know it was the "wrong needle?" The likelihood of such a thing happening is near zero. Anyway, if it was the incorrect part, Hobbico would have gladly replaced it free of charge. > Questions: > Can I remove the carburetor and low-end needle without damaging the > o-rings? If not I don't want to remove them without replacements handy. Unless you remove them with a hammer, you should have no problem. > What is a good starting point for the low-end mixture adjustment on the > carb? How about on the remote needle? Main needle is two turns out from fully closed. Low-end mixture is adjusted by setting the throttle to idle, closing the low-speed needle, (pencil-width opening showing in the carburetor), attaching a clean fuel tube to the fuel inlet on the carburetor, then blowing into the tube. Open the low-end mixture screw until you can distinctly hear air hissing from the carburetor. > What would cause fuel to flow from the pressure hose INTO the muffler > while the engine is running at low-to-mid throttle? This is only at > certain RPMs. I noticed it while running the engine in the garage. It > only happened twice. When it happened LOTS of fuel was being dumped out > the muffler through the pressure tube unburned. If the engine is running, there is a positive pressure in the muffler. Properly plumbed, the vent line is in open air inside the tank. The engine would have to be breaking several laws of physics for any appreciable amount of fuel to enter through the vent line... It's far more likely that the carburetor settings got way out of whack due to you fiddling with them without really understanding what you were doing. You won't have as much trouble as you gain experience. > Are plans / pics available to make myself an engine test stand? Bolt an engine mount to a post or something solid. Cut a U-shaped slot out of a scrap of 1/4" to 1/2" plywood to fit the engine. Screw or clamp the plywood to something solid. There are pictures of commercial stands on sites like Tower Hobbies. |
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