mscic-RCU

My Feedback: (6)

one note of interest: A lot of guys in the club have experienced problems with the Chinese tanks in the H9 ARF's. I personally have had three split in the neck of the tank. If you are having problems like 2dawgs28 had, check or just replace the tank.

NM2K

My Feedback: (14)

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I'm surprised these fellows haven't discovered electric motors yet. Oh, but you have to charge the batteries, don't you? Bummer. <G>

opjose

Wow yes!

I just went through this with a couple of TH .46 engines (GMS clones).

I simply could not get the engine tuned until I bench tested it and did as you did.

The engines need their low end set almost perfectly before you can tackle the high end, and in turn get reliable idle, etc.

NM2K

My Feedback: (14)

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The proper needle settings are simply set to where the engine runs best. There are "no proper needle settings" in the sense of a number of turns.

All engines are slightly different, as are your fuel, glow plug, prop size, etc. Forget about "proper needle settings" as a finite, specific number of turns and you will be way ahead in the game of running glow engines.

davidsai

hi there can you help me , what is the sparay bar on carb, i haveproblems with my gms, new, 11 x6 prop good horizontal power, good idle but as soon as go vertical i lowers its rpms and dies.. i checked evrything , fuel lines , tank, clena carb , no air leaks well seated with teflon and oring, can you suggest what i could do.

can i just shorten the spary bar and clan inside it, but what is it , is it the pipe on the high speed needle end inside the carb

regads
david

RC-Captain

I don't have this engine but I may be able to help. Are you seeing a lot of smoke when idling ? Normally if you nose the plane up vertically and it dies, that means your needle is set too lean. Open up the needle one half turn and then see if it will run while the nose is pointed up.

PS nice name.

opjose

Like he said!

When the nose goes up the plane tends to lean out and speed up, and if not set correctly it may die out.

When nose down the plane richens out and tends to slow down. If it is not set correctly it may bog down and die out too.

Getting everything right means that you find the point where the engine does not die out in either position, preferably with only 1/3 to 1/2 tank of fuel in when you perform the test.

( Though remember that with the nose down you may be uncovering the clunk, if you follow the stock advice to not let the clunk travel forward... )

A Uniflow setup helps this somewhat.

RC-Captain

GO BACK AND READ WHAT HE SAID ! I SEE NOTHING ABOUT HIM MENTIONING THE NEEDLE BEING TO LEAN..........

JDW

Hi David,

If you have a look at my post on Page 13 of this thread you will see how I solved what sounds like exactly this problem. Others have also followed this proceedure and sorted out their GMS 47s.
You will find other posts suggesting that you need to drill out nipples, file the spray bar etc. In my opinion NONE of this is necessary and it wont solve the problem you have. I would strongly suggest you DO NOT modify the engine in any way.
If your engine can achieve good power while horizontal then it is obviously getting enough fuel so drilling out holes is, by definition, unnecessary.

davidsai

hi there that is what happens but the needle is open about 7 full turns from closed, tahs a lot aof turns,
is it posible that when in horizontal fuselage psotion it drwas enough for good all speed out and when nose up, it does not get as much fuel and dies very quickly, can it be a resricion of some strage sort , i have clenaed and checked al conections on fuel lines , can i open up the fuel niples at rear needle.?????

i have seen other people using this engine with this same prop that is teh 11 x 6

i will thinker a bit more with it today will let you know how it goes
reagrds
david

davidsai

hola estrda como vas how are things i a mi nbarranquilla did you finally buy the gms engine?
regards
david

Flyboy Dave

My Feedback: (21)

If your engine is not getting enough fuel, it will quit running in flight.
The fuel inlet may be restricted like mine was. If the fuel inlet is
restricted you will have to re-drill it so that the engine can get proper fuel flow.

From post #96:

Well, it looks like there certainly is an alignment problem in the fuel
inlet spigot. I put a short piece of fuel line on the carb and blew into
it with the barrel wide open. Even at 3 full turns out on the high speed
screw....it seemed like it was restricted, and hard to blow air through.

This picture wasn't easy to get, but you can see the partial restriction.
It's not really as bad as it looks, due to the angle I had to use to get
light into that small hole....the restriction is more like 40% (eyeball)
it looks more like 50% in this pic.

FBD.

Flyboy Dave

My Feedback: (21)

If you cannot get your carb drilled properly, you can get a replacement....

http://www2.towerhobbies.com/cgi-bin...?&I=LXEGM2&P=7.

You should seal the muffler seams with high temp silicon so that you will have
full pressue to the tank, Also make sure the pressure nipple is drilled properly,
so the air can get into the fuel tank.

If you do not have proper fuel pressure to the carb, you will have problems in
flight, such as engine quitting when you go vertical.....the engine will lean out
when you go vertical.

FBD.

opjose

As he said, if it runs horizontally, but dies in any other position, it is not a carb problem.

Look elsewhere.

