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Thunder Tiger F-91S low speed needle default setting

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Thunder Tiger F-91S low speed needle default setting

Old 03-21-2012, 09:07 AM
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larryoakley
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Default Thunder Tiger F-91S low speed needle default setting

Hi all,
I'm new to this forum but have been nitro flying for years. I have always flown 2 strokes but have just purchased an second hand Thunder Tiger F-91s 4 stroke for the first time trying to start it without success, the user manual mentioned the high speed needle (HSN) default factory setting but not a word about the low speed needle (LSN) default setting, I had to disassemble all the engine in order to clean it and to make sure everything (bearings, o-rings, valve gaps, etc) be OK.

I did some research in google about this LSN matter but there are several versions some indicating that the open number of turns must be done with the throttle completely open and some without any indications regarding the throttle position at the moment of set the opening turns, as you know the tricky part of this needle is the fact that it travels with the throttle barrel, in other words, a completely close LSN depend on the throttle position.

The user manual indicate how to adjust it latter in order to have a smooth low speed to high speed transition and good (slightly rich) idle but of course to reach that point I need to start the engine with the proper settings.

Anybody knows what should be the low speed needle setting as starting point?


Thanks!!!
Old 03-21-2012, 09:31 AM
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jaka
 
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Default RE: Thunder Tiger F-91S low speed needle default setting

Hi!
It's easy!
You just open the low speed needle as much as you want! Start the engine and then set the high speed needle and then... adjust the low speed needle...by ear!!!
Old 03-21-2012, 09:33 AM
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Default RE: Thunder Tiger F-91S low speed needle default setting



You don't need the low speed setting as you need to break in at speed.  If you have an older model you need to attach the carb choke as it won't draw properly without it.  The rings won't seal well at all out of the box, so make sure you have lots of castor before you start it, in fact squirt some in the cylinder before cranking.  Forget about hand starting, the rings may leak too much for that, the carb wont draw fuel for the same reason.  Instead unscrew the glow plug and squirt a bit of fuel into the engine.

The engine has some hard metal in it so it takes a while to break in, I wouldn't bother even thinking about the idle mixture till you have run 3 to 5 tanks of fuel through it.

Old 03-21-2012, 09:57 AM
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larryoakley
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Default RE: Thunder Tiger F-91S low speed needle default setting

Jaka:

Correct me if I am wrong or what but if I fully open the LSN the only way to keep the engine running is at full throttle or at least more than half, so the question is how healthy is to have such amount of RPMs during the break in period


Sport_Pilot:

1) Can you please explain me when you said "you need to break in at speed" since the user manual mention not to go over 5000 RPM during the Break in chapter.

2) How do I know if my engine is older or newer model? mine has the black muffler & Head.

Thanks
Old 03-21-2012, 12:38 PM
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jaka
 
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Default RE: Thunder Tiger F-91S low speed needle default setting

Hi!
It's simple! You start the engine and let it run slobbering rich! Run a tank or two and then set the low speed needle! Open it some ...not as much as possible but 3-4 turns from fully in. But if you want to open it fully, that's Ok too. Then listen to how the engine sounds when you give full throttle!!!
It should respond to full throttle imidiately without hessitation! If not turn the low speed needle in some! Keep on doing this test with long idleing and full throttle for some minutes and you will get your engine set!-If you hessitate ...get help from a friend !

Keeping 4000 rpm when running is not written in stone! What's important when running in a ringed engine is to not let it work too hard or rew too much!
Old 03-22-2012, 08:28 AM
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Default RE: Thunder Tiger F-91S low speed needle default setting

That is not an early model, I do not believe it would need the choke assembly to run right. To run at 5000 would be at speed with an extremely rich mixture. By at speed I mean not at idle so you do not need the low speed needle to be set right. I would still take out the glow plut and squirt a shot of fuel throught the glow plug hole to prime the engine for the first run.
Old 03-22-2012, 08:45 AM
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carrellh
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Default RE: Thunder Tiger F-91S low speed needle default setting

The current model has the black head and muffler. Prior models were natural finish.

Break in is normally done at wide open throttle and you limit the RPM to 5000 by making the high speed so rich it will not run faster. That keeps it cool and lubricated as the ring and cylinder break in.

I'd make sure the LSN is not completely closed, maybe one or two turns from closed. Then I'd open the HSN needle even more than the manual calls for on initial startup to be sure max RPM is not too high, and adjust from there.

If you're not comfortable with that: Great Planes / Hobbico is now the distributor of Thunder Tiger so you can probably call Hobby Services to get a starting point for the LSN.

http://www.ttamerica.com/techsupport.html
Telephone: 1-217-398-8970. Available Monday-Friday, 8am-5pm U.S. Central Time.


Old 03-23-2012, 03:48 AM
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Default RE: Thunder Tiger F-91S low speed needle default setting

Set the barrel, so you just see a sliver of opening. Put a short piece of fuel line on the inlet barb, then close the lo-spd needle while blowing on the short piece of fuel line. When air passage stops, adjust the needle back out 'til you can just get an airflow. This will put you close. The rest is fine tuning. Good luck, red
Old 09-21-2021, 03:36 PM
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Default

If you disassembled yhe engine, pay attention to the timing in case you took it appart.

HSN
Fully open throttle and close the hi speed needle, put a fuel line on the carburetor nipple and start blowing while opening the HSN until you start getting air through.

LSN
Close the carburetor until you have about 1/8 to 1/16 close the low speed needle and start blowing until you start getting air through.

You now have very close settings. The engine should start.
Old 09-22-2021, 05:55 PM
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Default

Originally Posted by jucava View Post
If you disassembled yhe engine, pay attention to the timing in case you took it appart.

HSN
Fully open throttle and close the hi speed needle, put a fuel line on the carburetor nipple and start blowing while opening the HSN until you start getting air through.

LSN
Close the carburetor until you have about 1/8 to 1/16 close the low speed needle and start blowing until you start getting air through.

You now have very close settings. The engine should start.
This thread is 9 years old. You think the OP is still reading this?

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