I know there is another thread on this engine; a long one at that and I have read it and followed its recommendations.

My problem isn't the top end or the low end but the mid range. It will run fine at the top end, well at the bottom but when I pick the nose up at half throttle or so it leans out something terrible.

I took the carb apart and the hole was off kilter so I drilled it out as the original thread suggested. When I retuned the engine it behaved the same way.

Fuel is Powermaster 15% sport fuel, prop is a 12.5x3.75 APC and it's mounted on a magic extra 300 (or was until last night at least). My first thought was the tank was too low causing a fuel flow problem so I raised it up and now it's almost even with the carb (just a smidgen lower). Still the same problem. I drilled out the fuel inlet so that there was no longer any blockage - same problem. I hate fiddling with engines - I love engines and feel like I'm very good at tuning them but when I have one I have to "fiddle" with I get real frustrated and prefer to simply give up and spend my time more wisely. I didn't pay for this engine so I really don't care much about it but I did want to give it a shot. My fuel lines in the tank are what came with the ARF and they seemed a little narrow but I just don't think that's it. Regardless I will replace them before I try again.

I really am quite tired of this engine so I'm not sure I will try it again on this plane but I will probably put it on my ugly stick (the run - in plane) and fiddle with it some more.

Any thoughts?

You might share with us what muffler you are running.

Some 47's came with a "tuned" muffler and some had a regular one. Also this the most popular muffler size in existance so it could have various other designs on it?

It's got the shiny longish muffler that I suppose is the tuned muffler.

I had considered trying another muffler....

Experiment with the low speed needle setting. I have seen two examples of GMS .47s that were very poor at drawing fuel (they would sag badly when the nose was lifted) respond dramatically to low speed needle adjustments. In some of the GMS .47 carbs, the low speed needle setting can influence the operation of the carburettor all the way up to full throttle. I know, it sounds implausable... but before you bin the engine, try it out.


Read JDW's posts in that original thread. He discovered this phenomenon.

Most typical the tuned muffler has a rich mid range.

But the turned muffler has very low internal pressure and allows fuel draw problems.

They produce very good power on the top end when set correctly though.

The GMS .47 is delivered with one of two muffler types:

1) A finned, two piece unit that looks like a stock OS style muffler.

2) A three piece "Tower style" muffler with a shiny centre section.

The engine, properly set up, will run well on either muffler and will yield about 300-500 rpm more on the Tower style muffler.

Any engine that does not conform to normal operation is not an engine that stays in my stable.



Difficult engines on sport planes simply aren't worth the trouble (competition is entirely different though).

So, with regards to your comments about the low end needle. My helper and I spent the better part of 2 tanks of fuel slowly leaning the low end mixture to get proper transition (using the pinch test a lot to ensure we did not go too lean of course) and when we had a good transition if the nose was up the midrange would sag horribly.

Being that it's on a 3D plane I need my mid range to be rock solid. So, like I said on this plane I'm putting a different engine that I know is good. I will probably continue to fiddle with it on the ugly stick though.

I'll try another muffler as I have a few extras.

The Macs "One piece" for the OS 46 work pretty good on this engine from a fuel draw point of view but the top end suffers somewhat.

The Macs has a lot of pressure as it comes from Macs.

The GMS .47 seems to be an engine that suffers from a fairly wide manufacturing tolerance. I have worked with about 8 of these engines for guys and they have varied from being perfect out of the box without needing any low end adjustment down to being virtually untunable, depending on the example.

I have seen as much as 1000 rpm difference between two engines, running the same muffler, the same prop, on the same day with the same fuel.

It just seems to be the luck of the draw with the .47s, more than any other engine I've seen.

submikester....

....I think I can simplify this for you....

....any time our aero-model engines "lean out" when the nose is raised, it
is caused by one thing....and one thing only.....lack of fuel pressure. It doesn't
really matter if it is suffering from lack of fuel on the low end (idle mixture), or
the top end (high speed needle)....if the engine is leaning out, it is from lack of
fuel. This reality is simple.

Keep in mind, there are only two "adjustments" on the GMS .47....the low and
high speed needle adjustments....there is no "mid range" adjustments. We all
know that the low speed needle adjustment, and the high speed adjustment

effect the mid range....but, even if the low speed is set slightly rich (the
way I like it) and the high speed is set richened for flight....when you get to the
mid-range....in a "stand alone mode"....the mid range is kind of "on it's own".

You cannot richen the low speed enough, or the high speed, because you will
be outside the parameters on both ends, meaning....if the fuel pressure is not
enough....you will not be able to compensate by over richening either end of
the spectrum....rather, performance will suffer to the extent that the mid-
range won't really matter.

