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3W 100 / Tillotson carb adjustment - midrange

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Old 10-25-2002, 09:56 PM
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DMcQuinn
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Default 3W 100 / Tillotson carb adjustment - midrange

Here's the symptom: Engine runs fine at idle and at full throttle and in fact generally transitions well. However, after extended running at a very fast idle (1/4 throttle), quits (or sags) when the throttle is advanced. I richened the low end and it seems to be better (one test flight). However, it is clearly on the rich side at idle. I can pinch the fuel line shut at idle and it runs for 5 seconds and then speeds up quite a bit before finally slowing or quitting.
I have read all the threads about carburetor mixture settings. Generally they say to lean the low end until it does not transition well. then open it back up a little. And lean the high end at WOT for max rpm and then richen a little. When I do this, I can get a very reliable idle and good transition on the ground, but I think it is going a little lean at fast idle / quarter throttle.
I have been practicing my harrier (very high up) and this is when I have the problem. The plane harriers at about 1/4 throttle and after 10 or 20 seconds of this, when I open it up, it quits (or sags and nearly quits).
26x10 wood prop, amsoil 100:1 oil,.
At 1/4 throttle, I assume both needles are contributing to the mixture.
The HS needle is now 1 turn open and the low speed needle is now 1.5 turns open. This turns out to also be the recommended setting in the manual from 3W.
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Old 10-26-2002, 01:25 PM
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Default 3W 100 / Tillotson carb adjustment - midrange

If it's sagging at 1/4 throttle, then the low end needle needs to be opened slightly. The high end needle does not affect the mixture until about 1/2 throttle. It could also be overheating in the air when hovering causing it to sag. The carbon fibre intake horn that 3W sells greatly improves the throttle response of my 3W-100. Best $40 I've spent. You may also find that running a richer oil ratio will cause the motor to run cooler. Some have reported that the motors run 30F hotter on the 100:1 oil. Amsoil also makes a 50:1 type synthetic oil.
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Old 10-26-2002, 02:09 PM
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Default 3W 100 / Tillotson carb adjustment - midrange

I agree with Diablo, to lean on the bottom end. I only ran mine on Aimsoil 50 to 1 racing 2000.
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Old 10-26-2002, 08:24 PM
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Default Carbon Fiber Intake Horn?

what is this? Is this to replace the phenolic separator that goes between the carb and the intake manifold? Or is this like a stack that goes before the carburetor?
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Old 10-26-2002, 08:36 PM
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Default 3W 100 / Tillotson carb adjustment - midrange

He is talking about the 90 degree stack.
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Old 10-27-2002, 12:21 AM
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Default 3W 100 / Tillotson carb adjustment - midrange

Intake horn looks like this:
http://www.aircraft-intl.com/catalog...f_manifold.jpg

Yes, I tried the diaphragm tube to the fuse method. Well over 100 flights that way, could not get the mixture correct in the midrange, lots of burbling inverted and on knife edge, also tended to load up at idle sitting on the ground. Switched to the intake horn....now perfect...well over a 100 flights that way. Also the horn makes the engine run a whole lot smoother at part throttle.
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Old 10-27-2002, 03:53 AM
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Default Why the tube to the intake?

Thanks for the reference to the picture of the CF intake. Why do they show a tube to this? I think this must be the tube from the reference side of the diaphragm? I have mine running into the fuselage.
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Old 10-27-2002, 05:42 AM
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Default There are several ways

To remedy the midrange maladies of the gassers. You've seen the horn and are asking about the tube in the venturi scenario. Here is a picture of one... Basically it's kind of like trying all of the possible solutions and seeing which one works for you. I've tried the in fuse version that you mention and it didn't work in a particular plane as well as the venturi method for instance. Keep on trying_bob
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Old 10-30-2002, 04:18 AM
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Default Can I just make a 90 degree intake?

I got an email from gerhard at aircraft international saying the CF 90 degree intake horns are backordered three or four weeks. Is this device any more complex than a 90 degree fitting. couldn't I just find a flange that will fit onto the carburetor and solder a 90 degree elbow onto it?
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Old 10-30-2002, 12:32 PM
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Default Carbon fiber intake

Call Bobby at Cactus Aviation, he has them in stock. I just bought one 2 weeks ago. His Phone # is (520)721-0087. He is a 3W dealer also.
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Old 11-04-2002, 01:32 AM
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Default 3W 100 / Tillotson carb adjustment - midrange

Your engine quitting while hovering is most likely an overheating issue. I had the same problem. I did not have any cowl baffles installed on my Cap to keep the engine cool. The engine would run great while flying around but after 15-20 seconds of harrier, or hovering, the engine would quit. I installed baffles and have not had a problem since. Cactus Aviation has good instructions and pictures on how to install baffles.
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Old 11-04-2002, 04:28 AM
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Default I have air baffles...

I have installed air baffles inside my cowl, but they are not perfect. This was my first attempt. Perhaps I should re-do them. I have a good baffle connected to the lower portion of the cowl, but air can pass over the top of the fins without actually going through the fins. Thanks for the advice. After a normal flight, I have licked my fingers and touched them to the fins just after engine shut-down. There will be a sizzle indicating the temperature over 212 degrees. (I do not have a temperature gauge).
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