Gas engine tuning for newbies....

[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.

[mfuess]

Industrial grade Velcro and or Velcro straps work great. Use foam rubber under your components where possible. I would HIGHLY recommend you look for the source of the vibration. Double check your prop balance, check your spinner also. Vibration is your airplane's WORST ENEMY. Some engines vibrate worse than others especially the budget "imports". If your airplane has a large fuselage the vibration will be absorbed and it will dissipate the energy. Smaller frames will eventually break at the glue joints. Heavy props make matters worse. One thing you DON"T want to do is soft-mount your engine! Your engine needs to be mounted rock-solid to the firewall.

If you have room in your fuselage, move the gas tank over the CG. Move your receiver & battery pack as far back as you can. This will minimize the transfer of vibration.

[TrikeFlyer]

Thanks for the suggestions.

Currently my plane is 69" laser, no spinner, balanced XOAR 17X6 prop, gas tank located back over CG, 26cc single cylinder Chinese engine.

Tank was "hard " mounted to arframe with nylon tie wraps. Removing those and changing to velcro straps with tank on cushion of foam. Changing fuel line to 5/32 tygon, changing to different fuel filter.

Will report back results this weekend.

[mfuess]

That'll do the trick.