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Old 05-15-2007, 05:44 AM
mfuess is offline
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Doo It! Doo It!
Bedford Texas
Joined Apr 2007
202 Posts
Re: Gas engine tuning for newbies....

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.
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Old 05-16-2007, 08:43 AM
TrikeFlyer is offline
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Joined Feb 2007
95 Posts
Re: Gas engine tuning for newbies....

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.
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Old 05-17-2007, 05:13 AM
mfuess is offline
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Doo It! Doo It!
Bedford Texas
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202 Posts
Re: Gas engine tuning for newbies....

That'll do the trick.
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Old 05-18-2007, 01:23 AM
Izzy is offline
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170 Posts
Re: Gas engine tuning for newbies....

Quote:
Originally Posted by mfuess View Post
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.
Hey Mark, I had another try with the DA. is it possible that it may need a carb cleanup even if it's brand new (3 gallons through it)? I set both needles to 1.5 turns, let the engine warm up, and set the HE for peak rpm (about 7000 on a mejzlik 22x8 at 600ft asl). I made sure it didn't lean out and began to throttle down to tweak out the four stroking. The problem still is that when I close the LE enough to remove the fourstroking the engine hesitates when going from full idle to quick full throttle. it doesn't seem to want to quit (on the ground) but you can hear it doubt for a fraction of a second. richening up the LE a bit seems to take care of the problem, or after a flight the bogging is not there anymore. any ideas?
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Old 05-18-2007, 01:23 AM
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Re: Gas engine tuning for newbies....

by the way Mark, thank you for all of your help
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Old 05-18-2007, 06:47 AM
Dangerous Dan is offline
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United States, TX, Gainesville
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Re: Gas engine tuning for newbies....

Call Keith at BME he woll send you a new carb for the 115
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Old 05-19-2007, 05:21 AM
mfuess is offline
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Doo It! Doo It!
Bedford Texas
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Re: Gas engine tuning for newbies....

Quote:
Originally Posted by israelg48 View Post
Hey Mark, I had another try with the DA. is it possible that it may need a carb cleanup even if it's brand new (3 gallons through it)? I set both needles to 1.5 turns, let the engine warm up, and set the HE for peak rpm (about 7000 on a mejzlik 22x8 at 600ft asl). I made sure it didn't lean out and began to throttle down to tweak out the four stroking. The problem still is that when I close the LE enough to remove the fourstroking the engine hesitates when going from full idle to quick full throttle. it doesn't seem to want to quit (on the ground) but you can hear it doubt for a fraction of a second. richening up the LE a bit seems to take care of the problem, or after a flight the bogging is not there anymore. any ideas?
It sounds as though your float needle may be off slightly to the high side, or your internal filter screen is beginning to get clogged. Your DA really ought to be hitting closer 7200 RPM with a Mejzlik 22x8, that's what I've been getting at 550ft.

You are much better off having it slightly rich on the LE than risking an overly lean throttle up. A typical sign of the internal filter screen getting dirty is; the bogging goes away after the engine warms up, like after a flight.
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Old 05-24-2007, 12:28 PM
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No Matter
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Re: Gas engine tuning for newbies....

mfuess,

Do you care much about plug color?

The reason I ask... I've got a DA-100 that has a new carb and new plugs (about 18 gallons through the motor). I have about 2 gallons through the new plugs. I have a Menz 27x10 turning about 6600 RPM on it, and it can go a little higher if I turn the high needle in more... I'm at 1.5 turns right now.

It's been flying great... lots of power... no sag on uplines... temps are good (no spit sizzle on the heads). I pulled the cowl for a looksie and the plugs are almost white.

I am running H1R oil... would this make a difference in the plug color?
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Old 05-25-2007, 04:53 AM
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Re: Gas engine tuning for newbies....

OverTemp,

Almost white (light grey) is a perfect tune on a two stroke engine. That's very rare to see with a Walbro equipped engine. Congradulations! You've got a 1 in 500 perfect tune. But be careful. When your sparkplug goes to this color, your engine is on the cutting edge of its peak performance. Just keep an eye on it and if you see a change in performance, or engine temperature then open up your needles up ever so slightly.
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Old 06-18-2007, 12:49 PM
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Re: Gas engine tuning for newbies....

Quote:
Originally Posted by Pro1Foam View Post
Fire up the engine and let it warm up. Let's set the top end first since it's the easier of the two. Go to full throttle. Adjust the top end needle for peak RPM. Leave it wide open for about a minute to see if it changes any. Should the engine go lean, open the low end needle slightly
How do you know its gone lean on the top end?
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Old 06-18-2007, 01:03 PM
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Re: Gas engine tuning for newbies....

Quote:
Originally Posted by mfuess View Post
Completely close off the highend and start the engine. Let it warm up, and then throttle up just off idle, maybe 2500/3000 RPM. IF it's "four stroking" try to lean it out "SLIGHTLY". If the "four stroking' does not go away, the Float diaphragm lever is too high, or your check valve is leaking.
If this is true and your engine will run fine with the high-end closed off, then the entire tuning procedure is called into question.

It would make more sense to warm up your engine, close the high end, adjust the low end to eliminate the 4 stroking, then put the high end to 1 1/2 turns and adjust it for max RPM's.

The low end affects the high end but the high end doesn't affect the low end...so tuning the low end first makes more sense.
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Old 06-19-2007, 05:19 AM
mfuess is offline
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Re: Gas engine tuning for newbies....

While it can be done this way, you'll find that it's considerably more difficult. The ideal method is to set both needles to their factory settings and tweak them as needed.
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Old 06-20-2007, 09:13 AM
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Pakistan
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Re: Gas engine tuning for newbies....

Ok, I have one for you guys. My friend's DA 50 was giving him trouble so he sent it in. They changed out the carb among the upgrades and sent it back. Upon return, the engine ran flawlessly for one session. The next weekend, the same old problem came up where the top end is erratic/lean - i.e the engine does not transition properly. This is with the high the high needle at about 2.5 turns and low between 1.5 and 2. With the low at three, it holds top RPM but the then refuses to run at anything lower than half throttle due to an overly rich condition. Can some one walk me through the carb cleaning process - as in what all do you diassemble and what you use to flush it ? Does anyone use carb cleaner and is it recommended ?
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Old 06-20-2007, 09:23 AM
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Re: Gas engine tuning for newbies....

Quote:
Originally Posted by Billa View Post
Ok, I have one for you guys. My friend's DA 50 was giving him trouble so he sent it in. They changed out the carb among the upgrades and sent it back. Upon return, the engine ran flawlessly for one session. The next weekend, the same old problem came up where the top end is erratic/lean - i.e the engine does not transition properly. This is with the high the high needle at about 2.5 turns and low between 1.5 and 2. With the low at three, it holds top RPM but the then refuses to run at anything lower than half throttle due to an overly rich condition. Can some one walk me through the carb cleaning process - as in what all do you diassemble and what you use to flush it ? Does anyone use carb cleaner and is it recommended ?

Pull the front and back plates off the carb and check for diaphram holes and dirt in screens. May as well go to a lawn mower shop and get a rebuid kit if you are going to do that.
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Old 06-20-2007, 11:35 AM
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Kannapolis, North Carolina
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Re: Gas engine tuning for newbies....

billa what ratio of oil are u using and what brand of oil?
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