It's that season.....everyone has their new toy's they built over the winter and are looking to get out and start flying!

This also brings the reality to most that they need to learn to tune their new engine and there is no such thing as "factory settings" for an RC engine!!

I've posted this in several places around the web and lots of guy's had great results where they were struggling so I wanted to start a thread to be able to easily relay this info:

Here is the process:

Read each step and follow exactly and move the sticks exactly as I indicate, there is no slow stick movement when checking the H and L needles. Since both needles work together, slowly throttling down or up will tell you very little when doing your base needle settings.

Don't omit any steps and don't do any steps out of order and IT WILL WORK, follow each step and do exactly as described:

Basic tuning:

1 - Tune the engine when it is warm, and double check the tune after a flight.

2 - On the Walbro there is a little silver screw on the carb that is an "idle set screw". it has a spring on it and it sets how low the low throttle arm will physically go down. Take that screw OUT and deposit it in the trash can. Do not remove the black H and L screws obviously.

3 - Start the engine and run it for a good few minutes with varied throttle and some full throttle run ups to get it nice and warm.

4 - If you have not done so, adjust the servo travel for a consistent idle, does not need to be perfect as long as it is as low as it will reliably run for at least 10 seconds or so. You can not properly tune the low needle if the idle is too high! For smaller engines set the low as low as it will reliably run and you can adjust after tuning. You will NOT use a high idle setting during tuning as you cannot tell exactly where the low needle is on a high idle. A good low idle should stand still on the ground while idling. An idle up should just make the plane want to roll on the ground.

5 - Tune low needle first. Now run the engine up to clean it out with a couple full throttle run ups and then go to to low idle. Listen to the engine.........how long does it take to start to "load up" or start to slow down in RPM? If it is rough right away you are likely way to rich. Normal starting point on 100cc engines is 1.5L and 1.5H. I have had to go as low as 1 3/8 on the low needle on the Walbro carbs. Adjustments on gas carbs are VERY small, like the width of a screwdriver blade or 1/16th of a turn or less.
A good "safe" tuning on the low needle you should be able to clean it out with some run ups, return to idle and it should have a nice steady low idle for at least 15-20 seconds before it starts to load up. If it does this it is still just a "touch" rich but will not die on you and it will run nice and smooth.

6 - How low should react. Now that you have it running, clean out the engine and let it go to idle. Let it sit for 10 seconds or so and then slam the throttle to full, not slow, nail it!! Listen to what it does. If it dies or almost dies, you are too lean. If it stumbles and works it's way up (may see smoke in exhaust) you are rich. As tuned in number 5 above it should run up quickly with very little or no noticeable stumble.

7 - Now tune the H needle. There are several ways to do this with RPM but the most simple way for a safe needle setting is this. With the engine warm and the low needle tuned run the engine up to full throttle for about 5 seconds. Now chop it in one quick motion to low. Listen to what it does then.
- If it returns to a steady idle, you are very close.
- If the idle goes way low and works it's way up to a steady idle you are too rich.
- If it stays at a high idle and then slows down you are too lean.
- If it dies you are either way too rich or way too lean. With the H at 1.5 (on 100cc engines) you should not be too lean.

8 - When H is set return and double check the L and then double check the H. Then it's time for a flight. Listen to the engine carefully for all of the noted symptoms while you are flying. One engine test I do in-flight is for the H needle. Get the engine nice and hot, maybe a high speed pass or something. Now do a full throttle straight up line. Listen! Engine should be smooth and steady until you can't go higher. If it starts to sag at all, land immediately and richen the H needle just a tad and try it again.
This fade can also be caused from overheating not tuning related so make sure your engine is properly baffled if you now the tuning is correct.

There you go, pretty simple and really only takes a few minutes once you get it down.

Next thing that is dependent on the plane for singles but should be mandatory for twins is baffling. Yes there are those that say "I never baffle and never have an issue". That may be true but your engines are running hotter without question.

The material used is creative foam, also marketed as "Darice foam". It is CA friendly and very easy to work with. I get it here: http://www.amazon.com/gp/product/B00...rch_detailpage

Here is a quick video showing the process. Only takes a few minutes and lowers engine temps drastically for a more consistent tune and longer engine life.

