When I was new and was learning how to tune I found a thread and I saved it in MS word so not to lose it and I keep seeing threads asking how to tune there engines so I thought I would share this because it has worked so well for me.

Dauntae



Here's a scenario: Pilot takes off, plane's engine sounds great. After several minutes of flying, engine seems to lose power, sounds kinda "thin", pilot keeps flying. Engine continues to sag, now full throttle is very weak, pilot now understands that maybe this isn't gonna clear up. Engine dies (what a shock! ), pilot calls for deadstick landing overshoots, tears off landing gear, etc. Never seen this at your field, right?

Here's the way that *I* set mixture on non-airbleed carbed engines (90% of the engines out there fit this category, but the theory is similar for air-bleed carbs). First of all, understand that the high speed needle has its main effect from 3/4 to full throttle, and the low speed needle controls everything from idle up to 3/4 throttle. It thus makes sense to me to spend the biggest majority of my tuning time adjusting the needle that controls the largest portion of engine running, right? Also, remember that there is a proper air to fuel ratio (mixture) that allows the engine to run properly. Too much fuel is rich, and too little fuel is lean. We "richen" the mixture by adding more fuel (turning the needle out, or counter-clockwise), and we "lean the mixture out" by decreasing the fuel (turning the needle valve in, or clockwise).

I start the engine give it full throttle, and lean it to it's highest rpm (peak), then richen it by maybe a quarter turn. Then with the glow plug igniter still attached, I slowly close the throttle to an idle rpm. At the lowest rpm that the engine will still reliably run, I then remove the glow igniter. If the engine dies immediately, I know it's too rich, and I then lean out the LOW SPEED NEEDLE by 1/8th of a turn (don't touch the high speed needle). Start the engine again, (and this is important) give FULL throttle briefly to clear out excess fuel, then slowly close the throttle again. Remove the glow igniter, and this time it may run a little longer before it dies, so lean the low speed another 1/8th turn. Re-fire the engine, give a burst of full throttle to clear it out, and slowly close the throttle again. remove the glow igniter and now notice that the rpm DROPPED a bit when you removed the glow igniter, but the engine kept running. We're getting there. It's still too rich, and you'll prove that by opening up the throttle and hearing the engine "blubber" then die. That's because excess fuel has collected in the crankcase during the rich idle, and when you opened up the throttle, the excess was pulled into the cylinder, making it WAY too rich. Supposed you were on a landing approach, and decided to go around, you throttle up but the engine "blubbers" and then dies (another thing we haven't seen, right?). Yep, the LOW SPEED needle was still too rich, allowing excess fuel to collect in the crankcase, just WAITING on you to try to go around so it could "LOAD UP", blubber, and die!

Keep leaning the low speed needle down until it idles well, but now, when you open up the throttle, it HESITATES instead of BLUBBERS. When this happens, you've lean it down too far, so richen it up 1/16th of a turn and try again. You know you've got the LOW SPEED needle right when you can fire it up, remove the the glow igniter, and the rpm doesn't change AT ALL, and you can open the throttle up, and it doesn't blubber or hesitate, it just runs!

The final thing you do is re-adjust the HIGH SPEED NEEDLE, leaning it to it's highest rpm (peak) and then richening it up maybe 1/8th turn to give it a slightly rich mixture. We also know that the fuel mixture will change in flight when you point the nose up (harder for fuel to travel uphill) and also as the fuel level in the tank changes. In both cases, a leaner mixture results, so we actually need to set the mixture a bit further on the rich side to account for this. While the engine is running at full throttle, CAREFULLY pick the model up and raise the nose to at least a 45 degree angle while listening to the engine. If the engine sags a bit, then you'll need to richen up the high speed needle 1/16th turn. Try it again, and when you can point the nose up and the engine doesn't sag, but maybe shows a slight GAIN in rpm, you know you've got it right.

Now the engine will be happy, and chances are will reward you with reliable running. If you've got one of the few engines with an air bleed adjustment for low speed adjustment, the theory is the same, just refer to your manual to see how to richen and lean the low speed mixture.

I used this as a tuning reference recently and found that it doesn't quite tell the whole story. I think there are a couple of things missing. First of all, when you get idle set how long should it idle for without loading up. I have found that if you tune so you can idle for 30 seconds and then have a clean transition to full throttle you are probably too lean once you get in the air.

