Engine problems
04-30-2003, 02:51 AM
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Engine problems
Hi all,
I'm fairly new to R/C so beginners is where I'll post this question. I have a Midwest Citabria with a TT 90 4 stroke that I bought used here on RCU. I got it out to the field tonight for the first time. The engine starts easily and idles nice and smooth. But at high rpm's the needle valve is extremely sensitive, and when raising the nose of the plane the engine immediately slows and dies. I pulled the tank out to make sure there was a clunk at the end of the feed line, which there is. It was suggested that I clean out the carb and needle valve, and possibly replace the o-ring. Any other suggestions?
Thanks!
I'm fairly new to R/C so beginners is where I'll post this question. I have a Midwest Citabria with a TT 90 4 stroke that I bought used here on RCU. I got it out to the field tonight for the first time. The engine starts easily and idles nice and smooth. But at high rpm's the needle valve is extremely sensitive, and when raising the nose of the plane the engine immediately slows and dies. I pulled the tank out to make sure there was a clunk at the end of the feed line, which there is. It was suggested that I clean out the carb and needle valve, and possibly replace the o-ring. Any other suggestions?
Thanks!
05-01-2003, 12:19 AM
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Engine problems
A little to agressive on the needle? Perhaps, but I have a hunch there is something else agravating the obvious leaning.
Many Cubs and Cub like airplanes and that includes the Citabria are very difficult to locate the fual tank high enough to center it on the spray bar. Many are reluctant to cut away the instrument panel to accomplish this when they are using to large a tank to begin with. The result is frequently with the tank to far below the spraybar and engine problems. I trust you are using a sideway mounted engine. If its upright then the above problem becomes extreme.
John
Many Cubs and Cub like airplanes and that includes the Citabria are very difficult to locate the fual tank high enough to center it on the spray bar. Many are reluctant to cut away the instrument panel to accomplish this when they are using to large a tank to begin with. The result is frequently with the tank to far below the spraybar and engine problems. I trust you are using a sideway mounted engine. If its upright then the above problem becomes extreme.
John
05-01-2003, 02:39 AM
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Engine problems
old propnut,
I wasn't aware there was a choke assembly on a 4 stroke glow engine.
John Buckner,
Yes, the engine is mounted horizontally. The tank is mounted up high, and the fuel lines are run out the top of the firewall, not inside the mount.
Thanks guys, keep the ideas coming!
I wasn't aware there was a choke assembly on a 4 stroke glow engine.
John Buckner,
Yes, the engine is mounted horizontally. The tank is mounted up high, and the fuel lines are run out the top of the firewall, not inside the mount.
Thanks guys, keep the ideas coming!
05-01-2003, 12:02 PM
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Engine problems
No, there's just a third line with a filter in it. I am going to replace the tank because there's some crud in it. This is why it was suggested I clean out the carb. I will be moving the filter to the carb feed line.
05-01-2003, 03:18 PM
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Yes. Normally I like to have a 3rd line with a clunk in the tank. It just occurred to me that the line had a screw in it as a plug. I switched to the little DuBro plastic plug, but it fits loosely. Are you thinking it might be causing a problem?
05-01-2003, 05:24 PM
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Engine problems
If you can't get the engine to richen up by opening the needle way way open, then one more thing to check is to make sure you don't have any kinks in the fuel lines and that you don't have too small fuel line installed.
If you can get the engine blubbering rich, and it still leans way out when pointed nose up, then you may have a pin hole in the lines. It's possible to get a pinhole that only opens when the tubing is flexed a certain way or under vibtraion.
You may also have a fuel foaming problem. When the engine is running, can you see the fuel line? Do you see air bubbles?
If you can get the engine blubbering rich, and it still leans way out when pointed nose up, then you may have a pin hole in the lines. It's possible to get a pinhole that only opens when the tubing is flexed a certain way or under vibtraion.
You may also have a fuel foaming problem. When the engine is running, can you see the fuel line? Do you see air bubbles?
05-01-2003, 05:38 PM
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Engine problems
Here's what I did:
a)Opened needle 2.5 turns, started engine.
b)Idled real nice & smooth
c)Throttled up to full, ran ok at first, ended up adjusting needle to 2.0 turns. Any adjustment from here <1.8 or >2.2 turns and it immediately started to stumble, but ran ok at 2.
d)Watched a crash and another flight.
e)Got some help.
f)Started engine back up (still at 2.0).
g)Real nice idle - low end is great.
h)Ran back up to full throttle, engine's rough.
i)Adjust to about 1.1 turns out. Anything less, or anything more than 1.25 and it stumbles. Raise the nose and it immediately dies.
No air bubbles in fuel line. One real puzzling thing is that the needle valve is SUPER sensitive. One or two clicks and the rpm's are bouncing all over. That's what lead one person to suggest maybe a bad o-ring on the valve.
a)Opened needle 2.5 turns, started engine.
b)Idled real nice & smooth
c)Throttled up to full, ran ok at first, ended up adjusting needle to 2.0 turns. Any adjustment from here <1.8 or >2.2 turns and it immediately started to stumble, but ran ok at 2.
d)Watched a crash and another flight.
e)Got some help.
f)Started engine back up (still at 2.0).
g)Real nice idle - low end is great.
h)Ran back up to full throttle, engine's rough.
i)Adjust to about 1.1 turns out. Anything less, or anything more than 1.25 and it stumbles. Raise the nose and it immediately dies.
No air bubbles in fuel line. One real puzzling thing is that the needle valve is SUPER sensitive. One or two clicks and the rpm's are bouncing all over. That's what lead one person to suggest maybe a bad o-ring on the valve.
05-01-2003, 05:41 PM
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Ok, try this. Get it set, then just push and pull sideways (not in-out) on the needle, don't turn it. If you get rpm changes, it's the o-ring for certain.
The Mag carbs are really prone to this. Put a bit of fuel tubing over the needle to serve as a gasket, I do it to all my Mags and it fixes all kinds of mixture headaches.
The Mag carbs are really prone to this. Put a bit of fuel tubing over the needle to serve as a gasket, I do it to all my Mags and it fixes all kinds of mixture headaches.