Try running the engine on a test stand upright.

Then invert the engine, but not the fuel tank/system... keeping the fuel tank at the same level as the carb, when it was upright.

Watch to see what happens.

7 turns is far too open.

Do the 'blow' test directly into the carb bypassing the high speed needle.

Do the blow test with the high speed needle set as per the defaults in the manual...

I'll bet that the problem lies either in the fuel tank, the lines going to engine from the fuel tank or between the high speed needle and the carb.

Check that all of the nipples are tightly screwed in.

Make sure that the engine head is also fully screwed in ( these often loosen after the first few start ups when the engine is new and must be retightened.

JDW

David
The reason your needle valve has to be opened 7 turns is that your IDLE NEEDLE IS SET INCORRECTLY. This is exactly the problem I had - main needle had to 6+ turns open. After trying all the obvious checks (including looking for fuel restrictions checking sealing AND drilling out the muffler nipple !) with no change, I found to my great surprise that it was all down to the idle needle setting. I can reproduce the problem on any GMS 47.

Check that your muffler nipple is not totally blocked (i.e. blow through it) If it's OK just follow the proceedure in my post on Pg 13 for setting up the low speed (idle) needle and your problem will go away!

opjose

Yes very true.

The bottle neck so to speak becomes the idle speed needle.

You are best off returning both the low and high speed needle to the factory defaults ( assuming you have never overtightened it, thereby scoring it... ) then starting the engine and working from there.

RC-Captain

I have to agree with opjose, because if there was any restriction, it would die when idling. Do you have a tachometer ? If yes , please use it with the engine idling, and let us know the reading. My guess is it is above 7k rpm. If you can, set the engine back to break in settings , start the engine WOT being careful when starting and see if the engine continues to run. If yes nose it up... it may load up and flame out , if it does the turn the needle in 1/4 turn in until it runs nosed up . DO NOT TOUCH THE FACTORY LOW SPEED SETTING UNTIL YOU GET THE HIGH END SET.

spyder79

Hello Everyone!

I just stumbled into this thread while searching for something else, and was captivated by the subject and how it has unfolded, enough to read every post. I have a Tower .46 in a Sig Sealane and another in a Ace Seamaster. Both have been very reliable engines for me and have quite a bit of time on them. I have had a bit of the problem described, specifically the flat response of the high-speed needle. I believe it was due to some incorrect low-speed adjustment on my part, which I managed to sort out by trial and error. Overall, the Tower .46's have been powerful and reliable for me, right out of the box.

The evolution of this thread has prompted me to comment on a few things. I hope that maybe I'll be able to add something useful to the mix. First, I should mention that in the 3 years I've been flying RC, I've had little reason to mess around with these carbs, aside from careful adjustment and cleaning, so this thread really got me to thinking and got me to take time to really examine the carb in question. I've been turning wrenches for most of my life, from chainsaws to heavy equipment so I've spent my share of time tinkering with various types of carbs.

What I noticed right away is that there is a lot of similarity of operational theory to carbs used in some motorcycles, snowmobiles, and even those used on certain English cars. Many of these applications employ more sophistication, but they have a common attribute. I'm talking about the tapered-needle-in-the-jet arrangement. The thing that I find important here, and that nobody has directly stated so far, is the basic theory of this type of carb and how it applies to the subject of this thread.

The tapered needle concept is important because it continuously adjusts the fuel flow in proportion to the throttle opening, thus preserving a predetermined fuel/air ratio. At low throttle settings (idle to midrange), the clearance between the sides of the needle and the interior of the spray bar barrel determines the amount of fuel delivered. The taper of the needle allows more fuel to flow as the throttle barrel is opened and the needle is withdrawn from the spray bar. The air and fuel remain in proper proportion.

As the throttle is opened more the amount of fuel flow is greater. If not for the high-speed needle, the fuel flow would soon be excessive for the amount of air intake and the mixture would go drastically rich. But the high-speed screw works as a FUEL VOLUME LIMITER, so that when the throttle is open (WOT), the high-speed screw assumes full control over the mixture. This is assuming that the needle is fully withdrawn from the spray bar, or nearly so, so that the full amount of fuel passed by the HS needle is allowed to pass from the spray bar into the venturi. If the needle (which is being called the low-speed needle) is adjusted so it is still substantially inside the spray bar at WOT, it will be restricting the fuel flow and the high-speed needle will be ineffective, or nearly so. Opening the high-speed needle will have little or no effect because there is a downstream restriction, specifically the LS needle still blocking the spray bar. This accounts for the situation where the HS needle becomes fairly insensitive and has to be opened excessively to get a rich enough mixture at WOT (someone mentioned 5 to 7 turns!).

