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problem with with saito FG 36

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Old 03-18-2012, 04:54 PM
  #1
orthobird
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Default problem with with saito FG 36

I have a dynaflite super decathlon, with saito FG 36
no maiden flight yet,
almost earlier today,
except, engine conked out on runway when i fully accelerated.

i have a problem.

engine has been run in my backyard for over 1 1/2 hours
using 20 to 1 oil mix, as prescribed by Saito.

I was set to fly plane today.

I built cowl with a total of 3 air inlet holes on the cowl front face.
the outlet areas are much larger area thab the three intake holes.




took plane to airfield, turned on engine, and it was revving fine,

i then taxi'ed plane on runway, and walked behind it, warming up engine, and little up and down revving. right before take off, i put full throttle whilst still holding the plane, just to do one last check.
it appeared to hesitate very minimal, once i let go of plane, full throttle, and it began to lose speed and engine almost shut off, i decreased throttle, and

aborted flight.


while cowl was still on, i tested again,

i turned on engine, then began to throttle, and on doing so, it sounded like engine wants to die
if i do not decreased throttle, it would shut off for sure.

i can throttle from iddle to about 1/4 speed, past this, and it wants to die.

i know engine is hot by now

so it sounds to me like there is an issue with airflow in the cowl, or warm air, or turbulunce issues.


does anyone have any suggestions???

i do not want to fly plane with out the cowl.

if the cowl is off, the engine runs fine
and i can get 7800 rpm with a 18 x 8 prop


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Old 03-18-2012, 05:21 PM
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Default RE: problem with with saito FG 36

You need to baffle the engine so that the air that comes into the cowl flows through the fins. The air will take the easiest way out of the cowl, if that is down in front of the engine without going through the fins it's going to continue to overheat.
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Old 03-18-2012, 05:32 PM
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Default RE: problem with with saito FG 36

the motor is mounted not upright or inverted 
but with the cylinder head out to the right of the plane, and it is not within the cowl.
so the cylinder head and its fins are not in the cowl'

let me see if i can attach  a picture
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Old 03-18-2012, 05:45 PM
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Default RE: problem with with saito FG 36

here are the pics

any help would be great
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Old 03-18-2012, 05:57 PM
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Default RE: problem with with saito FG 36

That sounds like the carb needs adjusting.
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Old 03-19-2012, 03:35 PM
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Default RE: problem with with saito FG 36

update

i opened the three front openings up more on the cowl
then i made 4 small holes on the top of cowl, where i could see the high speed needle and use a special thin screwdriver, with which
i could adjust HSN with engine and cowl on.

took plane to my back yard, this time, with cowl still on.

turned engine on, and was able to run it for about 20 minutes, no conking out
however
i did have to richen the flow of gas by about 1 1/2 turns
and then it had power
i got 7950 rpm with a 18 x 8 master airscrew prop

the only thing is that once in a while, it would hiccup, but would not turn off.

i wonder if i need to make an airscoop that will flow air near to carb opening?
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Old 03-19-2012, 06:32 PM
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Default RE: problem with with saito FG 36

Looking at the front of the plane there is insuffiicent exit holes (meant to be at least 2 times the size of the air entry holes. However, I'm assuming that the cowl opens at the back (at the bottom) for cooling. Apart from that, the cylinder should be getting enough air.

It sounds like the tuning is not quite there yet. You may have to take the cowl off to access the low needle. A quarter turn richer on the low should enable you to lean out the top end a few more clicks without risking the engine quitting.

Try holding the engine up to the sky and tune it to run at WOT and idle. You should be able to get it to run reliably using this tuning method. Don't worry about the odd burp, the engine needs a few hours before you can nail down the exact tuning.
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Old 03-19-2012, 06:45 PM
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Default RE: problem with with saito FG 36

here are two youtube videos of when engine ran today:


http://www.youtube.com/watch?v=6ChTLNYWHdI

http://www.youtube.com/watch?v=gSPlhfCDXWc
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Old 03-19-2012, 07:11 PM
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Default RE: problem with with saito FG 36

in and out of cowl pics
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Old 03-25-2012, 04:01 PM
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Default RE: problem with with saito FG 36

update, flew the plane today,
the engine did great
had a 18 x 8 nylon prop
prior to flight, it was a warmer day than any other day i had the plane,
i made the gas flow richer again by 1/2 turn
got 7800 rpm on the tach

whole flight, not a single problem with engine
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