cruzomatic

My Feedback: (17)

I'm just about ready to give my 4*60, TT.91FS its maiden. I have a question though,,,,in regards to the low speed needle. When I give it full throttle it dies. What's causing this,,,too rich or too lean? I need to adjust which needle, the high, low or both?

thanks,,

w8ye

My Feedback: (16)

Try it richer on the low speed. Just move it about an eigth turn at a time.

The lean condition is usually where it just suddenly quits when you give it the gas. Sometimes, you may hear a backfire?

Too rich and generally it spuuters and carries on. Sometimes it recovers and sometimes the glow plug will get cooled off by all the extra fuel and it will stop after a fashion.

Good luck

Jim

David Cutler

The low speed needle is too lean.

-DC

DarZeelon

Hi Adrian,

Did you try to open the throttle slowly?

Try it. If at a certain point it quits, your high speed needle is too closed, or you have some other kind of obstruction, disturbing fuel flow to the engine. The engine is getting insufficient fuel for high speed operation.

If it goes to high speed, stays there and can be richened to slower speeds, the mal-adjustment is in the idle circuit.

It could either be too rich, or too lean. But from you description it sounds like it is lean. Try to richen by 1/8 of a turn, at a time.

If you have richened it several times with no improvement in response, try leaning.

Sincerely,

cruzomatic

My Feedback: (17)

Thanks guys,,, I'll give the low speed an 1/8th of a turn out and the high speed a turn out as well,,

hey Dar,,,,good to hear from ya again,,,,I'm almost in the air. I'll post pics soon,,

Ernie Misner

Dar is absolutely right on. In the long run though you will need to develope an ear for tuning and understand why things happen. If too rich on the bottom end the plug will be fouled with a sudden throttle opening. If too lean.... it will die from the just the opposite, not enough fuel for the sudden supply of oxygen that will gust in.

Pinch the fuel line shut for a while when it is idling. If the rpm's increase quite a bit, it is definitely too rich on the bottom end.

Ernie

cruzomatic

My Feedback: (17)

Well, I opened up the low end needle some and that seemed to help out a little, but now have another problem. Just as soon as I would remove the glow plug igniter it would die??? What would that mean? The transition from low to high was good though??!!

Wasn't able to give it it's maiden today.

Guest

[Deleted by Admins]

ajvpb

My Feedback: (3)

Get the new plug, and then if it happens, you opened it up to much. In some engines it is very exact, others can be in the ballpark. Some may need the smallest incriment of a turn to get it right. For me, the right setting seems to be after I remove the glow starter, you can hear a small drop, but it does not load up, bog down or hesitate on throttle up.

Spaceclam

way too lean. if it is just a bit lean, it coughs but keeps on going

cruzomatic

My Feedback: (17)

The plug is OS Type F and it's brand new. Probably has about 30 minutes or 1/2 gallon through it, if that much. Actually, I took it out and it looked ok,,,but then again, don't really know what I'm looking for. It looked as a brand new one does.

Too lean huh?? According to the manual it says 'open up 1/8th at a time.' Is that about right?

cruzomatic

My Feedback: (17)

Also, what would be a good starting point for the low end? The manual recommends a starting point of 2.5 to 3.5 turns out on the high end, but has no mention for the low?

Spaceclam

but depending on the heat, fuel, oil content, nitro, and so on, you may have to give or take. assuming your valve timing is right, and you do have compression, there are three things that make an engine run: air, fuel, and spark (glow) if you are getting air, and you know your glow plug is operating PROPERLY (type f glow plugs are exceptional, they last forever and operate very well) than the only thing left to abruptly stop an engine from running is fuel, or lack thereof. when you spool up an engine and it dies abruptly, (considering that everything else is correct mentioned above) there is no fuel. that would be the low end, if it happens on spool up. try giving it throttle slowly. if it happens within about 80-100% of it's maximum throttle, your needle may be too lean. other than that, is is most likely low end. if you don;t believe me, you could try anyway. it won't break your engine, and therre is a chance that actually i am correct, and it may even help you

cruzomatic

My Feedback: (17)

Spaceclam, thanks for responding. I believe ya,,,,I'll give it a try tomorrow after work. I'll back out the low end some more.

