orthobird

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hello all,

please help me.

i have a zenoah G38,
the plane has had 5 flights, the first 2 flights were not good, as they resulted in crash.
the first crash resulted in prop damage only.
2nd accident resulted in fuselage and wing damage, and the engine got a bent rotor, fuel nipple fracture, magneto tab (black wire) broken,
everything has been repaired and fixed.

however, engine does not run same as first time,

before, i could get 8000 rpm with an 18 x 8 prop, Zinger.

now engine gets 6500 rpm with same prop and with TWO, then all of a sudden, it will accelerate to 7600 rpm, with me not moving the throtel.

i can get engine to idle at 1500 rpm.

please see these videos i posted on Youtube, so you can see for your self.
thanks for any advice in advance:

http://www.youtube.com/watch?v=6Vu0kbOe4O0

at 17 seconds and again at 30 seconds, you will see it will accel to 7600 rpm, and then back down to 6400 rpm, with carb wide open at all times.



this is a video of it idling at 1500 rpm.

http://www.youtube.com/watch?v=859RkMpE5cA

has anyone seen this before???

what could be the matter??

i have open fuel filter and it is clean, no debris.

orthobird

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[youtube][/youtubehttp://www.youtube.com/watch?v=6Vu0kbOe4O0

w8ye

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The mixture is too lean

orthobird

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update

i opened up LSN

this is result:

http://www.youtube.com/watch?v=J2AK5-dVWrk

captinjohn

Sometimes a bad throttle servo can make the engine sound like that. Maybe it got damaged in the crash. Also check the crankshaft run-out with a dial indicator. The G38 can get knocked out of alighnment easy. Antique can fix em good again. Capt,n

orthobird

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Hi
I have looked at servo and it is not fluttering

I will look into your other suggestion

Thank you

w8ye

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Is it getting air bubbles in the fuel line?

orthobird

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hi
i looked at that also,
in fact, this is the third tank.
it is a dubro 20 ounce tank
sullivan conversion kit
tygon 1/8 " tubing
welded on 1/8 " barbs for brass tubing
there is giant clunk in tank
the clunk and tubing in tank has a clip plus wire tie
there are only two holes into tank, one is vent
the other is fuel line

the fuel line from tank to carb has t shape connector , the part with T has short tube with a cap on it. i use this to refuel tank.

let me know your thoughts

w8ye

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You've tried the needles.

You are not getting bubbles going into the carb

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There may be a problem with the ignition? What about making sure the ignition coil is the thickness of a business card away from the flywheel?

What about the spark plug wire is it shorting against a fin?

Did you change spark plugs?

Is the ignition ground shut off wire shorting against the engine somewhere?

w8ye

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One other thing that may be happening is that air from the prop is blowing across the carb inlet or across the carb vent hole?

orthobird

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oh yes

i noticed that

if i am standing on that side of the plane, i can feel fresh gas land on my legs, it is cool (on the skin), not cool like it is a good thing.

and

i had engine going TWO, and noticed that with the choke valve open, the posterior half of the choke valve, is where the gas is coming out of the carb and out the side of plane.

is this normal??

orthobird

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You are not getting bubbles going into the carb
i checked for this, did not see it.

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There may be a problem with the ignition? What about making sure the ignition coil is the thickness of a business card away from the flywheel?
just checked it, it is, in all 3 points, the center, right, and left side of coil, i can get that in there with minimal binding

What about the spark plug wire is it shorting against a fin? Just checked that, it is not touching anything.

Did you change spark plugs? i have not, but i did check gap, it is 0.025 inch (0.635 mm)

Is the ignition ground shut off wire shorting against the engine somewhere?Nope, checked that also. is the 7500 rpm not good or did you not like the sound of it when you saw todays you tube video?
thanks for all your advice, i appreciate you immensely in trying to help me, God knows i can use all the help.

w8ye

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hold your hand in front of and in behind the carb inlet and see if it makes a difference in the way the engine runs?
Stand behind the engine and do not get your hand in the prop as it plays for keeps!

orthobird

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i noticed that too.
when my hand came near to carb, the engine would idle down.

what does this mean?

w8ye

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You need a velocity stack fastened to the carb inlet to straighten out the air flow going into the carb.

orthobird

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hello everyone,

w8ye

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Good detective work.

A velocity stack would have corrected this without removing the choke plate.

orthobird

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i went online to graves RC and horizon hobby and google,
and could not find one.

any suggestion?

w8ye

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http://www3.towerhobbies.com/cgi-bin...?&I=LXJ775&P=7