bob8619

Saito FA91 engine and this is how I've been doing it. I start it out rich and then with my GloBee tachometer I lean it out until it reaches max rpm and then richen it back out til it drops a few hundred RPM. The tach jumps around so I dont know how accurate this is plus when I richen it up to a good RPM its smoking like crazy so to me I would think this is too rich. This engine is pretty easy to tell by ear when its really rippin which I would assume is the highest rpm making that sound, so cant I just get it to that point then make it a little rich from there?

Gray Beard

My Feedback: (-1)

Yes, most all of them. I have a couple of YS four strokes {older 1.20s} that you can't hear when they rise or fall from MAX to a few hundred. My OS engines and the saito's I have always been able to hear and tune by ear. I use a TNC tach but I have it because I tune so many different types and makes of engines, gas and glow so I spent the money. I tossed my Globee and GP tachs because they were total junk.
I have found the one that Horizon sells as a combo, tach and volt meter that is a very good unit and measures up with my TNC. I have checked over a half dozen of them. I think it is by ACE?

AmishWarlord

My Feedback: (5)

Leaning to max rpm on a 4-stroke may put it over it's red line.

Use the tack then back off 500 rpm for unloading in the air.

If the engine is rated for 12,500 max rpm,

and you lean it out to 13,200 RPM on the ground,

Then fly it at 13,900 RPM in the air.

You will be on here wanted to know why your engine overheats and goes dead stick after a few minuets flying.

Then you'll probably be posting that the brand of motor you bought is crap, over heats, and cost you your plane by going dead stick so don't buy one.

Remember you stepped up to a higher class of motor so you need to increase your operating knowledge, skills, and tools.

AmishWarlord

My Feedback: (5)

So that TNC is worth the price Gray Beard? I have the Glowbee I use when in direct sun light, otherwise I use a laser tach. I have seen some crazy reading on the Glowbee though.

I'll have to look into upgrading.

ratshooter

I just use the fingers on my left hand. Using my ear sounds like a good way to wacked on the head by the propeller.



Just to be serious tuning by "ear" is all I have ever done.

bob8619

Well the engine max it says is 12000 RPM, I have yet to see my tach read much over 10K - reminder that it jumps around so I dont know what the true rpm is - , I figured 12k may be achieved with a smaller prop and each size prop has its own max and thats what you are to avoid. Maybe I'm wrong. I'm using a 14x6 and the highest I have gotten it was 10 and some change and from there I try to drop it a few hundred rotations.. I know some people just dont have the ear for knowing when it sounds like its spinning faster, I feel I have the ear for it because its obvious when I lean it out eventually it speeds up more and more until it just levels out, at this point I richen it up a bit.

blvdbuzzard

It appears I have been doing it all wrong for all of these years? I have not used a tach to set any of my engines. I have not blown them up or burned them up from a lean run. My Saito, YS, OS, Magnum engines have run well for me.

I have watched guys set theirs with a tach. Seems they used half a tack of fuel tweaking the needles, refilled and almost always had a problem. Seemed they were adjusting a lot more then I was. Then again, I never went for that last 100 or so RPM.


Buzz.

bob8619

I'm sticking to doing it by ear. I'm sure tachs work great for others but not a necessity, I just spoke to my dad as well and he said he never used one for his 4 strokes and never had an issue either. He always tuned mine for me when I was younger (ten+ years ago) and it still runs today.

jester_s1

I've had an OS and a Magnum 4 stroke and I wouldn't be able to hear the 300 rpm recommended drop. I got a tach when i got my first 4 stroke. The other benefit as mentioned above is that you can know for sure you have the engine propped right so you don't float your valves.

On making those cheap tachs work: These optical tachs work the same way chronographs for guns work, and it's common knowledge that you must have a bright white background for that eye to see the bullet against with those. If you are getting erratic readings, try moving to where you can have a light colored painted wall or a white overcast sky for the eye of the tach to see. It will do wonders for the reliability.

bob8619

I was in the garage and at it pointing out toward the bright outdoors and it still jumps. As far as not being able to hear the 300rpm drop, if I over shoot it by making it a little too rich I may lose some power but thats about it. Or will that extra richness damage things?

