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engine quits after half throttle

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Old 11-25-2010, 01:53 AM
  #1
varun3d
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Default engine quits after half throttle

Dear Friends,

I am flying Gas planes since the last two years upto 170 cc. Recently i bought dle 55 engine and was performing excellent . I have done more than 80 flight and lots of hover and the engine gave me no trouble. Suddenly two weeks back while i was hovering ,the engine started losing power and I was lucky to get away with just a damaged landing Gear on my CAARF YAK 55 sp.

I then tried starting it on the ground the following was the trouble with engine.
- It works ok till half throttle as soon as i increase beyond half throttle the RPM starts reducing and the engine cuts off, as if not getting any fuel. My engine Has 2 filters one on the filler and one between carbourettor and tank.
Also i have two fuel filters on my fuel filling caddy.

I have tried the following as well:
1) I checked tank and fuel flow to carb - it was ok
2) changed plug and checked current -it was ok.
3) I tried to open needle - no improvement
4)I changed ignition battery pack- no improvement
5)I opened fuel filter in carbourettor no dust was found. I have a spare carbourettor of Wilbro i Changed it but problem still persists.
6)I have a spare ignition unit i tried that as well problem still persisits.

Now i am really in a fix. Please let me know and help me with what i need to do further.It will be a great help to me Engine just doesnt come to full rpm.
I might take time to reply as i am travelling to Uae for the Uae Top jet meet .I will reply as soon as i can.

Regards
Varun

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Old 11-25-2010, 08:00 AM
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Default RE: engine quits after half throttle

is there a kill switch of some sort in this system?
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Old 11-25-2010, 09:28 AM
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Default RE: engine quits after half throttle

Also take out your needles and blow out the fuel passages with compressed air, the high speed circuit may be plugged.
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Old 11-25-2010, 09:46 AM
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Default RE: engine quits after half throttle

Could be the fuel pump in the carburetor isn't working. Check the pulse port for obstructions or leaks (or the pulse line for leaks if it has a line rather than a port).

Could be a bad pump diaphragm, even in both carburetors. Check to see if the check valve flappers are flat.

JD
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Old 11-25-2010, 10:22 AM
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Default RE: engine quits after half throttle

If it just started, maybe there is some trash in the carb...Also try some fresh fuel. It could have a leak at the carb to engine gasket..Try sprayin some carb cleaner in this area while it's runnin, if it has a leak there, it will show up by varying rpm.....
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Old 11-25-2010, 11:45 AM
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Default RE: engine quits after half throttle

For what ever reason, your results are typical of a walbro carb running on suction, i.e. the pump has quit.
Causes are many so check all lines and pump ports and check for a failed pump diaphram in the carb.
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Old 11-25-2010, 11:53 AM
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Default RE: engine quits after half throttle

Goes along pretty good with a blocked high speed circuit as well. Something rather common with a lot of DLE carbs.
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Old 11-25-2010, 02:11 PM
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Default RE: engine quits after half throttle

Since the carb was exchanged, I think it is the lack of pumping pulse to the carb. Shifted manifold gasket or leaking pulse line etc.
OTOH,
The ignition may have embarqued on the long journey.
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Old 11-25-2010, 02:17 PM
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Default RE: engine quits after half throttle

Pe I missed that he tried another carb. He did try another ignition as well though so we are even. I am with you now with it being a pulse problem, it is about all that is left. Of course there is the unseen like a gasket installed wrong etc. that we don't know about. Sometimes I am amazed as to what it turns out to be.
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Old 11-25-2010, 02:37 PM
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Default RE: engine quits after half throttle


Quote:
ORIGINAL: Super08

Pe I missed that he tried another carb. He did try another ignition as well though so we are even. I am with you now with it being a pulse problem, it is about all that is left. Of course there is the unseen like a gasket installed wrong etc. that we don't know about. Sometimes I am amazed as to what it turns out to be.
Or the replacement carb being a used one
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Old 11-25-2010, 02:46 PM
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Default RE: engine quits after half throttle

Could also be something like the seals are gone in the bearings, but that is usually a gradual thing that is noticed by a need to re-tune the engine repeatedly as it keeps changing after it ran for a long time with no need for tuning.
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Old 11-25-2010, 08:51 PM
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Default RE: engine quits after half throttle

I would have said carb regulator, the symptom is similar to what I saw last summer on my engine. But you already changed that. My carb regulator was fuel starving the engine. Tweeking the fork fixed it. But in this case, maybe an airleak in the case someplace. Earlier this summer I witnessed a DA50 that suddenly lost power (didnt die) but didnt have enough power to make it back to the runway. Some cylinder head bolts broke. Maybe a reed problem. I have seen a DL50 down on power due to what we think was a crankcase leak. After he fixed that it was back to its original power.
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Old 11-25-2010, 11:59 PM
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Default RE: engine quits after half throttle

WHen he had the initial problem the engine could have been seizing and the piston ring now stuck and damage to the cylinder. They will at times start cold and get worse with heat. IF this is the problem it could have caused by poor oil mix or too lean of a throttle setting.
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Old 11-28-2010, 11:15 AM
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Default RE: engine quits after half throttle

Thank you so much friends for the support.
I have just reached al ain Abu dhabhi for the Uae top jet meet. The weather and the field are fantastic.
Will try to send all of you some nice pictures once i reach home next week on the 8th.
As of now i am not with the the engine . I will try all your valuable inputs once i reach home and am with the engine.
Please be a little patient with me.

Thank you everyone really appreciate the valuable feed back.
Regards
Varun Gajjar

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Old 11-28-2010, 11:23 AM
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Default RE: engine quits after half throttle

This is a great time of year for weather in Abu Daubi. Enjoy the meet!
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Old 12-24-2010, 04:45 AM
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varun3d
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Default RE: engine quits after half throttle

Thank you everyone for so much help and support. I did put the engine on the test bench after cleaning all the needles and passages.
The result was the same . So now i have ordered the spare parts. I also have another 50 cc from Da i am facing similiar problems. So i will have to wait till i change the pump.


Thank you everyone for the valuable suggestions and help.I will get back in 15 days time once the spare parts arrive(customs).
I really appreciate the help without which i could not have understood this problem.

Merry christmas and a happy new year in advance.

Regards,
Varun
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Old 12-24-2010, 07:59 AM
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Default RE: engine quits after half throttle

I think it is a good time to remove the cylinder (4 bolts) & check everything inside. Look for parts installed wrong...ect. Take intake manifold apart & check that too. Good time also to see any damage or burrs that should not be there. Best of luck with engine. Have a Merry Xmas too. Capt,n P.S Check the timing!
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Old 12-24-2010, 10:21 AM
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Default RE: engine quits after half throttle

I am thinking either a pin hole or other air leak in the fuel lines somewhere, or an air leak (vacuum) somewhere on the engine. Reed block not sealing, crankshaft seals, leaking cylinder base gasket, something like that. This is assuming the other carburetor tried was a good one.

Check the fuel screen in both carbs again, and both the regulator and fuel pump diaphragms. Stiff regulator or distended fuel pump diaphragms can cause this...

AV8TOR
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