There are some of us that haven't aquired the knowledge yet of how to tune your engine. I'm thinking of the "what do I do" when said engine has rpm/sound/action. For example, what do you adjust if when your bump the throttle to full and the engine just dies? Or it chokes and then hits full. Or, when it hits full it dies. Sorta like a cause/effect/fix type list....

Cause...engine lowers rpm and almost quits and then gains full rpm
Reason...low end/idle needle valve too rich
Fix...turn engine off, turn in (close) low idle needle 1/8 turn and restart engine and try transition.



Checks....pinch fuel pickup line to high needle (what does this check?) etc.

at full throttle, pick up plane and hold verticle, does engine sag or quit?

For us newer guys, having a list attached to field box may alleviate problems of what to do rather than going mindlessly into the dark side of engine tuning. Plus it would help speed up the learning process.


Dave...

set the high speed first, Have a devise to hold the plane. Start up the plane. set up to full throttle turn in high speed needle valve slowly to lean mixture until peak rpm is reached. Turn high speed needle back now 3-4 clicks to richen and leave there. Put engine at idle. adjust radio trim to good idle speed. Let sit and idle for 30 seconds and accel to full throttle. If the engine smokes alot and stutters the low end is to rich. If it is to lean the engine will not idle that 30 sec and will run out of fuel. Adjustment for low end depends on the carb design and wether or not it uses a small vacuum port in the front. now the engine should idle and accel and hold wide open throttle. Pick the plane up and hold to full vertical if the plane bogs down on accel it porbably needs a click or 2 of high speed needle richening. This method is usually the easiest to do. Piching the lines really needs a keen ear and full understanding. The theory is at what ever speed say idle pinch off the fuel feed line, if the engine shuts off quickly with out a rpm increase it is to lean. If you pinch it off and it takes a long time to increase rpm then shut off it is to rich. What you want is a second or two delay a small rpm increase then the engine to shut off. brenden

tune the engine after it has warmed.
once the engine has been set, you shouldn't have to mess with the setting
that much. tweaking with the needles all the time is just asking for trouble.

you must compensate for altitude. richer on the ground .....
hold the nose up and tune, then back out the needle around 1/4 trun
a buddie holding the TX is very helpful..better yet, let him hold the plane nose up

i personnally always stand behind the prop or the plane.
use a steak or a device to hold the plane back
NEVER reach over the prop..common sense would also tell you not to
tune the LSN while the prop is spinning...

you must also compensate for weather conditions.
denser cold air require more fuel or a richer setting...

a smoke trail is healthy..but don't be fooled, a too lean or too hot engine
will also smoke.

you can also try using a different temperature glow plug to better suit your needs.

it takes time to get use to engine sounds or the sounds of differnent props.
lower pitch is rich
higher pitch is lean.

seal the engine... backplate, carb, ect.
i sometimes jb weld the carb to the engine on certain engine brands.

loose mounting screws will also make the engine run funnie.
makesure everything is nice and tight.
a balanced prop will help too.

Welcome to the dark side....

Actually, engine tuning is more art than science in the field. In theory it should be more science, but it never seems to work that way.

First off, while both of the above are working along the correct lines, one thing they both said points to one of the problems with general statements about engine tuing.

One guy said to back off 2-3 clicks off of peak rpm. The other said 1/4 turn. Which is right? (2-3 clicks is not a 1/4 turn on most engines).

The answer? Depends on the engine. Some engines have very "peaky" needle valves. You go from too rich to too lean in 2-3 clicks. Most engines are broader than that. So, 2-3 clicks might not be enough back off of peak to avoid being too lean. But a 1/4 turn might be too much. Or vice versa.

What you are really looking for is a small RPM drop off on the rich side. About 500rpm on your typical .40 class two-stroke. But even that number varies from engine to engine, or even prop to prop on the same engine.

That said, the general advice on what is what, and not to mess with your engine every flight is right on.

(Oh, one side note, the pinch test... You don't pinch long enough for the engine to die. You just give a good solid pinch. If the engine picks up RPM, that's good, it's rich. If it drops RPM, that's lean. If you don't notice any change, give a slightly longer pinch, it's probibly right on the boarder line, and needs to richen a little. I use the pinch test on all my planes that I can actually reach the fuel line on. The test works because pinching the fuel line restricts fuel flow, ie, it makes the engine go a little leaner than it's currently set. Once you get practiced at pinching, you can get to be pretty sure of your settings).

And remember, all engines lean out a little bit in the air (or a lot, some engines more than others. Depends on prop, airframe, and other factors).

Don't be afraid of your engine settings. With just a little experience, you'll find it really isn't that big of a deal. Oh, and when in doubt, richen a few clicks.

One other note; in the original post Dave said to "screw in" the low speed needle valve to lean the low end. That's only true of a two (or three) needle engine. An engine with an air bleed carb requires that you turn the low speed needle OUT to lean it.

And I agree with Kirk, engine tuning IS more of an art than a science. And the distinction between what works with one engine versus another isn;t necessarily just between engine brands, the differences are often between two engines of the same make!
Dennis-

Check out this site:

[link]http://www.geocities.com/frieshoo/Hints.htm[/link]

Should help you out.

Andy