lokiarf

Need your help! I have a G26 Zenoa engine that runs great on the ground. It will not idle in the air for me. My plane has lost power in eight out of ten flights and was dead stick on landing. If I do acorbatic maneuvers and slow the engine down, it dies. The gas tank is within six inches of the motor with my carberator hooked directly to the tank. There are no air leaks as I have pressure tested the system. The muffler is factory original as well as all the parts. I haven't made any modifications. I use a medium fuel line and a zinger wood 16x6-10 prop. I don't think the fuel system is the problem. I use Amsoil 100:1 fuel. I am a master model builder and believe there's something in the engine causing the problems. Either it's not adjusted correctly or somehting is not right in the engine. How can I solve the problem of keeping the engine running, What is the largest diameter, smallest pitch prop I can run on this engine? So far the best I have found is a 16x6-10. Please give me your take on this.

BobH

My Feedback: (2)

You didn't say if your engine was cowled in or exposed. Proper cooling could be a proplem if its not baffled and its in a cowl. Your servo/throttle linkage could be vibrating and closing the carb too completely. Open your lo and hi speed needle about 1/8 turn each to give a little more fuel in flight so you aren't lean. It's sometimes a trial and error effort to elimenate the root cause but I would try the carb adjustments first and see how it goes.. Regards BobH.

lokiarf

it is in a cowl but has a lot of open air ,,, i have tuned the carb,,its not running hot

blabree

My Feedback: (3)

My Zenoah manual clearly states that the fuel to oil mixture should be 25-40:1 gas to oil. If you are using any other ratio I would suspect a lack of cooling under flight loads and when throttled back to idle the engine sticks and quits. Once dead stick the cooling takes place during the glide to indicate a "not overheated" condition to you on the ground.
I would try a tank or two of 25:1 mixture and see if that fixes the problem. You didnt say how much breaking in the engine has had. Even though the Zenoah owners manual says it is not necessary, there is a "development curve" where the parts are still seating and causing much more friction (heat) that lasts through many hours of initial run in.

blabree

Geistware

My Feedback: (16)

Another recommendation, is to make the exit area twice as large as the entry area. Since the cylinder of my plane hangs down, I have blocked the side entry ports on my extra and it runs cooler with less entry area.

lokiarf

blabree i was running that gas mix but now i use amsoil and it likes it better there is 3 or 4 zenoahs here that run it. it only stops if i snap roll or loop if i fly nice it only quits about 2 feet off the deck while landing

rcpilotjae-RCU

My Feedback: (21)

llokiarf:

From your original post you said you 'pressure tested the system'. You don't use a pressurized tank with a gas engine. Also, on a gas engine it doesn't matter where the fuel tank is located, a gas carb pumps it's own fuel to the engine. Are you running a open vent line out of the fuselage somewhere? Assuming you know all this, then I would suggest that the carb maybe getting a blast of air over it's metering hole (in the carb) and it's upsetting the flow. That can be fixed by a couple of things, one being a cover over the metering hole so the blast of air can't get to it, or solder a tube to the metering hole itself and run it into the fuselage so it see's the same air pressure all the time. This type of engine quiting usually shows up in the maneuvers your describing and also knife edge.

GeraldRosebery

My Feedback: (14)

I also suspect pressure differential between the inlet air and the pump air inlet. This will be especially problematic if the air inlet is through the cowl or outside the cowl and the pump air inlet is inside, in relatively still, higher pressure air. This usually only a problem in flight with the aircraft moving. Snap rolling moves air across the inlet of the carb very quickly lowering the pressure causing leaning condition and an engine stall. The cure is to solder on a small tube to the pump air inlet and make the other end adjacent to the carb air inlet. There was an magazine article I think in Model Airplane News this year on this problem.

R Horn

My Feedback: (2)

GeraldRosebery probly nailed it
Try fly it with out the cowl. If it is good in flight with no cowl you must make a vent for the carbs pump so that it exits the cowl. The easy test is fly it with out cowl.

You can refrence "Model Airplane New Sept 2003 Issue" pg 110
Oh and mix the oil the way the oil manufacturer recomends. Zenoah has there own oil.

Good Luck and let us know.
Rich

lokiarf

rcpilotjae-RCU i dont run pressure but i do fuel by airpressure and my lines hold 25 psi with no leakes i will try the carb vent it may take some time but i will let all who helped know

rcpilotjae-RCU

My Feedback: (21)

lokiarf:

I figured you knew all that, but I do suspect the blast of air over the carb's metering hole is the problem. There are a couple of companies that make pre-made solutions and another that makes a metal flap that goes over the hole (but leaves a space for air) to keep the blast from upsetting the carb's metering of the gas flow.

Here's a quote from Cactus Aviation:
Here's how to add a nipple to the carb's metering plate (the side with the small hole in it on the carb). From Aircraft International...

Now run a length of fuel tubing to the inside of your fuselage or run it to the carb's inlet (that way it 'see's' a constant air pressure).

Or refer to the article in the magazines that others have suggested. Let us know if it solves the problem.

F86_SABRE

Hi,
Is there any chance of viewing the quoted article anywhere? I do not know if this could happen on a Ziroli DC-3 since this is not meant to me tossed around (hopefully!)

Regards

Reuben

rcpilotjae-RCU

My Feedback: (21)

F86_SABRE:

It can happen on any gas engine that uses the standard walbro carburetor. They all have a metering hole. Since I don't think you get the magazines over in your country, here's the web links,

[link]http://www.desertaircraft.com/[/link]

and

[link]http://www.aircraftinternational.com/[/link]

I believe what you want to read is under technical. There are some other sites that explain this and show how to fix it, if I can find one I'll post it here for you.

R Horn

My Feedback: (2)

I can scan this for download if someone wants it. "Model Airplane New Sept 2003 Issue" pg 110 Carburetor Clinic. it shows the solder and brass tube fix

if you choose this fix below or a solder and brass tube make sure you have no internal contact from your soldered on niple that can contact the diaphram under the cover

quote:

For diaphragm coverplates without a pre-installed vent nipple...
- Remove the front plate carefully without removing the diaphragm or gasket
- Degrease the cover plate
- Lightly sand the area near the vent hole with fine sandpaper
- Solder a vent nipple over the hole in the cover plate (same thing as a muffler smoke/pressure nipple)
- Make sure the hole and inside of plate are clear from solder
- Re-install the cover plate.

This link will download a doc made from 3w page on there mod
http://sonic.euriska.com/For%203W%20Motors.doc

I will try and scan the article from Model Airplane News tonight

Rich

R Horn

My Feedback: (2)

Here are the 2 pages from the MAN carb article. Download them then save them and view them with a good picture viewer and you will be able to read and see them clear as day.

http://sonic.euriska.com/MANpg110.jpg
http://sonic.euriska.com/MANpg112.jpg

And a favorite picture viewer of mine ACDSee. this is the classic version runs as shareware

http://sonic.euriska.com/acdseeclassic.exe

Again Good Luck
Rich

lokiarf

hi guys i flew the chip with the tube over the metering hole i had to redo all the carb. set up but it did better i rolled 2 or 3 times did good got cockie did a big slow loop added power and dead stick again but now i think it is just the low side needs a little love thanks for all the help

R Horn

My Feedback: (2)

Cool!