Hi guys! I'm a beginner R/C'er who has flown four times now. I've got a brand X trainer with a OS 40 engine. The guy that gave me the engine helped me initially start the thing and get it leaned out correctly. My first flight went great as far as the engine is concerned. It started and ran fine. My second flight was the same. Now, my last two flights I have been having problems getting the fuel/air mixture set right. Seems like I can't find that sweet spot. I was taught to find the mixture which allows the engine to run at idle and full throttle in all attitudes. Seems like it should work right? Anyhow, I've been able to apparently get the engine running right, but during my flights, it is obvious that the mixture is still not right. I love flying the plane so much that I usually keep flying despite not having full power. On one of my flights I had landed to mess with the fuel and I just got frustrated with it cause I was wasting time with it on the ground and not enjoying flight time. I ended up taking off and flying it anyhow! I am a self taught beginner in RC so I am learning as I go. I have my private pilot's license to fly the big birds, which has helped me alot in learning RC. It doesn't help me however with these small glow engines. I have tried new fuel by the way and seem to get the same results. Maybe a new Glow plug? Any help you guys can give me would be greatly appreciated! I guess I need a beginners guide to setting up your glow engine!

Get an OS 8 glow plug to eliminate one possible source of problems. Also make sure that the fuel lines are O.K. with no air leaks. Even microscopic leaks will cause tuning problems. There should be no air bubbles visible in the fuel line.

In general, once the engine has been properly tuned there is little need to fiddle with the carburettor.
At most one has to adjust the main needle a couple of clicks either way to compensate for temperature/humidity changes, but no more than that.
As you may have noticed engines tend to lean out once in the air. My advice is to tune your engine slightly on the rich side on the ground.
If you don't have it, download an engine manual from [link=http://www.osengines.com/manuals/index.html]http://www.osengines.com/manuals/index.html[/link]. It will tell you how to properly tune your engine.

/Red B.

I set all my engines to run perfect. They do and when one of them starts acting stupid and its hard to keep a setting or a good idle. I change or check the plug first to see if that takes care of it. Most of the time it does. There are many things that can cause an engine to run poorly. If your engine is not "properly tuned", you can be chasing shadows. I fond that many people do not have peoperly tuned engines. They think they do but are way off. Whenever I ask if they checked what they adjusted, they don't know whatI am talking about.

They we have guys with problems and they add or change things which only maks the orignal problem. It may seem like youcured it but you didn't, you only changed things a bit.

Once you have the low end set (idle ) you should not need to touch that again.

For the high speed needle I do the following:

1. "Peak" the engine, then back off about 1/8 th turn on the needle valve.

2. Next, I move the transmitter throttle to wide open, and pick up the plane and point it nose up. Hold it in a nose up position for about 20 - 30 seconds. The engine rpms should stay the same. If it speeds up and dies, you will need to open the high speed needle some more. If it "stumbles", you will need to close the high speed needle a LITTLE.

3. Repeat until the engine runs the same with the nose pointed up for 20 - 30 seconds.

After that, you shouldn't have to move the needle valve more than one or two clicks to compensate for humidity and/or temperature.

Thanks guys for the great info! I'll give your suggestions a try. I still am not sure of all the lingo yet. For instance , setting your high speed needle...is that in fact running full throttle? Does anybody use a tach when setting your mixture? When I lean out a Cessna 172, I run it up to 1700 RPM and lean out until I get an increase in RPM, followed by a drop. Then I enrichen back just short of the peak RPM. Seems like your method is similar, Campy? I think I will download the OS manual and also try to find articles in the magazines concerning proper tuning. Plus I'll pick up a couple of OS 8 glow plugs. Thanks again guys for helping this newbie out! Just another quick question...what does the different percentages of nitro do for you and do I need to be concerned with overheating with too high of a nitro concentrate? I've been running 15% but my new jug is 25%. Any problems with this for a .40 engine? Thanks!

Hi,

Most engines don't need more than 10% to 15% nitro. I have been running 10% for many years in my motors which include an OS 40 FSR. If you run a motor inverted extra nitro 15% to 20% can help make the idle more reliable when on long finals.

