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Engine trouble - what to look for?

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Engine trouble - what to look for?

Old 03-15-2007, 05:33 PM
  #1  
weeber24
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Default Engine trouble - what to look for?

I crashed my Pulse XT this past weekend, thankfully the damage isn't bad, but I crashed due to engine trouble that I really don't understand, and I want to know everything I should check before going back up again. FYI, the engine I have on it is an Evolution 46 with all the stops removed from the high & low speed needles, running 15% CoolPower. I'm going to give all the details I know, so bear with me.

When I first got to the field, I bench tested the plane and engine. The engine did not want to throttle up. It would idle great, but as soon as I gave it full power, it would increase in RPM for a second and then die down to an idle. Richening up the high-speed needle valve seemed to solve the problem and the engine did fine on the bench after that. I made sure to run it with the high-speed needle a few clicks on the rich side. The first flight went great, inverted passes, loops, rolls, reverse split-S's (flying inverted then giving it full "down" elevator to do a negative G reversal), and then I brought it in for a nice landing.

Things got interesting on the second flight. Takeoff was fine at full-power, but something went wrong with the engine after a couple of minutes. Unfortunately, I didn't realize something went wrong at that instant because someone was ground test their engine, and I couldn't hear my plane. I brought it close for a pass with the engine at idle. Finally saw and heard that the engine was running fine, but as I tried to throttle up to go back around the same thing happened as on the bench. Transition from idle to full power, the engine would jump up in RPM for a second and then drop back down to an idle (but it didn't die). Unfortunately I found my self low and slow and at the wrong end of the runway, I ended up putting the plane in some trees/brush.

Things aren't too bad, it's all repairable, but I'm trying to figure out what happened, especially since my first flight of the day went great. My first thought is maybe my high-speed needle "walked" itself lean, but the needle is still tight and does a good, solid "click" when turned. Plus nobody at the field had really ever heard of this happening before. It may have been a fuel flow problem, but the tank seems good and holds pressure when I blow into one line and plug the other. I think I'm going to put the stop back into the high-speed needle to make sure it doesn't go lean if it is walking itself. But I would like to hear from you guys if there's anything else I should be on the look out for? Any other theories on what might have happened?
Old 03-15-2007, 07:40 PM
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Default RE: Engine trouble - what to look for?

I'd check to make sure the pick-up line in the tank didn't get kinked after pulling out of inverted flight, leaks in any fuel lines, or foaming of the fuel in the tank, or crud in the carb. It sounds as though you have a lean-out condition as you suspect.

bhady
Old 03-16-2007, 12:53 AM
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Tired Old Man
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Default RE: Engine trouble - what to look for?

Check the condition of the fuel lines at both sides of the needle valve. Especially the one between the needle valve and the engine. I've seen a few of them now with leaks at those locations that drove the owners nuts.
Old 03-16-2007, 08:19 AM
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Default RE: Engine trouble - what to look for?

Replace the glow plug. This sounds like classic bad glow plug behavior. Whenever an engine that was running great starts requiring adjustments it didn't need before, or starts exhibiting poor behavior, its probably the glow plug. Its the easiest thing to check as well.

Brad
Old 03-16-2007, 12:01 PM
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Default RE: Engine trouble - what to look for?

just because a glow plug glows does not mean it is good.sometimes the filament can get knocked out of alignment from the combustion process or even coated with a clear deposit that was from the synthectic oils and prevents the catalytic action between the platinum element and the methanol.any time an engine starts to sag[lose rpm] when you increase throtle it is going lean[too much air/not enough fuel]as stated above check for leaks in your fuel tubing or even foaming in your fuel tank.
Old 03-18-2007, 09:44 PM
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Druff1
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Default RE: Engine trouble - what to look for?

I'm having the exact same problem with mine. It seems to run a little better now that the outside tempature has warmed up, but still leans out when flying for about 4 minutes. When i go to full throttle, the motor will start to rev up and down a couple of times and then die. It doesn't seem to do it on the ground when i'm tuning it. I know it has to be leining out, but i can't figure it out.

Also, i've removed the baffle out of the muffler and i think that helped a little, but still having the same problem
Old 03-19-2007, 06:13 AM
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Flying freak
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Default RE: Engine trouble - what to look for?

try running a full tank on the ground the tuning might be changing at the temps go up looks for fuel issuses and such...
Old 03-19-2007, 01:31 PM
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Default RE: Engine trouble - what to look for?

I keep a chart in my flight box to help diagnose such problems. I’ve pasted the section that lists all the possibilities that could be causing the problem you’re having.

Good luck

Engine not broken in
Bad plug gasket
Fuel line too small
Leaking qlowplug stem
Glowplug shorted
Blocked fuel vent
Glowplug blown
Pickup in tank off
Bad fuel
Crack in crankcase
Debris in fuel line
Varnish in engine
Air leak in tank
Bearings worn out
Air leak in line
Bearings defective
Kinked fuel line
Bearing misaligned
Carb leaking air
Crank rubbing back plate
Debris in filter
Split tubing inside tank
Clogged needle valve
Propeller too large
Loose engine
Improper carb setting
Foaming of fuel
Improper tank location
Loose head
Propeller out of balance
Loose case screws
Propeller too small
Loose plug
Old 04-05-2007, 02:10 PM
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foamer
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Default RE: Engine trouble - what to look for?

Same eng same problem Twist PNP with Evo 46 checked all of the above if you find it please post. new fuse on the way think I'll use the saito 72 this time.
Old 04-05-2007, 08:48 PM
  #10  
Druff1
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Default RE: Engine trouble - what to look for?

I was working on my Pulse XT last night and took the Evo .46 motor out. Then i noticed that when i put the fuel tank in i put it on top of the extra plywood plate in the bottom of the plane, which is for the batteries when running electric motor. This made the fuel tank way below the engine. I won't get a chance to run it till this weekend so i don't know if that will help the leaning issue.
Old 04-06-2007, 09:49 AM
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tucker1865
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Default RE: Engine trouble - what to look for?

Had the exact same symptoms...after the engine experts messed with it for awhile, we finally noticed that a carb retaining screw was missing and the engine was sucking air.

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