HI all, i am new to the hobby and i have a .61 ThunderTiger PRO engine, i've had a lot of issues with it. Initially broke in with fuel without nitro. After 10 flights it stabilized and i thought was broke in. I have now 5% nitro fuel. It is overheating, even when running rich as it pops a lot when i apply full throtle with a rich setting on the needle, is running on 11K rpms and a 11x7.5 prop which is the recommended one. Have an OS8 glow plug that glows fine when i check it out of the engine. The engine runs unstable in either lean or rich setting and then shuts off unexpectedly. Very overheated, i notice a strong vibration when running it over 8K RPMs, don't know what to do it seems is not the needle. Altitude in here is 7500ft, no fuel leaks on the system. Any clues to check ?, how do i know if that vibration is normal or causing the overheating ?, i can't even touch the muffler because temp. Not lean as a lot of smoke and unburnt fuel comes out of the muffler. It hesitates to pick speed when throtling fast, i do not know what to do, what should i try ?.

Thank you,
Felipe

A hot muffler is normal.
If it pops and sputters when you advance the throttle, it sounds rich.
Strap the plane down and carefully adjust the main needle at full throttle until the RPMs peak being careful not to lean it (clockwise) once peak is reached. In other words, once the revs start to fall off as you turn the needle in, quickly turn it back out so you don't overheat it. Now, once the peak is found, adjust the needle out (rich/counter-clockwise) three clicks. This should be a good starting point for the top end and keep it from sputtering.

Kirk

Tried that already i can adjust the needle using that criteria, it still hesitates on picking up speed when accelerated, it stops suddenly overheated even when running rich, what else can i try ?

Hi,
I would look for bubbles in the fuel line when the plane is in the air. It can seem rich but still be going lean when this happens. A defective or unbalanced prop can cause this (and the vibration). Be sure your fuel has enough oil. A little castor might help. Otherwise there might be something wrong with the engine. A peeling cylinder liner is the first thing that comes to mind. Good luck.

If it sputters and hesitates when the throttle is advanced from idle, but runs smooth when full, the idle is rich.
Lean out the low needle in small increments until it idles for a long time without this 'loading-up'.
How do you know it's overly hot? Did you measure the temp some way?
Old fuel will cause a flame out as well as an old worn-out plug.
If the prop isn't balanced and the tank not cushioned, the fuel can foam from the vibs causing a leanout at full throttle.
Does the compression feel strong?

Kirk

Go with Texasbird's suggestion..

I will add the following.

An engine will not overheat with a rich mixture.
There are exceptions to this:

1) bearings are really shot. You will hear this, and can feel this turning the prop over. If it is bad enough to get the engine hot, it will be obvious.

2) the engine is in cowled-in installation, and there are not adequate or properly placed air inlet and air exit openings

Since you noted that you were new to this, I will assume for a moment that this is not a cowled-in or scale application... and the engine cylinder is out in the breeze.

Ruling out the two above....

If the engine is overheating no matter of the mixture setting, you ARE getting air in the fuel system

Air comes from two sources. Fuel foam, and leaks. You have one, or both happening.

This will cause you all sorts of headaches with transition and everything you described.

Assuming the engine has not been crashed and the crank shaft is not bent....

1) BALANCE THE PROP !! If it is shaking, something is out of balance. Modern engines run smoothly at nearly all power settings. Change the prop, and make sure the new one is balanced.

Shaking WILL cause the fuel to seriously foam in the tank, introducing air into the fuel which will cause the engine to run lean, no matter what, and it will over heat rapidly.

If the engine runs OK at low speed, sorta ok in mid range, and will not run at full throttle in the air... it is highly likely the installation is generating foam in the fuel.

Balance the prop. Make sure the tank is isolated from the fuselage structure - wrap it with foam. (see item 3 while you are at it)

2) Check the fuel lines running from the tank to the engine. If you have a remote needle (see 2a) replace the tube from the needle to the carb. Make sure the vent line and feed line are flowing freely and are not kinked. Make sure the pressure/vent line is properly connected to the muffler pressure fitting, and that fitting is not clogged. You should be able to GENTLY blow into the vent line, and cause fuel to easily flow out of the feed line.