When you go out of the low needle spectrum, and are advancing into the high
speed needles influence....there is only one thing that is controlling that portion
of the mixture, and that is the taper of the needle, working in conjunction
with the design of the nozzle.

Another thing to keep in mind is....the low speed needle adjustment isn't really
a "fuel circuit"....it is simply a method of "blocking off" the fuel mixture provided
by the needle/nozzle combination from the high speed needle. This of course
relies on the principle that the needle/nozzle relation is perfect at all settings,
and it also assumes that the fuel pressure is constant, or at least satisfactory.

This is of course, may not the case.

This is the main reason the YS engines are so succesful. By utilizing their super
high pressure fuel systems (enough to blow some fuel tanks in half) the engine
will not "lean out" in any case. The fuel pressure is more than adequate
to eliminate the leaning-out problems associated with the rest of the aero-model
engines (non pumped) no matter what the throttle setting, no matter where the
tank is mounted, no matter how much fuel is in the tank....or no matter what
attitude (position) the airplane is in.

The bottom line is....fuel pressure is not that great at half throttle...less than at
full throttle, to be sure. Were you planning on going verticle at half throttle ? If
the engine is leaning out on the ground at half throttle, you must address this
problem.

When I started looking at my engine for possible problems, I noticed that the
nipple on the muffler had flasihng in it....it wasn't drilled properly, and probably
wouldn't have delivered full pressure to the tank. That was the first thing I did
....was remove the restriction from the exhaust nipple....

....check yours. If you aren't getting proper pressure to the tank, all bets are off.

FBD.

Dave, those are exactly the conclusions I came to. I've just never experienced a problem with an engine such as this. So, I'll go into the garage and give it another once over and prepare for fiddling with it on my Ugly stick.

Mike....I know you are knowledegable....

....is the engine mounted side-ways ?

....yo, Mike....one thing you might try is sealing that muffler and pipe flange
real good. If you are leaking pressure out of the seams ....you will not have
proper fuel pressure in the tank....and that will (or could) cause a host of
lean fuel and problematic conditions.

I just thought of this possible problem. I have been running the Tower .75
engines since they first came out....thet are just like your muffler....

....they leaked like a sieve from every seam. This could cause a loss of
pressure to the tank. I had forgotten about it....but, I now seal all these type
mufflers out of habit.

Now, I'm wondering if these pressure leaks in the muffler....coupled with
some of the other minor problems....could manifest themselves into a bigger
problem....one like you are experiencing ???

FBD. [sm=72_72.gif]

It was and will be mounted upright. I hadn't sealed anything up on it. The flange to muffler seal seemed pretty solid though (never know really however). I haven't done an actual leak test though.

For the sake of curiousity I will continue with it (since I started this I might as well finish it). I think the first thing I will do once I have it on the ugly stick is run it as it was and see if the same problems exist being that on a different plane the tank will be different and all that. If it still exhibits the same issues then I will try a standard OS muffler (assuming they fit of course) from a .46 that I have. See if that improves things, since we are both taking things for what they are. A lean condition when the nose is held high at the mid throttle range.

Oh, and yes - I am planning on going vertical at 50% throttle. A properly setup 3D plane should hover at about that setting (not that I have any properly setup 3D machines - but that's what I've read).

....Mike....I have a habit of giving full throttle when I go vertical....

....but that's just me.

BTW....when your engine is leaning out....leaning out the low end further
won't help....trust me....I'm a "carb man" from way back.

Turning the low speed screw "in" does nothing but restrict the mixture
from the already pre-adjusted mixture of the main needle/nozzle. The
low speed needle doesn't really adjust the mixture, there is no low speed
"circuit".

FBD.

Dave, we can argue finer tuning techniques if you like. If it gets heated enough we can even meet somewhere's around covina or so to duke it out (that's about half way between us I'd say).

In my experience to get a proper transition from low throttle to high throttle both the top end and the bottom end should be "optimized" to the proper setting (or whatever term you prefer). I've got a fair amount of carb experience myself but I'm no expert, I just know my way around a bit. So when I start tuning an engine I first set the high end mixture to where I want it (on a new engine of course I back it off a few rpm from its highest) then I start working on the idle. I like an engine that idles well to I always try to get it the best I can. When I do that I use the pinch test, most of my engines are 4strokes however and they are much easier to tune for me. So, when I say leaning out the low end I mean to say I'm trying to adjust the idle to the proper setting. Mainly I find that once I get the setting on both the top and bottom end the way I want - the mid range is if not close enough to perfect not to fuss with or close enough to where getting it right isn't a fuss.

