engine trouble
 

Thunder Tiger PRO .36. I've run about 20 tanks through it so far.
I'm having trouble maintaining a low idle. It looks like there is just enough play so that the choke goes from slightly open to closed by itself.
Example: if I throttle all the way down there is a small opening. If I take a small screwdriver and wiggle the arm coming out of the carb, it has enough play to completely close the opening, killing the engine. (I didnt do this with the engine running).
We're thinking at idle, vibration may be causing it to open and close?
Instructor checked the throttle setup and said it didnt look bad. Servo rocks very slightly so I'll try tightening that.
I'll post a pic of the linkage at the carb. tonight, maybe you can see something wrong?


I also bought a tach last night.
I havent fooled around with tuning this engine at all. It flew fine from day one but now that I'm getting closer to landing I have to work on the low speed idle.
My instructor has been landing it, a little fast for him is ok but its time to get a good low idle on this. The book says 2000 rpm so I'll see tonight where I am now and then go from there...

Of course any suggestions welcome.

It looks like another rainy day. If there isnt enough sunlight for the tach to work, can you use an incandesnt bulb in front of the prop?
The tach says to use sunlight NOT a flouresent bulb shining through the spinning prop.


Steve

RE: engine trouble
 

running at night is not to safe because the 60hz of powered light effects the tach reading. So turning the lights off an using a flash light works butit's a little dawnting. The spring in the barrel should hold it tight I'd try to tune it first then look for air leaks. Search for the pinch test to set needles.

Rich

RE: engine trouble
 

It will still be daytime when I get to this after work but it wont be sunny.
I dont know how bright it has to be for the tach to work...?

What do you mean by "spring in the barrel"?
I dont think theres a spring there? I thought the throttle moved freely?? I'll have to look again.

I agree to try and tune first...

Thanks

Steve

RE: engine trouble
 

Steve,

I don't really know what you mean by choke!

The carb barrel should close all the way when the throttle trim is moved down. Sounds kind of like a linkage trim problem to me, although there maybe a problem at the carb that will not allow the barrel to fully close. Once you have the carb barrel opening and closing fully you should be able to set a good idle. This will allow you to taxi out and land at idle or just above, then trim down to shut the engine off once the flight is over.

RE: engine trouble
 

[quote]ORIGINAL: Steve Steinbring

Steve,

[I don't really know what you mean by choke! ]

I guess I mean carb barrel.

Steve

RE: engine trouble
 

I ran the engine tonight and my idle was at 3,500 rpm.
Trying to go lower stalled the engine.
The book says it should go down to 2,000.

WOT was 14,000 rpm

I need an electric starter to continue with this as I couldnt get it to restart.


steve

RE: engine trouble
 

My opinion, from the limited information available, is that the low speed needle is out of adjustment.

RE: engine trouble
 

I thinking the same thing?
I'm trying to get a low idle by closing the carb to much? right to the verge of dying..
How large should opening be when at lowest throttle setting.
could be I need to keep the carb open a little more and set the low speed needle???

Tonight I'll pick up an electric starter and do some more testing.

Now that I have the tach I feel more comfortable working on the engine as I dont yet know the difference between 2,000 rpm and 3,500 just by listening..

Thanks

Steve

RE: engine trouble
 

On a new engine it's tuff to set low idle but 20 tanks should be better than 3400 rpm be careful because the low and high interact any adjustments made to low must be followed by a high speed readjust. As you sneak up on idle try this when at lowest you can go pinch the fuel line if it does not change and then 1sec later speeds up it’s to rich go in ¼ turn. Pinch starts to die lean go out ½ turn but at throttle open 1/8 or more not much needle effect my TT25 idles at a crack can just see a small silt in barrel. BTW.. If you got a air leak you will never get a low idle.
The spring is on left side of barrel if you pull the barrel to the lever side you will notice it goes back to the needle side and rides on the screw than holds it all together.
Rich

RE: engine trouble
 

I chased a similar problem on a Norvel .061 setup I have.

First, you MUST get the low speed needle tuned. However, if there's too much play in the throttle linkage (a problem that plagues flexible steel throttle cables, especially if they must curve too much), on some, especially smaller engines, unstable idle can result. Get the mixtures right first, and if you still have troubles, think about this.

I fixed it by putting a light pen spring over the throttle cable, so that there was some tension on the cable all the time. Make it very light so as to not stress the servo, but strong enough to prevent throttle barrel floating, and it can help.

It's not a common fix to need, especially on engines over 0.10ci, and never should be needed on engines with straight throttle cable runs.

If you're using any threaded metal clevises in the throttle linkages, be sure to also use the jamb nut to prevent the threads from being sloppy.

J

RE: engine trouble
 

For a more controlled approach you may want to try a propellor with one inch greater diameter and one inch less pitch after you feel you have your tuning issues sorted out.

John