corsair44

My Feedback: (4)

it is brand new...did the whole by the book break in....it is on a avistar 40....as i was learning i flew it alot at 1/2 throttle on a 10X4 prop. (all i had available at the time) now i am wondering if that has made it so it wont go to full throttle. when i do go to full it just seems to run poor and have low power. cut it to 1/2 and it runs fine. i have tried all kinds of props 10X6 10X8 11X4 now i am on a 11X7.

what prop should i be using for optimal performance?

it idles great as well....if it was overheated wouldnt it run bad at all settings? what are the signs of overheating?

thanks in advance for the help!

w8ye

My Feedback: (16)

Screw your Idle mixture screw out about a full turn and go through all your mixture set up again.

Old fuel can cause this sysmptom too.

If the idle mixture is too lean and the high speed is richened somewhat to compensate, The engine will not run at high speed without going lean and quiting even though you screw the high needle out more.

enjoy

Jim

corsair44

My Feedback: (4)

ahhhh thank you so much! that makes sense...the idle seems to be rich....so if i screw the idle mix out, that will actually lean it out on the idle...which should make things track better on the top end correct? i was really afraid i had burned the engine, even though i am very careful to always run it rich on the top.

ok, i think what i have is the idle is too rich, so i lean the top end to compensate, and then the top end is always rich...does that make sense?

w8ye

My Feedback: (16)

I got lost in your analogy.

The idle and High speed are somewhat codependent on each other. If one is too lean or rich, it will make the other impossible to adjust correctly. To screw the idle out will make it richer but will also make your high speed mixture needle more responsive. Then if you set your high speed at full throttle to the correct mixture, Your idle will hopefully be rich. If the idle is screwed in to far, it restricts the over all floow of fuel to the engine regardless of the more open settings of the high speed needle. Then lets go about getting you idle set.

Start with the idle in a known rich position. Peak the high speed. Then come back to the idle and turn it in 1/8th turn and check your transition. Continue this while periodically checking the high speed for peak. When you get to the point whereby the engine will not accelerate from A idle of maybe 10 seconds, you will need to richen your idle back up to where it will transition to high speed smoothly.

The end result will be that the idle remains a little rich of peak rpm. You can confirm this with the pinch test.

Before you fly, you will need to richen the high speed 2 or 300 rpm because the engine will unload and go a little leaner while in flight.

The pinch test is where you momentarily pinch the fuel line at idle or high speed and note a resulting increase in rpm (was too rich) or an immediate attempt to quit or slow down (too lean) . This happens usually within 5 seconds.

A engine with the idle set at peak rpm will not accelerate. It will just immediately quit when you jab the throttle. A engine that is loaded up with fuel will stumble and sputter before it accelerates.

You will not be able to achieve perfection in all cases (usually the midrange) but compromise the best you can and see what you get?

If I remember correctly, your carb has a low speed mixture pin that sticks inside the high speed mixture fuel tube. Most engines will run pretty good with this low speed mixture needle pin just a little outside the tube when the throttle is wide open. This may be a good position for you to begin with? If your idle mixture pin is up inside the high speed mixture tube with the throttle wide open, it will restrict the high speed mixture flow. The high speed needle will seem unresponsive and if severe enough, the engine will not run at more than mid speed because it gets too lean no matter what you do with the high speed needle.

Enjoy,

Jim

DarZeelon

Cosair,


The generically written (still) OS manual is not necessarily the book that you should go by.

Please read [link=http://www.rcuniverse.com/forum/m_1850473/anchors_1850473/mpage_1/key_tapered%252Dbore%252Cbreak%252Din/anchor/tm.htm#1850473]this RCU thread[/link], to do it correctly next time. Or maybe, you should repeat it the right way.

I don't think any substantial damage was caused to your engine, but running-in a tapered-bore engine, alternating between two-stroke and four-stroke rich, is definitely not the right way to do it.
It is even contradicted by the OS Q&A and by Bill Baxter, who runs the OS support forum in RCU.


Make sure your fuel system is completely clean. Do it by disassembling the needle housing and the carburettor.

Back-flush the carburettor by blowing in through the jet and out through the carburettor's fuel nipple.
Remove the carburettor barrel, after backing out the idle stop screw, to provide access and use a length of silicone fuel line, to blow directly into the fuel jet in the middle. Using a syringe with methanol, will do a better cleaning job.

Do the same with the needle housing.
Back-flushing is necessary, since lodged dirt cannot be forced out in the same direction it entered the lodge.


Use a 10x7, 10x8, or an 11x6 prop.
The 10x4 is for a .25 engine and will over-speed your engine into very inefficient RPM levels.

Open both needles to 2-2.5 turns, close throttle to 1/4 and start the engine.
Advance gradually to full throttle and gradually close the MAIN needle to maximum RPM.
Back it off a bit.

You should be seeing 12,500-14,000 RPM, depending on the prop and the fuel (up to 15% nitro, with Castor oil).
If these numbers are not reachable, something is wrong with the engine!

Rectify the problem, before going any further.


If you do see the expected RPM levels, close the throttle to about 2 mm open and listen.
If RPM continues to taper off, it is too rich.

Close the idle needle a 1/8 turn at a time and gradually open the throttle to full.
Close again to 2 mm... Repeat until the idle speed is steady, or tapers slightly and returns to the same value.

Now, check the transition.

Open the throttle to full gradually and close to idle.

Allow it to idle for 30 seconds and open it rapidly to full.

If it goes to full at once; great! You're done.


If it blubbers and spits fuel on the way up, or just dies after blubbering, it is still too rich.
Lean it a little more (1/16 turn) and repeat the test.

If it hesitates on the way up, or hesitates and then dies, it is too lean.
Do the opposite and retest, until you get it right.


Good luck!

p.s. Did you misspell your pen-name? There is another 'R' in Corsair...

corsair44

My Feedback: (4)

thank you both SO much for the help!

to clarify, based on what you are saying my idle is rich...when i advance the throttle the motor smokes and coughs and then takes off. but when i set the high speed the needle seems unresponsive...i can get it to go rich and 4 cycle if i really crank on it, but when i try to lean it out it just does not rap up...i keep leaning and finally it starts to slow down on the other "side" of the adjustment as it runs low on fuel....hmmmm but it does not stop which must be because it is so rich on the idle that it cant.

does that make sense?


do either of you know the optimum prop for this engine and plane combination ?

thanks again for all the help! really appreciate it!