Mr67Stang

Over rich can cause the engine to stall. Flooded engines can cause a hydrolic lock and break a crank shaft. However, what you are talking about is no problem. I tune on the rich side for engine longevity. If I need more power and I can not get it by changing the prop... I get a bigger engine

acdii

I listen to the exhaust note and can tell when it drops a tiny bit.  I still use a tach to get an idea what the engine is turning, and use it as a baseline.  Unless you have a tach that is hard connected to the engine for a true instant reading, the note of RPM drops is hard to nail down with just the tach.   I tend to run it on the rich side too, better to have it slightly under powered and last forever than to have a screamer that doesn't last long. 

goirish

Gene
Is this the one you are talking about.
http://www.fromeco.org/categories/su...tnc_tachometer

Rodney

Most modelers who have been tuning either 4 or 2 strokes can do quite well without a tack. sure, a tack helps and for some is a necessity but not for all. I'd say 95% of the flyers I have been associated with do not even own a tack and do quite well without it.

AmishWarlord

My Feedback: (5)

OK Now I have a question.

Does the pinch test work on four strokes like it does in two strokes?

guille2006

I do!!!!
It's harder than a 2st cause you need to fine-tune your ear... I'm musician too so no issue with that.
A tach is reccomended as pointed before by others
G.

lopflyers

My Feedback: (12)

What???? Of course not, that is what tachs were made for[X(]. There is this guy at one of the clubs that I go that can, he is old and have being listening to engines for yrs

Gray Beard

My Feedback: (-1)

Yes it is but unless your tuning a lot of different types of engines it is a bit of over kill. I bought mine when I was doing a lot of rebuilding for people and needed to dial them in perfectly and give RPM readings with different props.
I have tested it against a lot of other tachs and that is when I discovered how good the Tach/volt meter combo sold through Horizon is. I have tested against a lot of them and they were all very close to the TNC.
Everyone needs a volt meter so they may as well get a tach at the same time, they come in handy but they aren't a must have item for most sport pilots.
I tune my engines once for the summer heat then once for fall then once during the winter. After living here for 6 years I pretty much know exactly what the difference in my high end needle setting will be from season to season and I don't bother with the tach. If someone else asks me to tune there engine for them then I will pull it out.
When I bought the TNC I was working on more engines in a year then most sport pilots see in a life time.
I have seen better tachs then the TNC but nothing small enough to get into a flight box!!!
Most sport pilots don't need a tach but for those of us that want to know what our engines are doing they are a must. I tune then leave the needles alone, if my engine ran good last week it will run the same way today. Needle twisters drive me crazy just watching them. I have never understood that?

koastrc

One of our members test his tach by pointing at a light bulb, light on. He says the tach reads the RPM of the generator at the power house and the power house RPM is constant. Perhaps that is true. What is true, this guy always seems to be correct in other areas. I have never owned one, but have used his.

bob8619

I don't want to create a new thread for this question but I have a rubberish grey muffler extender that slips on the tip of the muffler however no matter what I do it wont stay put. Does anyone know if those are made to work with smaller engines or any tricks on keeping them on? I've tried zip ties of different sizes and hose clamps. Darn thing flies off soon as I hit full throttle.

jester_s1

A fluorescent bulb should read 3600 rpm if the tach is working right. If it jumps around when you do that test you have bad batteries or a bad tach.

bob8619- It's not about the amount of light coming at the tach. It's about the color. Gun chronographs are unreliable on a clear sunny day because the blue sky doesn't give enough contrast. Before you replace your tach, do the light bulb test and then (assuming that checks out) try a plain white board in front of the plane to see if the tach can read the rpm then. I've also noticed with mine that the tach is sensitive to the distance from the prop and which spot on the prop it's aimed at. If I'm off by much it starts jumping around, but once I learned where it likes to be it works fine.

The conversation now has gone to tuning on the rich side just to be safe and not worrying about it. I know plenty of pilots do that and enjoy their planes just fine, but I don't see the wisdom in it when it's such a small investment to tune with a tach and get it exactly right. With 4 strokes especially, the range of reliable operation can be rather narrow and a tach makes chasing down a tuning issue so much easier.

bob8619

My tach reads right on 3600 when I put it towards a light. I will try a white board one of these days. I have tried different positions to no avail though.

GaryHarris

I can tune a fish! [&:]

bob8619

Kelly

Below is the process I use, works Everytime! Instuctions below are from the legendary Tim Mills, R.I.P.



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.

Gotta go rest my typing fingers!