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05-07-2013 07:33 PM  6 years ago
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HeliRyan

rrApprentice

Colusa ca

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Os91h backfire
Brand new motor . Broke in Rich.. Running perfect.. Leaned a couple clicks on the high needle .. And son of gun spuddered and I swore it backfired and died.. At the field flying.. Gonna throw in a another glow plug and see what happens.. Nitro gurus chime in at anytime
Thanks
I don't crash, I land at full speed!
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05-07-2013 07:47 PM  6 years ago
Duosport

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Morral, Ohio - USA

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I am no nitro expert by a long shot but only time I had one act like that or run backward I was to lean.
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05-07-2013 07:52 PM  6 years ago
keiser BLADE

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WV USA

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💎Sustaining Member
2nd duosport, I been foolin with nitro for 20 years, since I was 8 years old, being to lean I have had them run backwards. and pop and carry on. im not a expert but I have had my share of tuning. did u happen to put ur finger on the back plate after it came down to see how hot it was?
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05-07-2013 07:55 PM  6 years ago
MartyH

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USA

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Glow plugs do effect the timing so try that with the same needle settings. Make a circuit or two around the field and land and check backplate temp.
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05-07-2013 08:42 PM  6 years ago
VinceY

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Newnan GA

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The last time I heard a heli engine backfire, it turned out not to be a backfire. It was a hole blown in the piston. Sure makes a loud bang!Team Synergy/ Rail Blades
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05-07-2013 09:30 PM  6 years ago
jschenck

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La Vista, NE.

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been my experience when they pop/backfire and run backwards they are too rich on the low end needle settings.

carefully monitor temp. and make sure you don't go lean. One minute lean run can ruin an engine. If you hit throttle hold it should instantly go to idle, good test after hovering for a few minutes. Also good test to do a full throttle climb and hit throttle hold for an auto. It should immediately go to idle. If not high end needle is too lean.

If you pinch the fuel line it should hold the same idle speed for 3-5 seconds before speeding up then shutting down. do this test after hovering it for a minute or two.
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05-08-2013 12:18 AM  6 years ago
HeliRyan

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Colusa ca

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There's a medium and a high needle... Is that what you mean by low medium needle??. If so thank you muchI don't crash, I land at full speed!
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05-08-2013 12:25 AM  6 years ago
jschenck

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La Vista, NE.

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No - tuning the middle/medium needle is a bit different. Idle is the cam adjuster on the carb. high end needle is the one closest to the fuel inlet. the middle needle on 3 needle carbs is a bit different,

start off with factory settings on all three needles. It'll be very rich but it's a good starting point. Read up on the tuning instructions that OS gives, they are good,
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05-08-2013 12:41 AM  6 years ago
HeliRyan

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Colusa ca

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I will give the manual a look over.. There isn't a low needle.. Only a medium and a high... And mixture control screw in between those ..I'll start fresh tomorrow with original needle setting and go from there. Thank you for the adviseI don't crash, I land at full speed!
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05-08-2013 12:54 AM  6 years ago
McKrackin

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Lucasville,Ohio

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May have been fuel pooled up in the exhaust too...POW.....I literally never use the word literally right.
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05-08-2013 01:36 AM  6 years ago
jschenck

rrProfessor

La Vista, NE.

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Idle is not a needle, it's a cam style adjustment on OS engines. I set it to be straight in line with the carb throat (12 o'clock position) and adjust from there. For 15% nitro I might have to go to 12:30. If you think you need to go leaner on idle I'd look elsewhere first. I usually end up at about 1.5 turns out on the high needle give or take a quarter turn based on the fuel and nitro content. Middle range needle usually end up at about one turn out as I remember.

Just don't cook your engine chasing needles. Error on the side of rich. Sometimes you can fool yourself into thinking it's rich when it's actually just slightly lean. Couple more clicks and engine damage has already started. Touching the backplate is a helpful way of knowing if you are in the ball park. If the backplate is cool (and ambient temps are comfortable) then you are likely rich. If it's too hot to hold your finger on you might be too lean. general rule but it'll keep you from roasting an engine. Tuning from there needs to be done flying.
Tuning by backplate temps isn't valid if it's cold outside.

Also keep in mind that the mixture leans out as it gets colder so if you are tuned for 85F outside then you'll need a few click richer when it goes to 50F outside.
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05-08-2013 02:06 AM  6 years ago
dkshema

rrMaster

Cedar Rapids, IA

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For the record ---

Although this is only a "two-needle" OS carb on a 50 SX-Hyper, it is still useful.

The low-speed "needle" or adjustment is the CAM with the screwdriver slot cut into it, to the right of line number 2.

The object on the left having a hex-head is the bolt that retains the brass plate and its built-in rotating brass sleeve with a small slit cut into it. The hex bolt has no effect upon how the motor runs.

In the picture the intersection of line 1 and 2 is also the pivot point of the low-speed needle. It is clear that this adjustment is a cam. You get a 1/4 turn worth of adjustment either way from factory setting.

Factory setting is when the pivot point of the cam is between the cam body itself and the end of the brass cylinder in the center of the plate, and the screw slot aligned with line 1.

Turning the cam causes the brass plate to move in the direction that the cam moves. Turn CW to make the low-speed setting leaner, turn CCW to make the low-speed setting more rich. Never turn the CAM past the limit set by line 2.

If you turn the cam PAST the +/- 1/4 turn of its adjustment range, it puts the cam between its pivot point and the brass cylinder in the center of the plate. Doing so will reverse the effect of turning the cam (makes CCW the leaner setting, and CW the more rich setting). You also run the chance of breaking the cam.

-----

When you introduce the "third" needle into this setup, it becomes the mid-range adjustment.

The needle valve closest to the fuel inlet nipple is the main, or high-speed needle, the small cam is the low-speed adjustment, and the third needle, usually opposite the main needle, on the other side of the brass plate is the mid-range adjustment.

-----

Don't use the low-speed adjustment to set your low-throttle, idle RPM. That is set by how far closed or open the throttle barrel is at idle, and is set either by your throttle trim, or by adjusting the throttle linkage. Set this to keep the motor idling well at a proper RPM.

Adjust the low-speed needle to get a good, clean, and instant transition from idle to full open. If the engine sputters, spits lots of fuel when you suddenly open the throttle, the low-speed setting is too rich. It is also too rich if the engine tends to slow down at idle and finally stop running.

If the motor hesitates briefly as you go from idle to wide open, or if it just plain up and suddenly dies, the low-speed setting is too lean. The motor may also tend to slowly speed up and die while idling if the low-speed needle is too lean.

Adjust the high speed needle to provide good power at full open throttle. Try hovering, then opening the throttle wide open while letting the heli ascend vertically as long as you safely dare. It should continue to pull strongly without sagging, or bogging.

After you get the low-speed, and top-end needles set, you MAY need to tweak the mid-range, if your carb has one.

-----

Backfiring can happen. The OS 50SX-H, if set too rich at startup, or even at idle, was known for its habit of quietly backfiring and reversing direction and continuing to run without a lot of outward indication. Usually, you'd advance the throttle and not much else in the heli would start spinning, as the motor would be running the wrong direction.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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