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Old Oct 10, 2012, 07:14 PM
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United States, MI, Bloomingdale
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New To Nitro Tuning Problems

A few weeks ago I bought my first nitro plane, an Alpha 40 rtf. I've flown it a few times and have ran into a few issues with the engine. I'm not new to nitro or planes, I've had several nitro cars and a Hobbyzone super cub and Parkzone T28, so I know the basics of flying and nitro engines. I just need your guys opinions.

So far I've flown the Alpha 6 times, the first few flights went great, the engine ran strong and never had an issue. After 4 flights I changed the 3 blade prop to a 2 blade prop and took off the flywheel weight, cause everyone said it made the plane fly better. Ever since then the engine hasn't been running well. The weather has also changed drastically from being warm to cold between switching props affecting the tune.

The engine seems to be running rich, whenever I increase the throttle, the engine is sluggish in acceleration. And if I lean the high speed needle some the engine will cut in and out at full throttle. I haven't been able to find the sweet spot, where it'll accelerate smoothly and not cut out at full throttle.

I'm thinking that probably one of my needles is too lean and one is set to rich or I might have a possible air leak which leads me to my next question.

When I prime the engine by opening the throttle to full and plugging the air intake and flipping the prop, the fuel goes into the carb fine but as soon as I take my finger off the air intake, the fuel starts flowing backwards to where there isn't any fuel in the carb. Is this normal with nitro planes? Or is it an air leak somewhere in the tank or fuel line? With my nitro cars the fuel stays in the carb even after priming the engine.

Thanks to whoever can help, I've been thinking alot about this and still haven't been able to figure it out.
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Old Oct 11, 2012, 09:17 AM
The Prez....... again
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United States, IA, Rockwell
Joined Jul 2011
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You are already too lean, you need to richen the mix more. Cold air needs more fuel. I know it sounds counterproductive. Cold air is more dense so more fuel is needed. You may have to loosen the adjustment to get more range out of the needle valve. I assume it has the stop so you can't over adjust it? Loosen the set screw and then you can turn the needle valve itself.

Oh, wait, I'm thinking of the idle mixture screw. In any case more fuel is needed. Richen it until it blubbers and then lean till it cleans up, then a tad back rich. If you have a tach, set it 500 to 600 rpm to the rich side of top rpm.

Good luck!

Ken
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Old Oct 11, 2012, 09:18 AM
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United States, TX, Leander
Joined Sep 2003
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If the engine still has all those limiters on it, remove them. They are not needed and just get in the way. You just need to fine tune the engine now that it has more run time. We do the prop change like you for most of my students with no problems.
Edwin
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Old Oct 11, 2012, 04:35 PM
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United States, MI, Bloomingdale
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Thanks guys, also is it normal for fuel to flow backwards after taking your finger off the carb intake when priming the engine? If its not, then I might have an air leak somewhere and the problem wouldn't be tuning related.

I'm also going to try a new glow plug, O.S. A3. Its what I have on hand and use them in my cars with great success. I'm still using the original after 6 flights and the bottom of the plug is black and the wire is white.

Hopefully I'll be able to tune the engine tonight and get it in the ball park, the wind is gusty at 30 mph though so no flying.
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Old Oct 11, 2012, 04:47 PM
Hutch
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United States, Mt, Bozeman
Joined Jan 2012
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The trick to priming may not be giong full throttle. About any engine will do this as the fuel is not being stopped from flowing back by the low speed needle. (its in high flow "mode")
I either prime it just about 1/3 throttle, or keep the tx handy and put it to low throttle before your take your finger off the exhaust.

* usually not an air leak, but not a bad idea to check lines, they seem to go bad right at the fitting connection.

I like the low speed needle adjuster on, as I have had variation in temp/pressure affect the low side. It makes it nice and easy with that little lever deal.
Sounds like you are rich on the low side and lean on the high side. Adjust high first.
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Old Oct 11, 2012, 08:23 PM
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Thanks hutchinstuff, very good info and glad to find that its normal.