Also, running a little rich on the low end may be necessary or better than risking running lean especially if you are doing a lot of verticle type flying. It seems that with my OS and Irvine when I get the transition perfect on the ground they tend to be lean in the air and get to sounding a little thin a low throttle settings. So, I run richer and clear the throttle when on long landing approaches.

I think Dauntae's post is good. No, it can't possibly address every situation, BUT...
It provides a logical process for initial adjustment of any glow engine and this process
is indeed rooted in fact.

It's AFTER this basic process has been accomplished that we can make clear
assessments of what further, "fine-tuning" adjustments are needed. This
fine tuning will be highly engine/prop/fuel/plug/installation dependent. In this
case, no off-the-shelf procedure can replace careful observation and adjustment.

Good stuff Dauntae.

'Race

Thank you RaceCity, It is true that we can't cover every issue with tuning because there are so many different issues with engines running so I find this to be a good basic start to get a engine to run when you know nothing about tuning and you can get it close this way and fine tune it from that point. So if your a Newbie just keep in mind the good point that Rino brings up that this is not a cure all but gives you the basics of how to tune it so you know how to make the finer adjustments when needed.

Keep em flyin
Dauntae

OK lets see if Ive got this understood correctly.

My engine, an OS46 FX, has had about 4 litres of fuel through it now, 1 litre on the ground running smokey rich the rest in flight. Ive set the high end needle valve so that when I reach a peak in RPM, I richen (wind out) it 3-4 clicks. After some difficulties with it spluttering and dieing (always after landing thankfully) after a long idle period, like on an approach, a mate (Vortec) suggested I lean out the idle valve, about 1/8th of a turn, after starting it and running fast for a few seconds I let it idle for about 10-15 secs and it races to life, no spluttering or dieing etc. Which we had to do twice to get it right. BUT if I let it idle for longer, like a minute, opening the throttle quickly produces smoke, noticeable oil/fluid from the exhaust and it splutters away for a few secs before reaching peak RPM. This worries the heck out of me as Ive been practicing my landings doing touch-n-go's. It hasnt yet actually stopped on me though. Today while flying it I noticed an almost complete lack of exhaust smoke and the oil on the tailplane after flight wasnt its usuall greenish colouring, more grey. I immediately thought its too lean. I richened it 2 clicks and after the next flight it was more the usuall greenish colour. BUT after idleing for an approach, the spluttering on applying full power was even worse. In testing on the ground, it takes maybe 10-15 secs to reach its lowest idle RPM after running flat out, then the idleing gets sort of rough, like its missing a bit.
Do I now need to lean out the low end just a fraction so it will idle for a longer period and reliably achieve full power again ? Am I right in assuming the oil on the plane after flight shouldnt be a greyish colouring ?
I hope the above makse sense.

No. For the first few tanks it should be almost black. After that greyish is OK. I suspect you have been running the high speed needle too rich. This is good on a new engine. That would require a richer than normal idle for smooth transition, but as you found out that means it won't idle for long periods without speeding it up. I would suggest buying a tach and riching up the high speed about 300 RPM. You have ran enough fuel through it now to run at a normal slightly rich setting.

HUH, almost black ? ? ? [X(]

I thought if it was black that was really bad when its a new engine ? Its never been black. Apart from the ground running its never made a lot of smoke, especially in flight at full throttle. The only time Ive seen any real amount of smoke was transitioning from idle to full throttle whilst in flight or over the top of a loop, just before throttling back after the engine was loaded up going up into the loop.
I seem to recall reading that when new, it should be smokey for the first half dozen flights or so. Maybe today, with it a slightly greyish colour was OK, I did lean it a click or two before the first flight today but it didnt seem to be running as sweet today as other flights when the oil residue was a greenish colouring. Sort of surging occasionally at full throttle so I thought it was too lean when I saw the greyish colouring. After richening today it seemed much better at full throttle ? I also checked the clunk was in the right spot and not tucked under itself as I had been putting the trainer through its paces, ie multiple rolls, loops, outside loops and snaps or flick rolls, (full back stick and full left rudder gets its spinning round fairly quickly. (for a trainer anyway)
I think I need to lean out the low end mixture a touch maybe a 16th of a turn, the quick pinch test at full throttle shows no or tiny tiny gain in RPM and picking the plane up to a vertical attitude shows no gain or drop in RPM. After starting and running quickly to full throttle then back to idle, let it idle down to lowest RPM and remove glow ingnitor shows a small, maybe 50 to 100 RPM (guessing, no tach) drop only. I also noticed today that with a full tank, going to full throttle and quickly back to idle thers a tiny amount of fuel gets pushed back up the muffler bleed line, doesnt make it to the muffler, I just see it come up a bit, only at a freshly filled tank, so obviously the pressure is good to the tank, as the quick drop in pressure and flow rate of fuel from the tank has it pushing the fuel out the only other availble outlet.