Baffling your engine the easy way!!!! (11 min 53 sec)

Thanks for the info.

Terry,

I'd like to hear your thoughts on baffling for airplanes such as the Aeroplus 111" Edge where the cowl only has 3, small, approximately 1.5" openings for cooling. Some have suggested extra openings in the bottom of the cowl but I'm concerned this will only create extra airflow below the engine and may actually reduce airflow over the top of the cylinders and through the fins. Plus I don't like extra holes unless they are really needed.

I was thinking some 3D printed baffles such as what I've attached should be helpful but not quite sure it will be enough. Something similar with a right angle bend would be placed behind the bottom opening to deflect the air up towards the cylinders..

Thanks for any feedback.

Wayne

I fully believe guys with an ear for music have an easier time at tuning gas engines. I am not that guy. I've been flying gas for close to 10 yrs now and I still struggle. I follow your method Terryscustom to get as close as possible. From there it is little adjustments along the way. In the early days it was very frustrating for me, I don't think I owned an airplane that the landing gear block wasn't ripped out multiple times. My point is to stress the small increments for the beginner when trying to creep up to that sweet spot. thanks for the post.

Hey Terry,

What is the spray you are using and where can it be purchased?

Originally Posted by thurmma

Hey Terry,

What is the spray you are using and where can it be purchased?

It's just aerosol accelerator, I get mine from a company that sells to industry not available over the shelf. It's a lot better to control than the liquid spritzer style accelerator.

Originally Posted by fixedwingonly

I fully believe guys with an ear for music have an easier time at tuning gas engines. I am not that guy. I've been flying gas for close to 10 yrs now and I still struggle. I follow your method Terryscustom to get as close as possible. From there it is little adjustments along the way. In the early days it was very frustrating for me, I don't think I owned an airplane that the landing gear block wasn't ripped out multiple times. My point is to stress the small increments for the beginner when trying to creep up to that sweet spot. thanks for the post.

Never thought of it as music but I think you are correct.

Originally Posted by wfield0455

Terry,

I'd like to hear your thoughts on baffling for airplanes such as the Aeroplus 111" Edge where the cowl only has 3, small, approximately 1.5" openings for cooling. Some have suggested extra openings in the bottom of the cowl but I'm concerned this will only create extra airflow below the engine and may actually reduce airflow over the top of the cylinders and through the fins. Plus I don't like extra holes unless they are really needed.

I was thinking some 3D printed baffles such as what I've attached should be helpful but not quite sure it will be enough. Something similar with a right angle bend would be placed behind the bottom opening to deflect the air up towards the cylinders..

Thanks for any feedback.

Wayne

GHoffman would be the guy to talk to about that, he has experience with the baffles and may have more experience with fluid motion.

Myself, I would try to limit the expansion of the chamber once it goes in. If you can make the surface area of the back side of that baffle very close to the surface area of the inlet you would be fine. Making the backside too much larger will slow the air down. I think they would work though, WAY better than nothing.

I attached a couple pics here of what I did on an EF MXS with a ZDZ90 single installed . I actually aimed the air down at the head of the single and got additional cooling. I used foam, but 3D printer stuff is pretty badass too.

Originally Posted by terryscustom

GHoffman would be the guy to talk to about that, he has experience with the baffles and may have more experience with fluid motion.

Myself, I would try to limit the expansion of the chamber once it goes in. If you can make the surface area of the back side of that baffle very close to the surface area of the inlet you would be fine. Making the backside too much larger will slow the air down. I think they would work though, WAY better than nothing.

I attached a couple pics here of what I did on an EF MXS with a ZDZ90 single installed . I actually aimed the air down at the head of the single and got additional cooling. I used foam, but 3D printer stuff is pretty badass too.

Thanks, that is is exactly the type of info I was looking for.

Wayne

Good advice Terry, thanks for posting! I will be using these steps to get my new DA70 all dialed in (as soon as I get it back from DA)

Glad to see you pointed out that there is no such thing as factory settings for a carb
I have seen so many people that are not engine savvy think that factory settings are the gospel

Initial needle settings are a factory recommended start point - correct tuning is dependent on many factors

Excellent write up/explanation.

One of the best and most informative threads I've read in a while.
Thank you for sharing.