Once you motor is tuned you shouldn't have to adjust your settings unless there is an enormous change in temp and R/H or you change your fuel brew. However glow plugs fail, (particularly with new motors being run in), fuel lines split, leaks may develop, etc, etc.

You have excellent advice already but there isn't any substitution for having experienced assistance in setting up your motor's high speed and idle needles for powerful and reliable running with smooth transition. A demonstration is worth many thousands of words particularly in ensuring you don't end up too lean[&o].

If you go to the engine and fuels forum and type "pinch test", (nothing to do with weight loss or BMIs), in the search facility you will see numerous ways of setting up from running in to pylon racing.

Cheers,

Colin

In my opinion 25% nitro is too high for that engine. That's more of a racing fuel where you need to get the absolute maximum power out of an engine. Running an engine on a high nitro fuel quite often means having to continue with high nitro.

Higher nitro content increases power, but also increases the heat generated by the engine, as well as increasing engine wear. It will also increase the amount of fuel you burn.

A 40 size engine should not need more than 10%.
Dennis-

Hi!
Running as much as 25 % nitro in a sport engine is inviting trouble (to high combustion temperature due to the high percentage of nitro)
Use 5-10% nitro and your engine will run perfect! And a OS 8 or Enya 3 glowplug.
Setting the highspeed needle is the same as running the engine at fullthrottle...and at the same time... leaning the mixture out to max rpm (this way you should never fly because of problem with engine leaning out due to reduced fuel pressure when the tank empties).
A rewcounter (Tach)is very seldom needed for setting an engine be it sport or racing...learning to set an engine you do by ear! That's how we do it in pylonracing! And I thing most competitors do it.
Regards!
Jan K
Sweden

Actually I'd have to disagree... In ALL the tests I've ever performed, running higher nitro content ALWAYS results in a cooler engine... Your absolutely correct about needing more fuel though... Which is precisely why it runs cooler.. The more nitro in the fuel, the richer you have to run it... That means more fuel moving through your engine which means the heat is displaced quicker.. Not to mention more lubrication for the engine... The ONLY time running higher nitro content will cause you a problem is if your using an engine from across the pond.. Those UK engines aren't designed for much nitro, so they have much higher compression ratios... That can mean pre-detonation with higher nitro content... I use 30% heli fuel in all my engines and get many YEARS out of engines without so much as a new piston or sleeve... It should be pointed out however... Running an engine too lean on higher nitro could cause more problems than running an engine too lean with lesser nitro...

I would recommend you get a jug of 5% fuel and mix it 50/50 with yours. This will give you 15% as a result. Be sure to use clean and dry containers and keep lids tight to keep moisture out. Buy 10 or 15% in the future. The higher nitro MAY be making your needle setting more critical but I won't swear to that. Hopefully you have not fiddled with the "idle" mixture since all was running OK. If not, you should be able to quickly get back in tune, especially with a little experienced hope. BTW, most trainers don't need to be tweaked to the max, just close. You're not racing and probably flying reduced throttle most of the time anyway. Stick with it.

Thanks everybody for the responses to my questions! I really appreciate the help! As a side note....today I went into a hobby store in Salt Lake City and was a bit overwhelmed by all the stuff! There was everything and anything a guy could want for his RC! It was kind of one of those things where there is too much to look at and too many options. Wow! Thanks again!

Hello!
Well, too much nitro in an engine not made for "high" nitro contents will only make it produce less power, due to the wrong compression ratio.
Nearly all sport engines are "made" / set-up, to "like" 0-15% nitro, this is a well known fact among every flier that has been around for some time.[>:]
In Formula 1 pylon 10 years ago or more, 50-65% nitro was used but this was in engines that had their combustion chambers set up to run on such high nitro percentages.
Over 15% nitro in nearly all sport engines will only make them produce LESS power. That's a well known fact! This due to too high compression inside the combustion chamber.
There are some fourstrokes like the Saito and Y&S that can handle more than 20% nitro but they are the exception to the rule.
Running ordinary OS ,TT or Magnum engines on more than 15% nitro is just waisting money, getting less power and shorter engine life...and probably most important ...risking the aeroplane due to the engine being very hard to set!

Regards!
Jan K
Sweden