For 2 consecutive weekends I have had problems with my Supertigre GS-45 (turning a 10x7 prop) which is installed onto an Avistar trainer. The engine runs well when tested in the floor even when making quick changes in the throttle up and down. However in the last flights I have made I have detected some coughing (or should I say sputtering) that happens when I do small adjustments to the throttle (2-3 clicks up or down) just to fight the wind and after that it continues to run consistently. I must clarify that this coughing doesn't happen all the times I do these small adjustments in the throtle.

Yestarday this coughing happened just when I was making my first turn after the takeoff and it kept sputtering while I was fighting to avoid the plane fm stalling... at the end gravity won and I had to run to the place I saw the plane crashed expecting to see bits and pieces all over... Lucky me it fall into high grass and that absorbed the impact with just a cracked elevator stab...

So, while I am in my way to repair the avistar I keep thinking what is wrong with the engine... I checked the fuel tank and the fuel lines and everything seems to be ok... I am using powermaster fuel but I am not using fuel filter... could it be the engine is clogged with some stuff fm the fuel? Should I clean it? How to?

Sounds like the low end is rich. Try leaning the low end some. That is the needle in the center of the throttle arm. After you make any adjustments run the engine up to full throttle to clear it out. Then idle back down and see how you did. BTW the high speed needle is only effective for the last 1/3 or so of throttle. Everything else is controlled by the low speed needle. Just be careful making the adjustments. I would shut the engine down when making the low speed adjustments. Then restarting the engine. Be careful and good luck.

Mark Shuman

Has the engine been in a crash?

The reason that I ask is because mine was... I thought I had cleaned it well (it took a lot of dirt into the front end) but apparently I wasn't as thorough as I thought I was.

Just by pure chance, I had gotten my hands on a microscope and for the heck of it, looked at the needle valve - it was scratched and gored pretty badly. That was the reason that my particular engine ran poorly.

I'm just wondering if you are in a similar situation?

Bob

N1EDM,

This engine has been only on the crash I just described on the first post. And it was not even dirty by the way the airplane fell...

I've been thinking about cleaning it anyway but do not know even what fluid to use for the claening.

phread59,

It makes a lot of sense to me that the low end may be rich as it shows no bad tendencies when running at full throttle. How much of a turn is the average adjustment to this needle? 1/4 turn, half turn?

If it was a gentle crash, then what I described in my previous post probably didn't happen, unless you somehow took dirt down the carb. It didn't sound like you did.

In my own case, I had dug a bit of a trench and the engine was buried.

When I crashed, I pulled off the engine and kept it immobile, then disassembled it back home. I was able to scoop out most of the dirt from the carb intake, pull off the carb, then flush more dirt out of the crankshaft. Then, I was able to disassemble it further. I found more dirt once I opened the rear cover.

My guess is that i didn't do as thorough a cleaning of the carb as I thought I had, and some dirt got in the NVA to create those gouges. That probably didn't happen to yours. I replaced the Needle Valve (LXFY19) and the Spray Bar Assembly (SUPG5945). The numbers I referenced are from the TH web site, if they are any help to you.

I just used glow fuel to help clean, though any solvent like that will do - a bottle of alcohol will do (denatured, or the rubbing kind, not the drinking kind). I used some after-run oil to lube up the bearings and other sliding parts as I rebuilt the engine.

I had another thought. Check the nipple where the fuel enters the carb. I had one loosen up once and it caused problems.

Tighten it CAREFULLY... it won't take too much effort to strip those threads. Remember the old saying "Brass to brass, don't break your, um, butt". Most will have some kind of a fiber washer to make a fluid-tight seal.

Just another $.02

Bob

How much time do you have on the engine?? ST's can take awhile to break in and very small adjustments on the low end needle will be needed for awhile. Just keep playing with it and soon it will run right and once you reach that point it run great!!!!! I love these engines but they can be a bear to get right and broken in.

Check your back plate for loose or missing screws, seen it twice last month.

Is the tank wrapped in foam rubber? If not do so. Helps prevent fuel foaming and inconsistent engine performance.

I have been running this engine 1 or 2 filghts every weekend for about 4 months... at the time I did the break in with the help of one of my field instructors it was very hard to do as the engine was really tight but fm then it has been running ok until 3 weeks ago when I started to hear the small sputtering at about half throttle...

I said adjusting the low end needle makes sense to me as previous to the problem I remember another of the field instructors did an adjustment to this needle on my engine but did not followed up for the real effects after that...

I already know a bit about how to adjust the high end needle and how the sound should be when leaning or richening the engine.... However, as far as the Low end needle adjustments I am totally ignorant of how much of a turn is a proper adjustment or how the engine should sound if running too lean or too rich... Any guidance will be highly apreciatted.

Please see the instructions on how to set your SuperTigre engine's carburetor. They can be found in the Engines forum in the SuperTigre forum. The instructions are in a 'sticky' at the top of the forum.

I agree about S-T's requiring quite a bit of breaking in. Had lots of trouble with my gs 40 right off the bat. You might want to try a different/new glow plug, I noticed mine making a different noise at full throttle, then it quite at idle on the deck. New glow plug fixed everything. Don't know what kind of Glow Plug you're running, but (my opinion here) if you're not running an OS you're asking for trouble. OK, Enya plugs are good too. Don't buy a cheap glow plug.

A 10 x7 plug on a .45? I'm pulling an 11x6 on my 40.

Andy

a65l,

I am using OS A3 glow plugs... after the crash I checked the glow plug and it still shines in a very intense manner when tested with the starter...

Do you think 11x6 prop is better for the GS-45?

Yes 11-6 is a good choice. When adjusting the low end needle. No more than 1/8 of a turn at a time. With the low end a little goes a long way. The a-3 should be fine. Mine has a Fox long with idle bar in it. works fine for me. I would however try one without an idle bar. I just happen to have a bunch of the Fox's. Good luck getting it to run well. BTW I am using an APC 11-6 on mine with good results.

Mark Shuman