Need some engine tuning help. Broke engine in as per instructions. No problems.

But when I try to tune it for operation, the engine cuts out when throttle is ramped up, or when throttle nears idle on ramp down. It'll putter out.

What's causing this? Any suggestions?<br type="_moz" />

You didn't say which engine but I'll assume it is a Thunder Tiger Pro46? The low speed mixture screw in the middle of the throttle lever is in too far

yes, the idle needle valve is too lean. It's inside the throttle barrel.

TT Pro 46<div>
</div><div>I'm not sure what's happening and how backing it up will help. Please explain.  Thanks in advance.</div>

The idle mixture is too lean.They told you how to richen it up some

Thanks, I'll give it a go.

Hey Windgap, they say a picture is worth a thousand words:



That screw head inside of the round part of the throttle arm on the left side of the picture is the low speed needle adjustment. Just turn that a little bit counter clockwise (lefty loosey for folks with digital watches) to richen your low speed idle setting. Move it gently, about an eighth of a turn at a time, until the engine idles smoothly and transitions cleanly. If it starts to "burble" and hesitate going from idle to high speed, you went too far.

Biged, do you adjust your carbs with a sledgehammer?


Terry

I think those pictures are saying a few more words than what Ed put them up there for?

lol, I just Googled "Thunder Tiger Pro .46 low speed needle" and selected "images" and this page popped up:

http://www.hooked-on-rc-airplanes.co...ning-tips.html

You can rest assured that my engines look far worse!

Here is the engine on my trainer:

G'day

I particularly liked the drawing on Hooked-on-RC which showed the position of the "low speed needle" on the LA as they don't have one. This is going to confuse some poor person. Pity who ever did the page did not use an engine that actually has a LSN as opposed to an Air Bleed which is clearly there but ignored.

It is a pity as most of the info seems sensible.

Thanks for pointing that out Mike. I will try to get that cleared up as soon as I get a chance!

BTW, ALL my engines don't look like that one . That one came from my grave yard of engines that have been buried a few times and was already taken apart, lol

Backed the idle valve as per your suggestions, but no love.  Backed out in small increments althewhile fiddling w/the high speed needle valve.  <div>
</div><div>Am able to blip the throttle w/o any problems now.  Had to lean the high speed valve to get better note.  But on throttle down, the  engine just cuts abruptly.  Also, am not able to idle it to a low grunt.  Just a whiny somewhat fast whirl.</div><div>
</div><div>I've spent hours fiddling, and no flying.  Doh!  </div><div>
</div><div>Am listening, testing, but that dreaded abrupt cut get me everytime.  This bird just won't sing.</div>

Will it idle with the glow driver attached? If so then its time for a new glow plug

It idles fine with/without glow plug, but a bit fast.  Not too fast to be of concern.  The engine is new and so is the glow plug.  It throttles up and runs find until I throttle down.

You might have identified part of your problem. As long as the engine is running and will take throttle, set the high speed, then set the low speed. And it would help to have a tach to be sure you are setting the high speed correctly.

Have you checked the fuel line/fuel nipple to see if they are completely clean. You might have a small piece of debris in the fuel delivery system. It will let sufficient fuel in to maintain idle, and pulls enough vacuum at full throttle to suck in all the fuel needed to run, but in mid-throttle range there's just enough obstruction to not deliver sufficient fuel.

Hi!
Sound more as if the low speed needle is set too rich!!! Turn it in and see what happens.

Hope you use 5-10% nitro and 16-20% oil in your fuel and use a Enya 3 or OS 8 glow plug (sport plugs that throttle good but does not produce best rpm)

Think I found the culprit.  There's air bubbles in the fuel line from tank to carb.  When I'm on full throttle, it's sucking enough fuel.  But, when it throttles down, it seems there's enough bubble to cut the engine.  At least this is what I believe. 

Can this be right?  How do I bleed/rid of em air bubbles?  Where do they come from? 

those silly things can come from several places, basicaly your sucking air into your fuel system somewhere, can be a pin hole in one of the hoses, air leaking around the tank stopper, a hole in one of the tubes, easiest way to fine where your leaking air is to remove the tank from the plane, plug one of the hoses off, place the tank underwater and blow in the oher hose, should see bubbles coming out of the area thats leaking

I'm having a hard time priming. It seems, after I prime it, air backs in from the carb and sits at the top of the tube. When I throttle up, most of them come out, but a few linger. When it comes back to idle, these could starve the engine momentarily.

I think this is what it is. Now the air may not be the problem at all.

(BTW, I tried jaka's suggestion, but it ran lean and the temp of the engine skyrocketed. I won't do that anymore.)

After you prime a glow engine (by putting your finger over the carburetor and rotating the prop a few times), the fuel is drawn through all of the tubing and a few drops of fuel should get into the crankcase of the engine. If you watch what happens next, the fuel in the tubing might flow back into the tank and be replaced by air. This is completely normal and will not affect the normal starting and running of the engine. The main thing is that you got some fuel inside the engine. This will allow the engine to run long enough to begin drawing fuel from the tank on its own. It will very quickly pull the air thru the tubing.

Once the engine is running, especially at full throttle, if you see a bunch of air bubbles flowing through the line then that is not good. You will never get a decent needle valve setting if there is a stream of air bubbles in the line.
One of the more common air leaks is inside the tank, on the line between the stopper and the clunk.

I've found that with my TT Pro 46 engines, the needle valve housing has a tendency to loosen up and create an air leak. Double check that yours is tightly screwed in (don't strip it, just verify). The housing is the part that the high speed needle screws into. it also sandwiches the fuel nipple fitting against the carb.

I had that happen, also. Course smacking the ground repeatedely engine first didn't help. [:'(] I replaced it with a Perry Carbureator and, once I had it adjusted, never looked back. I did have to tap a bolt hole in the engine casting as the plastic carb wouldn't stay put with the dowel-with-a-bite-out-of-it retainer system.

Hi!
There should be no air bubbles in the fuel lines in a correct set up fuel system! Investigate if there is a hole in the tank or in the fuel lines.
Do not! I repeat! Do not accept any air bubbles in the fuel lines!!!
Best tank to use, safest , with best fuel cap security of any available tanks is the Tettra tanks! The rubber expander that all of the other manufacturers use is no good in the long run! It will sooner or later leak.