Here are some pictures, one is of the GMS 47, which says 47 II on one side and the other is of my trusty dusty OS 46 SF ringed engine that I have mounted in place on the airplane I desparately have wanted to fly the last three weekends.

That particular OS 46 SF ringed is actually a couple of different engines I pieced together from some crashed engines. One was a ringed heli engine and that thing purrs like a kitten and with 20/20 is sings. Mostly it's been on trainers that I use for instruction (and for knocking around the ugly stick) but I figured it was time to give it a shot on something that could use such a nice running engine. We'll see how it does...

Also, I checked the nipple on the muffler and it seems pretty clear.

--------------


I adjust my engines to run their best with the nose of the model pointed vertically and then live with the consequences with the nose lowered to level.

Additionally, you may have to put an ounce or two of fuel in your fuel tank to make this vertical adjustment, plus you still need to leave it a tad rich, just to be safe.

Fifteen percent nitro is pushing it on a brand new Chinese two-stroke. Five to ten percent nitro would be better, unless you shim the cylinder head to reduce the compression ratio. I would run this engine on a 10x6 prop until it has some running time accumulated. It will lessen the effect of being overcompressed for the amount of compression and a 10x6 is not small enough to "over rev", as some people like to say, your engine. It loves to spin up there really high.

As the engine gains running time, it will become less sensitive to mixture settings and will require a bit of leaning to keep it running the same. This is good. It means that the engine is bedding in just right.

Yo, Mike....this :

...was a reference to another post, on the other thread. A guy discovered that
when he adjusted his carb properly....in his case, leaning out the low end, the
engine ran alot better. This was described as a new phenomenon. [sm=72_72.gif]

....good one, Mike........you would have had to caught up to me about 30
years ago for "some dukes ".... (LOL)

...back to your engine....you'll always have some leaning out problems with
an upright mounted engine to some degree.....key words "some degree".
You can get away with it sometimes....sometimes not, it depends on a lot
of things, as you know. There is no getting around the fact that when the
nose is raised...the carb gets way higher than the fuel level....the only thing
that can save you then is fuel pressure, like in the case of the YS engine I
used as an example earlier.

Why does one engine work, when another is problematic....same plane, same
tank, same fuel lines ???

Some small things that cannot be seen, and are not really detectable without
real careful scrutiny. Things like....a slightly blocked muffler nipple, a tiny air
leak at the carb mount....a tiny air leak at the front bearing....a less than
perfect seal at the head gasket, due to an improperly torqued head....that
only manifests a tiny leak when the engine gets real hot.

A couple of these small things can add up to a problem, especially with an
upright mounted engine that is leaning out any time a positive "G"
force is applied to the tank. Add to this....the small quirks and differences
between engines....and "their" specific preferences to plugs, fuel and props....
not even bring in vibration....and the problems that come in to play. These
are reasons why one engine would be happy in a certain instance, when
another....seemingly "good engine" runs like poopy in the same plane.

I know you know this stuff, Mike....I'm preaching to the choir.

Mike....are you coming out to Jack Rabbit Dry Lake this weekend for the
"Revvers Meet" ???

FBD.

My hope is that by putting the engine in a "known good" plumbing setup I can make sure that isn't the issue. By also testing the fuel plumbing in the Extra with a known good engine, if it behaves the same way I may just have to end it all.

What is this "revvers meet" you speak of?

The "Revvers" are the Speed Freaks from all over the Universe....

....we have club. The second meet of this year is this weekend. A bunch
of the guys from Calif. will be there, as well as out of state....

Rabbit Dry lake is out near Victorville....between Apple Valley and Lucerne
on Hwy. 18.

http://www.rcuniverse.com/forum/m_4670218/tm.htm

I'm not really into the whole "speed" thing but thanks for the invite. I do have a Kougar on the building board though (with retracts - which was a crazy idea).

You can come anyway....bring a plane....it's just for fun. Come out for the
day, or camp out Sat. night. We will have a blast.

Wrong answer. He discovered that adjusting the low speed needle setting could affect where the main needle had to be by up to 3-4 turns and could greatly influence fuel draw. This was the phenomenon he discovered.

Here is the post:

http://www.rcuniverse.com/forum/fb.asp?m=3516782

Have you read it Dave?

Submikester, depending on where your carb is in the "sum of tolerances" continuum, this phenomenon may or may not apply to your situation.

Sounds to me like someone was trying to set the low end before the high end was adjusted properly.