Champstarr

Aloha RCUers,

I keep having trouble with my .46 size glow engine on my Avistar Elite. The engine will quit in flight as I advance it to full throttle from half throttle forcing me to dead stick the plane in. I have had this problem in the past but it went away after one of the veteran fliers at my field helped me tune the engine. I make small adjustments to the mixture depending on the conditions but nothing major and for 12 consecutive flights didn't experience this problem. Now it has returned. Any advice is appreciated.

Thanks

Joe Fisher

My Feedback: (4)

You might try adjusting the mixture with the engine running at the part throttle. Peek it out then richen until you can hear a slight drop. Also try replacing the glow plug.

jester_s1

I have a few questions:

How old is your fuel? And how much is left in the jug?

When you pinch test the fuel line with the engine wide open, what happens?

Do you ever see bubbles in your fuel line? How long has it been since the tank was assembled and the lines were run?

Has the engine ever run right consistently? If so, has anything changed since then?

jetmech05

I tune starting with the high end warm the engine then advance the throttle to full. Adjust the the high end so the engine is at peak RPM by ear then richen about a 1/4 turn bring it back to idle and check the low end. Check the low end by pinching the fuel line between the carb and needle valve. The engine should run for a second or 2 before it begins to rev and die. If it dies right away you're too lean. If it runs for awhile before it does anything you're too rich.
the true test let it idle awhile and slowly advance the throttle it should tradition smoothly

Champstarr

Hi Jester,

I bought the fuel the day before I flew.

The tank was assembly was done about 7 months ago. The only time I remember seeing bubbles in the line is when I prime the engine and when I purposely run it through a full tank of nitro on the ground.

The engine did run correctly for 12 consecutive flights. Prior to flying this past weekend I did not fly for approximately 2 months. This 2 month gap is the only change I can really think of prior to that I was flying every weekend.

The engine ran for about 3 seconds when I pinch tested the line.

Hope this helps.

Gray Beard

My Feedback: (-1)

It sounds like the tune is out of adjustment. To give you an idea of how much the temps need to change before you really need to twist a needle. I tune about now for high temps, it's already 110 here. I fly all year long and won't bother touching the high speed needle unless I change to a different prop size or until the temps drop to about 70 degrees. Then it will be about a click at a time until it gets into the 30s and 40s. When I'm finished I will only be about 4 clicks off from summer. The low end almost never needs to be touched.
Moisture / condensation will burn out your fuel but it isn't affected by age. I buy mine in cans and as long as it's lid is tight there is never any moisture getting into it. I also don't live in a moist area so a lot of people in the mid west and east coast are bothered by moisture. Last week our humidity was only at 2% and during the winter during a storm it may get up to the high 20s.
I fly with a new guy to the area and he just got here from Florida and can't get over the fact it's a lot hotter here but doesn't feel near as bad.

A. J. Clark

I like to have the idle set a little on the rich side. I think it helps make a better transition. Second reason is if it goes lean while flying you can pull the throttle back to idle. This will keep it running and cool the engine with a little extra fuel.

jester_s1

2 months is probably not enough time for varnish to have developed in your fuel passage, but it's possible. It's also possible a marginal oring seal has started leaking air too, probably at the carb attachment or backplate. Before looking into that though, make sure you have your HSN set right. You should hear an increase in RPM when you pinch the line. If the engine just dies, you are too lean for flying. Air leaks will show themselves in two ways. The first is that the engine doesn't respond to needle valve changes consistently. The second is mystery deadsticks when you are sure the engine was set rich enough on the ground to run reliably in the air. Other common causes for unreliable engines when you know they are tuned right are bad glow plugs, bad fuel, dirt in the spraybar or needle area, damaged fuel lines, improper tank setup, and a scored or peeled liner.

jaka

Hi!
Some advise!
The center of the tank must be inline with the carb intake orifice when the plane sits level!
And the tank must be as close to the engine as possible.I assume you use exhaust pressure to pressurize the tank?!

Suitable tank size for your engine is 8-10oz. Not any bigger!!!

Suitable prop size for a trainer airplane for your .40 engine is 11x6 if you fly at sea-level.

Suitable fuel contains 5-15% nitro. Everything over 10% is just overkill for the OS engine.

When you set the Engine , as you do before each flight, hold the nose of the plane straight up ...and set thehigh speed needle...then back off some so you hear the engine rpm go down slightly.
Then put the airplane back on the grund and check the low speed. The transition from low to high speed should be instantanius! If not set the low speed needle.
All setting on an engine is done by ear! Not by pinching the fuel line. That metode is just to crude.

Tom Nied

Sounds like my GMS 47's that I never figured out.

Things to try. An OS #8 glow plug, an OS #6 is recommended. Check all screws on the engine making sure they are tight. Is the clunk in the tank free and rattles when the tank is empty and the plane is held nose up vertical? It could be bent forward in the tank. Do the fuel lines fit tight, or are cracked? If so replace. You might want to just rebuild the tank, could be crap in the tank. They take a lot of abuse being pulled on and off each flight. Check the engine mounting bolts, loose engines run lousy. Also you might want to pull up the the exact instructions for that engine and reset the idle needle valve to the default setting and start all over. Just some thoughts.

http://manuals.hobbico.com/osm/46ax2-manual.pdf

tomfiorentino

Champstarr,

Are you saying that this doesn't happen on the ground? The only time it quits upon throttle advance to full is when it is in the air?

Tom

hsukaria

With the engine not running and the fuel tank about empty, hold the plane nose up (vertical) and shake the plane. Make sure you can hear the clunk "clunking" inside the tank.

Here's how many of us tune these engines:
1. Fuel tank 1/4 full.
2. Full throttle, peak the engine by turning in the HSN to get max rpms.
3. Go back down to idle and let idle for about 1 minute (around 2500 rpm), pinch the fuel line. If it quits instantly, open the LSN 1/8 turn. If it runs for a long time and speeds up, close the LSN about 1/8 turn. Repeat until correct.
4. From idle, slam the throttle to full, if the engine quits, the LSN is too lean, open another 1/8 turn. If it hesitates and slowly gets to full throttle, LSN is too rich, close the throttle 1/8 turn. Repeat until correct.
5. Go back to full throttle, and richen the HSN until you hear a drop in speed. If you have access to a tachometer, try to get a 300-500 rpm drop from peak. (edit: you can do this adjustment while holding the plane veritically up.)
6. If this works out, you don't have to touch the LSN unless you get a very big change in temperature, or you change fuel, glow plug type, or prop size. And even then you most likely won't need to touch the LSN once set correctly.
7. If the engine still quits, then you probably have either bad fuel, wrong/bad glow plug, or a leak in your fuel system.