orthobird

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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

soarrich

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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.

orthobird

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the motor is mounted not upright or inverted 

orthobird

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here are the pics

any help would be great

soarrich

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That sounds like the carb needs adjusting.

orthobird

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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?

MercerAUST

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.

orthobird

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here are two youtube videos of when engine ran today:

orthobird

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in and out of cowl pics

orthobird

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update, flew the plane today,