TT 46 Issues
 

Hi,

I've got a TT46Pro on my trainer, and it's fairly new (I ran about 20 tanks in it).

Starting the 10th tank I have this weird problem - The engines idles great , and we checked on the ground, it moves quite smoothly to full throttle. Immediately after take off the engine starts "coughing" very badly (I'm still in full throttle) and I have to reduce throttle (then 2 times I didn't, got a dead stick).

Around the time the problems started, I had when of my field's engine "expert" tuning my engine, and I remember him touching the idle screw (which I guess was bad idea). Now, when I remove the plug (OS #A3), the inside of the engine (I guess I sea the piston top) looks dark brown, so is the plug.

I'm using Omega 5% fuel. The prop is MA 11X6 or Thunder Tiger 10x6.

The fuel line seems to be fine, although after getting back from the field last time, I extended the tube in the tank so the weight will extend to the corner.

Any thoughts ? - Do I have a bad engine ?

TT 46 Issues
 

... Never use the spell check again :-) - it just changed every good grammer to bad.

TT 46 Issues
 

My engine had the same prob.it was all dark brown inside and guess what...my idling screw was also 'touched' by an expert and things got worse.Engine died after 5 mins every time it was started..Than i was told that the compression had gone and had to change the sleeve and piston.
Check your compression.If its alright than maybe the fuel is foaming in flight.
You also could be running lean.
overheating could also be a prob if its too lean.

Fuel draw
 

Amos,

How is your fuel tank installed?

Its centerline should be no more than 10mm above, or below the carburettor spray bar. The fuel tank must be wrapped in 6mm latex foam, from all directions, to isolate it from ANY AND ALL vibrations. No part of the airframe must touch any part of the tank, or the rigid fuel tubes.

Your fuel line to the engine should be as-short-as-possible. Fuel valves of any kind are the major cause of excessively long fuel lines.

If you adjust your engine to MAX-150 RPM, with the nose straight up, it should be rich enough to run under all circumstances. If your engine becomes lean under take-off run acceleration, it could be because your tank is too low, or your fuel line is too long.

The idle needle in the carburettor is there for a reason and should be adjusted properly.
If it is mis-adjusted by a person who apparently doesn't know what he is doing, you will have problems.

Go to Nisso Dekalo (or whoever sold you this engine) and exercise you engine's warranty, if your piston-sleeve have already gone south....

The piston top and the glow plug, are in a place where burning takes place and oil is burnt. You cannot expect to see things remain bare metal color...

TT 46 Issues
 

Try adjusting the needles yourself. It is not necisary to be an expert to get good performance from your engine.

For the main or high speed needle, ( the one that sticks out, and has a clicker spring on it) you start your engine run it to full throtle, and adjust the needle screw slowly to obtain peak RPM, then open the screw a few clicks untill you hear the engine slow down a littel. (maybe 300 PRM less than peak) to verify, you should be able to pinch the fuel tube and hear the engine increase RPM before it tries to shut down. If the RPM imediatly goes down the needle is set too lean, so open it a couple clicks and try again. another good test to do is run full rpm, then point the nose up, and the engine should remain near peak RPM. If the engine slows down it is too lean. Be sure to look at the fuel tube when you do this, if there are air bubbles going into the fuel line there is somthing wrong with the fuel tank.

For the idle screw, just insert a small screwdriver into the hole and open the needle about 1/8th turn. (engine not running) this will increase the fuel at idle and keep the engine cooler. The test for idle is about the same as the for the high speed, pinch the tube, there should be a short delay (up to 3 seconds) before idle speed begins to increase then it tries to shut down. if it does not increase RPM slightly it is too lean. the other test to do is simply open the throttle after several seconds of idleing and see how the engine behaves. if the RPM hesitates when you open throtle the idel is too rich, if it dies when you open throtle it is too lean. Be sure to allow up to 30 seconds of idle to allow the full effect of the idle mixture. (if idle is slightly too rich it takes a few seconds fo the extra fuel to build up inside the engine)

Sorry for the grammer and bad spelling.
best of luck and be patient, in a day or two you will be an expert yourself.

TT 46 Issues
 

Well, concerning the fuel tank it's just sitting there touching the ply ribs.... I'll roll it in foam before this weekend.

Does the length of the vent tube (the one that connects the muffler) matters too ?

The color of the piston doesn't concerns me as long it is normal.

I won't be able to deal with the warranty since this is a self-imported towerhobbies product......... :-|

How should I tune the idle screw - considering I don't know how is it positioned right now compared to the original factory settings ?

TT 46 Issues
 

....by the time I pressed "Submit" I got an answer for the idle screw question. Thanks!

Idle mixture adjustment
 

Amos,

First, adjust the high speed mixture correctly. The high speed needle must be about 3-4 clicks open, or 100-150 RPM down, from NOSE UP maximum RPM.

With the plane at runway stance, run the engine at maximum speed for a few seconds to clear it out, then close the throttle in a single motion, to about 1mm open, so the engine idles at about 2,500 RPM.

Now listen! If RPM gradually declines, the idle mixture is too rich.
Close the idle needle 1/8 of a turn, repeat the first paragraph and listen again.

If, on the other hand, idle RPM gradually increases, the mixture is too lean. Open the idle needle 1/8 of a turn and repeat the first paragraph.

Repeat the adjustment as appropriate, with ever smaller changes, until idle speed is steady. This is your base line.

Now check the response, or transition of the engine. After running at maximum speed, close the throttle to idle and allow it to stay at idle for about 30 seconds. Now open the throttle quickly.

If the engine rapidly accelerates to maximum speed, you are done.

If the engine stutters and spits fuel out of the carburettor (you could actually see this) before it eventually accelerates, or dies, it is too rich. close the idle needle 1/8 of a turn, run it at maximum speed for a few seconds and try again.

If the engine stumbles and hiccups before eventually accelerating (or dying), it is too lean. Open the idle needle 1/8 of a turn and try again.

Do either until transition is satisfactory, in ever smaller changes.

To check for mid-range richness, run the engine at 1/3 throttle (about half speed) for 30 seconds and open the throttle rapidly to full... This is for knowledge only, as most engine manufacturers, provide no adjustment facility for this.

Many engines, OS-FX for example, run too rich at part throttle.
You should exercise caution, so as not to cause your engine to shut down, when increasing from half to full speed.

TT 46 Issues
 

I just got back from the field.

The idle screw was set way to lean, and now everything seems to be fine.

But still - I found out that if the idle screw is not in the exact position it should be, the high speed needle doesn't affect the RPM.... lean or rich it sounded the same.

Thanks y'all for your help!

TT 46 Issues
 

Hi!
Don't be afraid to change the setting of the fuelneedles...they have no specific "best " position......You have to learn how to set them by listening to the way the engine sounds and set them accordingly...! This is very easy when you now how to do it.
Remember to always set the highspeed needle firts then the idle needle.
Before take off always piont the nose of the plane straight up
and adjust the highspeed needle a little rich so that engine rpm drops slighly (300-500rpm). This is easy to hear by just using your ear....a rewcounter is not at all necessary!

Regards!
Jan K
Sweden