On another note, after bending the stops back, I found out how many turns my high and low speed needle were set from the factory. My low speed needle was around 1 1/5 turns, and my high speed needle was, guess what, 1 1/4 turns! So much for "no tuning required from the factory" atleast you would think the HSS would be in the ballpark. They also claim that the stop would prevent from leaning the engine out to much. All it prevented me from doing was checking to see if the needles were in the ballpark.

Now I'm worried because I ran the engine when it was first breaking in lean because thats what it was set from the factory. It runs fine now but I'm worried about the long term life of the engine.

After reseting the needles 1 1/3 turns for the LSN and 3 turns for the HSN I ran the engine and got it tuned properly. Now it runs great! I ended up with 1 1/4 turn for LSN and with 2 1/2 turns for the HSN.
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Old Oct 12, 2012, 08:19 AM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
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At this point all you can do is run the engine and see what happens. It's running good now so go fly and don't worry.

The stops are a mixed blessing. For newbs it takes some of the worry out of mis-adjusting. On the other hand, as in your case, it was mis-adjusted from the factory making for a poor running engine. I had the same deal with a club mate. His low speed was so far out of wack it would die anything below 1/3 throttle.

Ken
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Old Oct 15, 2012, 03:19 PM
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Joined May 2011
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Sounds like you got it fixed. If you are concerned about the engine running lean, take the muffler off and have a looksee inside the cylinder. Should be clean without any scoring. The engine is most likely OK,
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Old Oct 16, 2012, 06:56 AM
use the 4s luke, use the 4s...
scrub monkey's Avatar
Australia, QLD, Booyal
Joined Sep 2012
861 Posts
From what im hearing you are trying to tune this like a car engine. no, no, no, no, NO. They are completely different in what you tune them for. I could do a write up on how ro tune it but best bet is go read the sticky in the fuel engine forum up above this one. If you want. Can write up how to do it. With aircraft you aim to tune it for max power, no burbling when quickly throttled up from a LONG (i.e. about 40 sec) idle and to have a slow RELIABLE (i emphasise reliable) idle.
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Old Oct 17, 2012, 10:16 PM
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United States, OR, Portland
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Quote:
Originally Posted by scrub monkey View Post
From what im hearing you are trying to tune this like a car engine. no, no, no, no, NO. They are completely different in what you tune them for. I could do a write up on how ro tune it but best bet is go read the sticky in the fuel engine forum up above this one. If you want. Can write up how to do it. With aircraft you aim to tune it for max power, no burbling when quickly throttled up from a LONG (i.e. about 40 sec) idle and to have a slow RELIABLE (i emphasise reliable) idle.
Just to jump in here, don't you mean tune for max power while still staying slighty rich? Isn't the lean side always more power but harder on the engine?
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Old Oct 17, 2012, 11:28 PM
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Not only is it harder on the engine, it will burn it up completely.
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Old Oct 18, 2012, 05:01 AM
use the 4s luke, use the 4s...
scrub monkey's Avatar
Australia, QLD, Booyal
Joined Sep 2012
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Yeah i should have said turn it back 1/8-1/4 of a turn from when the rpm peak
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Old Oct 23, 2012, 11:06 AM
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i usually only go 1-2 clicks back from high rpm, but I'm looking for max performance. I fly my 2 and 4 strokes on Powermaster 15% and don't use afterrun oil. After 2 years flying nitro 40 size planes, I haven't had any engines burn up. My VQ Zero with Tower .46 Pro engine screams lean in an enclosed cowl and is flying great. I usually run my engines at least 1x per month.
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Old Oct 23, 2012, 02:05 PM
Hutch
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United States, Mt, Bozeman
Joined Jan 2012
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Will nitro engines run well lean of peak? In full scale, combustion temps go down, as does RPM. *I have yet to try this on glow engine.
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Old Oct 23, 2012, 02:07 PM
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Quote:
Originally Posted by hutchinstuff View Post
Will nitro engines run well lean of peak? In full scale, combustion temps go down, as does RPM. *I have yet to try this on glow engine.
if you lean the high speed needle too much, the rpm will drop and usually will cut out.
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