I did give if full throttle slowly and that worked well. It was only when we removed the igniter it would die while increasing the throttle.

Spaceclam

did it sputter or die abruptly? now that you tell me about the igniter, it is sounding more like a weak glow plug. here's my thinking:

works with igniter, doesn't without. that means something with extinguishing the glow plug, or it not working, because that is all the igniter affects

sometimes when you spool up your engine the massive amounts of incoming fuel will extinguish the plug. type f plugs are really hot running plugs, that shouldn't happen

works when you do it slowly, not when you gunn it

theck the glow plug before anything. also, you can take out the plug, and see what was happening. look at the bottom of the plug. if it is fairly clean, maybe a little tanned, everything is running normal, probably the plug is at fault. if the coil is white looking, not silver, it was running too lean altogether. if the plug coil is stained black, and doesn't lite up well, it is probably running too rich. it is also possible that your plug is also just old and worn

cruzomatic

My Feedback: (17)

It would sputter right around 1/4(+) throttle on the way up. It did run a bit without the igniter attached but only at high RPM. Lemme take the plug out and take a pic of it and post it,,,? Give me a few minutes,,,,,hang around if you're able.

Spaceclam

thanks. i can wait, but does it sputter and die or just stop running?

cruzomatic

My Feedback: (17)

here's one,,,,thanks for holding,,,,I think I may have a better one? Give me a second.

cruzomatic

My Feedback: (17)

here's another,,,sorry about the quality,,,my digi cam is kind of a dinosaur.

cruzomatic

My Feedback: (17)

It sputters and dies.

Spaceclam

the picture is kinda blurry, and i can't even see the filament. don't bother with the pics, just use what i posted and make a decision, because with the file size limit, i will never be able to make a good decision. but, that doesn't really show what goes on during spool up, i was just throwing that out there as kinda related information. if it sputters and dies, it is most likely really rich. engines can run really rich at high rpm's but load up at lower ones. too muh fuel=extinguished glow plug. throttle it up slowly it is fine, but gun it=flood it all adds up. i think i can go against what i had before, because from your description i thought it just quit abruptly. it is most likely way too rich.try closing your low end about a quarter turn. that is a lot, but jsut try it. if it gets better, lean it out a bit more, in small increments. if it gets worse, i am retarded, and keep richening it out. but now it sounds rich to me

cruzomatic

My Feedback: (17)

I understand, yeah, the pics aren't good. What is a good starting point for the low needle? I'm assuming all the way in (lean) would not be a good one. Perhaps a couple of turns out?

David Cutler

Approximate process to tune an engine:-

1/ Open both the high speed and idle needles more than you think necessary. That is, both should start rich.

2/ Open throttle fully, and, when at maximum throttle, slowly screw in the high speed needle until the revs build up, then start to slow down. Open 1/4 to 1/2 turn, depending on how well run-in the engine is.

3/ Close throttle to the slowest possible sustained speed then suddenly open to full throttle again.
- If the engine stops, open the idle needle 1/4 turn
- If the engine splutters but does not stop. close the idle needle 1/4 turn.

4/ Continue 3/ above until the engine cleanly and quickly speeds up to full throttle. As you get close to the ideal idle needle setting, move it only 1/8 turn each time.

5/ Check the high speed setting again.

That should be enough to get the engine running right enough to fly.

-David C.

Sport_Pilot

The TT 91 has a habit of fouling plugs during break in. I use a cheaper Fox Miricle plug for break in because of this. Then switch to an OS F for the maiden flight and till I feel comfortable with leaning it out. After that I use different plugs depending on which fuel I am using. I think using a new plug would do the trick.

DarZeelon

Adrian,

The fact that your plug is almost new, does not prove beyond reasonable doubt that it is OK. It can be defective.

Try to borrow a four-stroke plug from a flying buddy, one that has been running in his engine and is known to be good.
If your trouble continues, it is your adjustments, or maybe you still need some break-in time.

If the problem is gone, you've found the culprit.

Sincerely,