Gas engine tuning for newbies....

[Izzy]

	Quote: Originally Posted by mfuess
	Greetings IZZY, Yes, our web server is down and should "hopefully" be back up sometime today. The factory settings from DA are often close to a perfect tune. I'm sure your engine is fine but you still need to keep a watchful eye on your tune as it breaks-in. If it starts easy and you get clean throttle with minimal "four stroking" I would leave it alone. One thing about a DA-50 is, they are rarely (if ever) out of tune from the factory. Desert Aircraft does a supreme job making sure their engines are setup properly and your engine may only need the slightest fine adjustments as it breaks-in. You will have to "tweak" your tune slightly when you switch to the 100:1. In my "humble" opinion, the DA-50 is the finest 50cc engine available. I have yet to see one needing a major re-tune.

Thanks a ton for the quick reply. the DA is four stroking because I started to tune it with your method, but stopped when I remembered that the tune would change when switching the mixture, and then left it a bit rich just in case. should I retune for peak performance while breaking in?

Thanks again,

Izzy

[mfuess]

I wouldn't... Let her break in a bit and enjoy the power of your DA-50!

[mfuess]

When you tune, make small adjustments and only one needle at a time. IE: If you suspect your lowend may need tweaking, turn the lowend needle (either way) in increments of about 1/60th of a rotation. I call them minutes. 5 minutes is about the width of a screwdriver blade. When you approach peak tune, (both high & low) small adjustments make a big difference in performance.

[Izzy]

Hey Mark, how long should I wait on a new engine to use your tuning method? I have about 2 gallons through mine now on 32:1 lawnboy ashless

[airriley]

Wow, I am surprised to read the bit about the DA-50 being near perfect tune from the factory. In the last 3 months I have witnessed 3 new DA-50's at our field. Two of them mine and one a buddy's. All required serious leaning on the low end, somewhere between 1/4 and 1/2 turn. I run mine on 40 to 1 Penzoil, not really sure what my buddy uses. What gives ?

[mfuess]

	Quote: Originally Posted by airriley
	Wow, I am surprised to read the bit about the DA-50 being near perfect tune from the factory. In the last 3 months I have witnessed 3 new DA-50's at our field. Two of them mine and one a buddy's. All required serious leaning on the low end, somewhere between 1/4 and 1/2 turn. I run mine on 40 to 1 Penzoil, not really sure what my buddy uses. What gives ?

Probably luck of the draw & evevation. New engines are somewhat sensitive until the ring seats and adding environment to the equation often changes the pre-set. 1/4 to 1/2 turn on the lowend isn't anything to lose sleep over. I use Penzoil 40:1 also, and I never bothered to switch to 100:1 inspite DA's recommentation.

[Izzy]

Hey Mark, Just got done trying your method to tune the DA and I have a bit of a problem. after setting for peak RPMs and beginning to adjust the LE needle to stop four cycling until idle, I begin to open up the LE again whenever the engine starts to bog down when going to full throttle. My problem is that I can't seem to get rid of the 4-cycling without going too lean on the engine. as I have it right now it takes a bit of time to start (which makes sense) and I have to warm it up for about a minute before increasing the trhottle, otherwise the engine stops. It still 4-cycles at about 25% throttle. is it still too lean? I richened it up since I had a deadstick when going from idle to full to pull out of a hover (doing it high to test the needles and such).

Thanks a ton,
Izzy

[mfuess]

Izzy,

Sometimes it's extremely difficult to totally eliminate four stroking because of exactly what you describbed. When you eliminate the four stroking and you give it fast throttle it goes momentarily lean.

Try this Izzy,
Fire up your engine & let it warm up. Go back to the throttle position where it "four strokes". Then, begin to completely CLOSE of your highend needle. IF the four stroking goes away, this tells you that your float valve setting is a little too high or your float diaphragm is a little too stiff. IF it does not change the four stroking, you have a leak somewhere...
Your engine should run perfectly on the lowend needle up to about 3000 RPM (give or take a little) with the highend needle totally closed. IF it doesn't... it's time to pull the carb and give it a good clean up.

[BuzzardChaser]

Hello Mark,
I have a Composite arf 2.6 meter with a BME 115 with cans (see attached photos). My problem is every time I do a Knife Edge or go inverted the engine drops rpm.
Things I’ve done to try and correct:
1. Ported a line from the carb housing into the planes fuse (see nipple on carb) with no difference in engine performance.
2. Cupped the hole in the exterior of the cowl under the carb (see photo) with temporary balsa to prevent any airflow problems into the carb. No difference at all.
3. Sealed it completely and same thing, no difference in performance.
4. Check for any air in my lines.
Engine has about 5 gals now and otherwise is running really good and strong. No hesitation anywhere with good transition to WOT @ about 6700rpm. Starts good too.
Problem seems to get better as I richen the high needle. Can you help me?
Thanks!!

[mfuess]

BuzzardChaser,

Based on what you've describbed and tried, It appears that you may have a hostile engine environment. BUT, this needs to be proven. In order to determine this, you will have to FLY the aircraft one time WITHOUT the cowling on.

Here's what you will look for while flying without the cowling:

IF there's no change as you describbed: THEN, you don't have a hostile engine environment and the problem is within the engine/carb setup.

IF the problem you describbed goes away: THEN, you do have a hostile engine environment and the problem can be easily corrected.

Let me know what it does, and I will walk you through a fix for it...

[BuzzardChaser]

Will try that and report back.
Thanks

[TrikeFlyer]

How many air bubbles are allowable in the fuel line???

When I rev my 26cc to full RPM the fuel line gets full of bubbles. Checked for air leaks in fuel line, filter etc and can't find any. Fuel tank is tie wrapped directly to plywood platform under wing joiner tube.

It is aquare. At lower RPM fuel in tank looks OK, but when rev it up it looks like it is boiling . Would a round tank be less suceptable to vibration that a square tank???

What do you suggets.

[Sired by Fire]

I would secure the tank with velcro and use 1/2' soft foam rubber under the tank. i originally used ties on my tank and it transferred the motor vibration directly to the tank, creating tons of foam and bubbles in my lines, with velcro no vibration transfer and no bubbles. also you have the added benefit of removal over and over, no cutting ties to get at things.

[TrikeFlyer]

Thanks, I will triy some velcro saps , not too tight with foam in between plywood shelf and tank and see what happens.

[mfuess]

	Quote: Originally Posted by TrikeFlyer
	How many air bubbles are allowable in the fuel line??? When I rev my 26cc to full RPM the fuel line gets full of bubbles. Checked for air leaks in fuel line, filter etc and can't find any. Fuel tank is tie wrapped directly to plywood platform under wing joiner tube. It is aquare. At lower RPM fuel in tank looks OK, but when rev it up it looks like it is boiling . Would a round tank be less suceptable to vibration that a square tank??? What do you suggets.

Virtually all single cylinder gas engines generate vibration, and this will reap havoc on anything mounted too tight to the fuselage. Especially gas tanks & receivers. You must soft-mount these items.