Ever since I started flying I've been having problems with this engine. On my first flight I lost the back half of my muffler, but that was only a sign of things to come. Everytime I started flying, the engine would come to life, have full power, and it would fly great. After about 5 minutes, the engine noticeably starts to lose power, and maybe after 10 minutes I have to bring it down before the engine dies (which has happened a few times) Everyone at the field would just tell me it's because it's a new engine, but after going through more than 10 tanks, and not noticing any improvment from the first flight, I'm starting to doubt that claim. It finally caused me to crash last Thursday by dieing right after taking off on a second flight when it was still hot from the first.

After I fixed the plane back up, I've had nothing but trouble with the engine. When giving it full throttle from idle, it will get a lot of power, then slow down, then speed up a little more than it slowed down, it does this several times gradually moving up to "full" power. I say "full", because at full power it only gets enough power to actually drive around on the grass field. It doesn't have a chance to get off the ground. Even if it did, I would probably still have the problems with it losing power after a few minutes and having to bring it back down.

I noticed that a large pool of fuel is building up on the bottom of the muffer. I'm kind of figuring that it's fuel from the exhause coming around but it seems kind of excessive and didn't exist pre-crash. I'm kind of thinking there is damage and it's leaking somehow, but then again, it could be nothing. Could someone explain what might be the cause of this?

The engine I have is a .46 Magnum GPA (I dont even think they make this anymore. I got it 4 years ago but only started using it a few weeks ago). I'm using 15% nitro, synthetic/castor 80/20 wildcat fuel.

I really can't tell a change in performance from making it half a turn richer or leaner. I don't really want to move it a lot from the place where the people who know what they're doing set it. I don't know what the engine manufacturer recommends; god only knows where the manual is.

Does anyone have any clue what could be wrong with my engine? I'm about to go buy a new one tomorrow, but I don't want to blow a lot of money away because of my incompetence.

It sounds like you may have run the engine lean a few too many times, and now it's toast, but it could be a number of things, like air leaking around the needle valve or around the front bearing, or it could be a pin hole in a fuel line...

It would be best to have someone experienced look at it. You can not however, expect that once someone with experience tunes the engine, that it will be set right forever. These things have to be re-tuned periodically, especially when you have temperature or large humidity changes.
Dennis-

Could someone tell me what this screw by the air intake does?

I have a feeling this might be the cause of my problems. After I was done taking the engine off of the mount, I noticed this was pretty loose. It probably would have vibrated out after a few more flights.

It has a spring around it, and it doesn't seem to hold anything together or in place, so I'm guessing it has to do with how the engine runs. Unless they just wanted to put an extra screw in there for fun. Is it supposed to be screwed in all of the way? Could this be part of my problem? I won't be able to test it until tomorrow.

If this is something unique to the engine I can get a few more pictures so maybe people who have a better understanding can get an idea.

edit: I have nothing to do, here's a few more pictures anyway:

How many new and what make glow plugs have you tried ?
The black screw should be the throttle body stop and no clue on the phillips one.
What adjustments have you made to the low end idle screw ? It sounds too rich to me.

When I was having problems with the engine jumping up and down in power I took out a gloplug I had only used in 3 flights and put in a new one and there was no difference. The type of glow plugs I've used are Thunderbolt long plugs.

That philips screw is the same screw I have pointed out in the other pictures. I see what it does now.

Have you adjusted the low end idle screw ?

No. It hasn't been touched.

Try turning it in 1/8 to 1/4 turn to lean the mixture then open main needle slightly. Of course, if it's then worse, go the other direction.

Sounds to me like your engine is way off. The low and high end adjustments, although separate work together and everytime you adjust one of them, you should readjust the other until you bring it all together. Check you idle by piching off or removing the fuel line from the carb.

If the rpms increases before the engine quits your low end is to rich. If the rpm just goes down and dies-too lean and adjust as necessary.

Also chek you fuel lines for crimping. If they come out of the firewall and make a sharp 90degree turn to the carb,could be crimped enough to cause a lean run , overheating and landing with your throttle stick full open yet barely running and hottttt.

The screw is the idle stop screw. It adjusts how far your carb can close down. If you screw it way in, the carb will not close.

If you are flying a trainer and are new to RC, you are probably running too lean. Our engines are simple things without fuel pumps. Fuel is sucked into the carb by venturi action and the fuel level in the tank can change the needle valve setting. Your engine needs to be set slightly rich at the first of a tank or it will go lean towards the end of the tank, espacially if the tank is low relative to the carb. Trainers are nortorious for having low tanks, causing the engine to run lean at the end of the flight.

Fill your tank about 1/3 full, no more. Crank up and lean out to max power, then open up a couple or 3 clicks. Stop the engine and fill the tank. You'll probably notice the engine is running slightly rich. This is the setting you need to start with to have the engine run well for the full flight.

I mounted the engine to a 2x4 and held that down to my flight box with rubber bands and completely retuned the engine from all the advice from this thread and some others. I was running way to rich on the highspeed needle and leaned out the low end a tiny bit. It's now running faster than it ever has before. Thanks for all of the advice. Hopefully the weather holds up tomorrow [8D]

One thing I noticed though is that it's getting extreeeeeeemely hot, and very fast. I probably only had it running on full throttle for 30 seconds but I would easily have burned myself if I touched any part of the engine. Is this anything to worry about? I don't know how hot these engines are supposed to be running.