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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › Help needed on firing up a TT39
05-30-2012 12:30 AM  6 years agoPost 41
ShuRugal

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Killeen, TX

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the carb on the TT 39 is extremely hard to get tuned just right. The high end is not too bad, but the low end is exceptionally sensitive to atmospheric conditions.

You probably have yours tuned too rich. The factory settings on this motor are almost too rich for break-in, much less regular flight.

First thing to do is to reset to factory, then start leaning things out. You will need to work with both screws at the same time, but start by adjusting the low-end screw via the pinch method: pinch the fuel line at the carb, if the engine takes more than 5-8 seconds to rev up and die, it is too rich. If it dies in less than 4-5 seconds, it is too lean.

Next you need to get the high-end set to where it will throttle up and down without spluttering out. When you throttle up, if it starts to skip and caugh, then dies, high-speed screw is too rich. If it dies with no warning, it is too lean.

after you perform these two steps, the heli should be making liftoff power. if not, adjust your throttle curves. Mine requires 50-60% throttle at ~5 degrees of pitch to hover in ground effect, but YMMV.

Once you have it hovering for a minute, check the backplate with your (bare) fingertip. you should be able to hold your finger on the backplate for 4-5 seconds before it becomes painful. If less, engine is too lean, if more, engine is too rich.

While performing the backplate test and making adjustments, you will also need to test the response of the engine to *closing* the throttle. To do this, get into a fast hover in idle-up, then hit throttle hold. The engine should immediately begin to drop in RPM, and should settle smoothly into an idle. If the engine wants to stay at full RPM for a second, or if it goes "zing-zing-zing" as it slows down, the high-end is too lean. If it revs down quickly, but then dies instead of going into idle, the low end is too lean.

Once you have it in the ballpark, you will notice that both screws are very sensitive. 1/8 of a turn on the low-speed will take you from too rich to too lean (or vice versa) and any more than 1-2 clicks on the high speed may also reverse your problem.

Also, if you have ever hot-started it, or otherwise burned up a bunch of clutch material all at once, you will need to disassemble the motor, flush it out, flush the muffler, and change the glow plug. Any dust, be it clutch material or clutch bell, that gets on the filament will alter the temperature of the plug and cause trouble. If the motor sucks any dust in, it will collect in the muffler and get re-ingested into the cylinder on every stroke of the piston.

AMA 700159

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05-30-2012 12:04 PM  6 years agoPost 42
helijohn

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UK - Birmingham

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Keep me/us posted.

Grimracer
An update:
I installed the motor and set the carbie as you suggested. It fired and promptly cut. I went to try again and the starter locked up. Yes the fan assembly had come loose and I had used Loctite on the nut. So I have torn it down and reassembled using a high strength threadlock and will try again later.

This engine was assembled at the factory and it has been years since I had to mess with a clutch fan; I can't remember if I added a star washer to get some extra grip.

Why simplify when it's simpler to complicate.

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05-30-2012 06:39 PM  6 years agoPost 43
Grimracer

rrVeteran

Eau Claire WI

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Well.. it was getting fuel then...

Turn the LSN in another turn and try again.

I know this is an odd setup but trust me.. its an eye opener.

Grim

Michael J Zaborowski

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05-31-2012 12:26 PM  6 years agoPost 44
helijohn

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UK - Birmingham

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Another update. Seems like a big fail. I couldn't get it started except one time when it ran for a few seconds and stopped cos stupidly I had shut off the fuel line - dozy or what - and another time when it stopped as soon as I pulled out the glow plug power.

Looks like it is the bin or sale for parts.

Why simplify when it's simpler to complicate.

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05-31-2012 01:01 PM  6 years agoPost 45
ShuRugal

rrKey Veteran

Killeen, TX

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if it stops when you pull glow power, then either the glow plug is bad, or it is still too rich.

AMA 700159

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05-31-2012 01:35 PM  6 years agoPost 46
Grimracer

rrVeteran

Eau Claire WI

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agree,,

I just went thought and broke in a new 39 last night..

Break in needle settings were..

3 turns on the LSN (you can turn this out MAYBE 2 hours but not much more, sorry about the hour crap.. I hang around work with a bunch of car racers and some of the verbage is rubbing off. Hour = 1/12th rotation or 30deg)
5.5 on the HSN

This is a breakin setting.

Grim

Any furter in on the LSN and the motor will go lean regardless of the HSN stetting.

Michael J Zaborowski

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06-17-2012 12:20 AM  6 years agoPost 47
helijohn

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UK - Birmingham

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I got rid of it; just gave up on it.

I bought a used OS32 and it started up relatively painlessly. I'd reset it to factory settings. It ran for about a minute and stopped but after a little tweaking it ran fine. Took it down the backyard to the grass to try it out and it cut out. Tweaked the jets some more and it ran fine, was about to lift off and it cut. Went to tweak the needles some more and found the carbie was loose. One of the screws had come right out and lost in the grass.

I am guessing it worked loose and each time I tweaked the needle it compensated for the air leak until the screw finally fell out.

Here's the good bit, I found the screw in the grass, whacked it back on and the engine ran a treat. When the awful wind and rain stops I can try it again.

Why simplify when it's simpler to complicate.

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06-17-2012 04:46 AM  6 years agoPost 48
ShuRugal

rrKey Veteran

Killeen, TX

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what happened to the 39?

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