In a scenario where the LS needle is turned out excessively, allowing a lot of gap between the needle-end and spray bar-end, there will be plenty of fuel available at WOT providing that the HS needle is adjusted rich enough. The HS needle will retain the proper sensitivity since it will resume its proper role as a fuel limiter at WOT. The problem arises then at lower throttle settings because there will be excessive clearance between the sides of the tapered LS needle and the bore of the spray bar, establishing an overly rich mixture. This could also cause excessively rich mixtures at throttle positions somewhat lower than WOT because the needle will have left the barrel of the spray bar early. If the HS needle is then adjusted (mistakenly) by trial and error to achieve a decent transition, it will be running lean at WOT, possibly accounting for the flameout under load.

With these concepts in mind, it can be seen that the exact size and taper of the LS needle is carefully calibrated to deliver the proper amount of fuel at all throttle positions. But it should also be noted that LS needle position should be indexed in relation to the spray bar if is to perform as intended by the designers. Thus the measurement of the clearance between the LS needle and the spray bar at WOT. There is a little "wiggle room" in this measurement to achieve best tuning under varying conditions, but to stay within the original design parameters, it should stay fairly close, otherwise the transition between LS control at low throttle and HS control at high throttle openings will be compromised. After thinking about all this a bit, I remembered reading the owners manual for an old OS engine that lists a specific value range for this clearance. I would have to go through a bunch of paperwork to find it, but suffice to say that it exists.

With some of the other carbs I talked about earlier, particularly snowmobile carbs, the tapered needle is secured in the throttle slide with a C-clip that fits in a groove in the top of the needle. The needle contains up to 5 grooves to allow the needle to be indexed at varying heights to produce mixture adjustments for temperature and altitude. In many cases, other needle are available with different diameters and tapers to compensate for extreme conditions, or for engine modifications. As with the RC engines, making these alterations will affect the mixture and transition point from idle to WOT.

Back to RC engines and carbs, it can be seen that anything but the smallest adjustments of the LS needle will affect the idle mixture of course, but also the throttle transition point (between LS and HS needle operation), and possibly the WOT mixture (if the LS needle is leaned too much).

I think it is truly excellent that so many people have contributed to evaluating and solving this problem, coming at it from different directions and finding unique answers. I'm not trying to take sides with my observations, merely trying to fill in a few blanks. It seems to me that several people have danced on the edge of this in their posts, but I thought it was worth a bit of effort to explain the mechanics involved. Maybe it will help someone merely to understand their carb a little better. If you take exception to my comments, well...ROCK ON! Everyone is entitled to an opinion. Admittedly, most of my experience comes from other 2-stroke engines, as well as SU and Stromberg carbs, which are considerably more complex. Yet, it is easy to see that the same basic concepts have been used in the GMS and Tower carbs.

Regards to all,
Don

Turk1

Hi Don, though your explanation is excellant,I think you ignored the vacuum effect of engine because of the restriction of barrel to inlet air.I discovered it on cold days on my SK,when my full castor fuel got viscouse.Under half throttle engine was great but when I open throttle it begins leaner and leaner until engine stops.If I pull down the stick then engine recovers immediately.This was only because of vacuum effect.Now hot days I can lean my idle needle more safely without similiar symptom.

dishun

my gms .47 runs great at idle to midrange slightly rich then cuts out going down the runway at full throttle. I have checked fuel tank pickup clunk and fuel line to carb, line from exhaust to tank, no blockage or kinks in line. Engine has about two quarts of fuel run through. I am using omega 10% nitro. does anyone have any suggestions!!!!!!!!!

opjose

Your high end may be too lean.

The engine should be unloading as the plane picks up speed, causing it to run leaner, which in turn could be causing it to cut out.

Flyboy Dave

My Feedback: (21)

There are two things that are essential for our engines to run correctly, and they are
tied to each other.....no matter what anyone says.

One....you must have proper fuel pressure for the engine to run properly in all positions.
Did you read this thread ? This engine has a large muffler. You must insure that the flange
from the engine to the muffler is sealed, as well as the seams of the muffler to insure
you are getting proper pressure to the tank. The nipple from the muffler to the tank must
not be restricted.

Two....you must have full/non restricted flow of a proper amount of fuel for the engine to
run properly in all positions. If the fuel inlet to the carb is not drilled correctly, and has a
restriction, you will not have enough fuel flow. The engine may seem to be running
OK when it is not moving on the ground, however, it will lean out in flight, and then will not
have enough fuel flow.

What happens when these two factors are not proper ? The engine dies out for no apparent
reason. It doesn't matter how you adjust the carb....if you do not have enough fuel for all
conditions, your engine will lean out.....and in most cases stop running.

FBD.

opjose

This response was to a different query.

e.g. the one I responded to.

BTW: If the engine is properly tuned it will run inverted w/o muffler pressure.

I found this out when my muffler came off in flight.

RC-Captain

have you done your airplane nose up test ? before taking off ? and don't be shy about trying different props, especially the one recommended for breaking in the engine.

Flyboy Dave

My Feedback: (21)

....no kidding ? Try taking the plane straight up vertical and see what happens.