Another question, how many little bubbles in the fuel line from needle to carb is bad ? I see the odd little tiny ones from time to time at idle but it doesnt seem to make any noticeable difference, at full throttle theres a few but again no noticable difference in performance. These are possibly coming from the tank but I cant see them in the green tubing only in the clear from needle to carb. Maybe I should change the tubing to ALL green then I wont see them and worry about them.

I didn't catch this at first, but if you have greenish oil you are probably using Coolpoweer which has no castor. That is why you have little smoke. The FX should have some castor oil in the mix. Yes for the first few tanks the oil should have been almost black. This is the aluminum wearing off the piston. Once broken in (like several gallons) the oil may be clear (but maybe not due to castor varnish in the muffler), but till then slightly grey is normal.

The first litre was a castor oil/synthetic mix 0% nitro fuel, now 5% nitro Coolpower, or Australian hobby distributors synthetic oil equivalent from a hobby shop. It was all he (guy in my town, new shop) had in stock other than 2 litres of something he'd mixed himself that was clear, he claimed it had a synthetic/castor mix but was not labeled and he didnt seem sure what it was. Not my regular LHS either so I didnt get it. Ill buy from my regular well stock hobby store in the next town from now on though, he mixes what you want but usually has a 15% synthetic 5% castor blend ready to go.(IIRC) Ill go with a 5% nitro added to his normal brew next time I think. Im NOT getting into this castor or no castor debate though, Ive read all the threads on it and it seems 100% of people will have they're own opinion on it, some swear by castor oil blends, others by synthetic only blends. I will say the synthetic only is easy to clean up though.

Doesn't that tell you something? I mean which is easier to clean off the floor, 90 Wt gear oil, or 5W motor oil? Which will do a better job of protecting metal?

Lancair....pop down to your local Castrol agent and get some Castrol M, it's the best castor money can buy. And Cruel Power most definitely needs added oil

Hi!
Oil coming out of the silencer should always be clean...never gray!
Black it could be if you run a pipe and use 20% castor oil or if you race your engine in sport Q-500 racing with a Webra GT .40 running on 80/20 FAI fuel (castor oil).
But never gray or black if you run synthetic oil.
A gray colour always means that there is metal particles in the exhaust oil....No good!

Regards!
Jan K
Sweden

One other thing I have noticed some of my fellow flyers not doing is ADJUSTING THE SERVO THROW for the low end on the throttle. It usually only happens when a new engine is placed in a plane or the same one has been been removed and some kind of maintenance done. A lot of people take it for granted that once you manually adjust the closure of the carb before firing the engine up, that everything remains the same in the low end. Not so. If the engine low end is adjusted to around peak, the idle can increase to a point that you need to close the carb some more to bring it down. The only way to take care of the high idle at that point is to close the carb some using the throw adjustment on your TX. People forget about this factor.

Another factor is that some peple will never lear how to adjust carbs right no matter how much you show them. For them it stays a mystery. For others...its fun and quite fast and easy! Capt,n

So how do you get someone to actually listen and understand these instructions? When I try to explain this procedure to folks at the field who are having trouble I get nowhere. If I tune their engine for them they are very appreciative and seem to understand, but they next time they show up at the field they will not do it themselves. I feel like I'm talking to a wooden post.

This thread last saw traffic in June 2004...

Talking about revival...

Wow I barely remember posting this back then, I'll have to resave this, that was about 3 computers ago lol

Dauntae