2a) Note if you see clear fuel going to the needle, but bubbles in the remote needle to carb fuel line, there is a possiblility the needle valve o-rings are not properly sealing, allowing air into the system.

3) Remove the fuel tank. Check the clunk & pick-up line inside. Clunks and tubes often fall off, or the tube ends up with a cut where it mates with the metal tube. This is very common and can drive you nuts! Make sure the clunk is not stuck against the back of the tank. It should move freely at all times.

4) Pull the engine from the airplane. Check ALL of the bolts on the engine. Yes, on a 2 stroke engine, the crank case is part of the fuel system. The bolts and covers are potential sources for air leaks. Make sure the crankcase/backplate bolts are tight... the head bolts... everything. Don't go nuts an strip them, just make sure they are snug. A leaking backplate or loose cylinder head can cause some of the problems you noted.

5) Make sure the carb is properly installed. This is a potential source of an air leak. On the TT61 I believe there is an O-ring seal at the carb/crankcase interface. Make sure the carb is pushed down against the seal, and the retainer is snug.

6) Change the glow plug. Might be ok, but it ever hurts to try. Make sure the glow plug is tight (Again, don't go nuts here) The OS8 is a great plug for the engine. K&B plugs, Merlin plugs, Tower plugs... all suitable for that engine. There are few that are not good. However, on rare occations glow plugs develop leaks in the center seal, or could leak around the crush gasket. Does not hurt to check if nothing else above worked.

Often times people have written to me with symptoms where the engine runs well on the ground, but the needle goes away in the air... and the engine gets lean and hot. That is a classic symptom of foam in the fuel. You may not even see bubbles in the fuel supply line on the ground, but when the engine unloads a bit in the air, it hits the right note to foam the fuel.

I hope this is helpful

Bob Brassell

Jett Engineering
Engine Mfg Support Forum

Hi,

You mentioned that you are new to the hobby. Just wondering if you are adjusting the low speed needle setting as well as the high speed? The hesitation and rough running (uneven firing?) sounds like the carb. is not transistioning (low speed to high speed needle) well.

tks all for your valuable help
I will doublecheck the tank installation and cushion to avoid foaming, the prop is balanced already, i have 2 questions, the altitude in here is 7500ft how does that affects ?, and i have an exhaust deflector can that cause the temperature or popping ?, also if the fuel is foaming even with a richer needle set should the engine be still ejecting unburnt fuel ?. I have setup up the idle screw a lot of times and still see a troubled transition from low rpm to highs. Another observation was that when the tank is at 1/4 level the situation improves in terms of smoothness but engine still overheated according to other people on the flying field. How can i know to recognize that the engine is overheated or not ?

IMO different engines like the tank located at differnt levels. On an engine I'm having difficulties with now I have the top of the fuel tank level with the center line on the carb. It runs fine when on the ground. But if I lift the tail so that it's level, the transistion goes rich and the engine stumbles.

Can't speak directly to the elevation but one would think the carb would tune for it. I wouldn't worry about that.

Different engines run at different temps. I have a temp gun that I use but can't get very much information from that. Once I had an engine that no matter what I did it ran very hot. It would melt the silicone coupler off the tuned exhaust system. The pipe would turn white hot! My wife picked it up and it took the skin off her arm from elbow to wrist. On a really hot engine, they will flame out or seize. Other signs is burned oil (black) coming out of the exhaust and excessive staining from burn oil on the outside of the engine.

You might decide to run your engine on a bench to eliminate variables associated with the plane. Then you'll have a better idea what your up against.

Very good point. I'm sorry I did not mention that up front.

When ever you suspect an engine problem, put the engine on a test bench. If the problem is with the engine, rather than the installation, it will be evident pretty quickly.

Running at 7500 feet will cause a drop in output power, but should not cause overheating.

If the engine is indeed running rich, and there is definately visible un-burnt fuel coming out of the exhaust, and it is still getting hot.... there is an internal problem with the engine, such as the bearings, bent crank, bent rod, distorted piston, or peeling liner as had been mentioned earlier.

The 'popping' noise you discribed is unusual. Have you disassembled the engine in the past ?

My experience over 28 years has been that 85% of suspected 'engine problems' are traced back to the fuel system or engine installation.

My personal experience is that 85% of engine problems are related to operator head space and timing which includes improper installation and setup of engine and fuel system.