more engine trouble....
 

Ok guys here's the deal. A brand new Magnum .46 It ran fine trough break in, I ran it on Omega 10% nitro w/ 18% lubricant, heat cycling it like your supposed to, but keeping it pretty rich. Anyway, the low end wasn't quite right, because when you tried to throttle it up from idle it would die. An engine guy at our field told me it was a little to lean, and I richened it out. Then the engine ran great. When I tried to fly today, It ran horrible. It would idle fine, climb to peak fine, but when you went back to idle from the high revs it died. I thought, maybe the other day it was richened too much....so I leaned it a tiny bit out again, and it ran worse, and worse, and worse. Now, I reset the low speed to the manufacturers directions and it won't even run for longer than 5 seconds. I have both needle valves 2-1/2 turns out like how it tells you to set the default. When you prime it the engine fires right up but after a few sec's the burns out. Sometimes it will kick into reverse, but still die. Very puzzling. It just runs the prime off. It's almost like it lost back pressure, or something. I disassembled all of the the entire plumbing and checked for air/fuel leaks...found nothing. Any help would be appreciated. Thanks.

RE: more engine trouble....
 

Have you checked all of the fuel lines inside the tank? I had a very similar problem with a large gasoline engine, and the fuel pickup line inside the tank, (the one with the clunk), had fallen off of the brass tube. Your problem sounds like a fuel starvation.

Jesse

RE: more engine trouble....
 

Simple way to tune a nitro engine, asuming the fuel line and the tank is in good shape-start the engine and let it warm up with the glow igniter still attached, after a couple minutes remove the igniter and run the engine to full andpinch the fuel line before the needle if the engine speeds up lean it a little untill she does not speed up and then back it off a little then pinch again and she should speed up just a little you have the high speed set. Now the Low end-bring the engine about 2 to 3 clicks above idle and pinch the the fuel line again if she speeds up lean the low end untill she no longer speeds up and back it off the width of your screw driver blade and pinch again if she just slightly increases before dying you good to go.

RE: more engine trouble....
 

Sound like a bad glow plug. They do go bad, and break in can be particularly hard on glow plugs.

Replace the glow plug, then go back to basic tuning.

For future reference, if the engine was running well, the LAST thing you want to mess with is the low speed mixture, even if you're just resetting it to factory defaults. Each engine and running condition is different, and it takes too long to find that sweet spot again. This setting rarely changes once the engine is broken in.