RE: GMS Engine Tuning Problem
 

Wayne:

The concept of the pressure and pickup line being on the same clunk baffles me a little. Wouldn't the pressure and flow cancel each other???

I know what you are saying about the fuel loss through the muffler. I suspect there is some. The throttle was so steady and predictable, I don't think I was loosing any through the carb. As I mentioned, I tried the check valve in the pressure line, and that did force fuel into the carb. A bleeder valve of some sort that directs the fuel somewhere else, maybe to a 1 oz. tank that is open to air pressure, is the only solution I can come up with. I don't think I lost much fuel throught the muffler, as I was still up about 10 minutes (10 oz. tank) and I did not notice excessive oily discharge on the tail.

I am anxious to hear your thoughts after playing with the setup. This setup may even tame down the engines without the carb modification. Well, ...maybe that is hoping for too much.

Dave:

I have thought about those bladder tanks too. If I am figuring right, the expansion of the bladder would be a lot like the pressure relief valve I am proposing.

Andy

RE: GMS Engine Tuning Problem
 

Hi Andy,

I found many articles on making uniflow tanks. Some of the articles show the pressure line and pickup line linked to one clunk. I did a quick search and althought the following article is for control line, it is the same for RC - here is the site:

http://home.cogeco.ca/~controlline/tip1.shtml

You'll have to scroll down the page a bit before the pictures start to show. Using two clunks may be better, but I like this idea.

Hope this helps.

Fly4Fun,

Wayne Miller

RE: GMS Engine Tuning Problem
 

Now I get it, I thought you had both lines plumbed to one clunk. In reality, one clunk is holding both lines down, though plumbed to only one. The only catch I can see is that you better use some light tubing, or the clunk may levitate a little. Other than that, I like it![8D]. Thanks Wayne!

Andy

RE: GMS Engine Tuning Problem
 

Well, got to the field with the drilled carb, and while it was improved, it still is a poor performer for 3d use. I'm going to try resealing the backplate and the carb to block junction, but I'm beginning to give up hope of this ever being a good 3d engine.

RE: GMS Engine Tuning Problem
 

Hi Dean,

What prop and fuel are you using?

Please keep us up to date on your progress.

Fly4Fun,

Wayne Miller

RE: GMS Engine Tuning Problem
 

12x3.75 apc and omega 10%. The peops different, but thats the same fuel I've always used in it, and yes, its a new jug.

RE: GMS Engine Tuning Problem
 

I'm glad to have found this forum since i've been having problems with my GMS-76.

I found some tips about a year ago, to seal up the engine, and have done that.

Mine was running hot and quitting at full power.
i was about to trash it.

i'll try these tips and see what happens.

My application has the engine mounted pointing up, with a tank mounted "tubes up" on the engines' belly. I do have some foam between them.


THANKS.

RE: GMS Engine Tuning Problem
 

Is your fuel inlet restricted ?

Dave.

RE: GMS Engine Tuning Problem
 

yes, it was as shown on a picture in a previous post.

After this fix( we'll see if it works. I believe!) my next big problem is vibration caused by the engine that is affecting my gyros "GWS-P03".
But, i'm sure that's for a different forum.

RE: GMS Engine Tuning Problem
 

Here's a picture...
GMS-76
I selected it for it's rated thrust to weight.

[img][/www.geocities.com/rssql/bucket1.jpg]

RE: GMS Engine Tuning Problem
 

Dean, I hope I can talk you into not giving up. It is my opinion that drilling the carb may make the adjustment a bit touchier to achieve. I recommend replacing the carb body before giving up. There is a lot of talk about leaks in this engine, so I wanted to see what was really going on. I took and old glow plug and drilled it out and tapped it, to fit a nipple. I then installed the modified plug in the engine. I was then able to submerge the engine, with the muffler and carb blocked off and see where the leaks were. I expected bubbles around the throttle barrel, but only had one or two in a couple minutes time. That isn't enough of a leak to matter. I had a steady stream of bubbles around the base of the carb. I found that the rings around the carb throat were very stiff.(referring to my friends .47, not mine) I went to True Value Hardware, and purchased some new rings for the base of the carb. Some of these engines have two O-rings. One at the base of the carb and one inside the throat, where the carb slides in. If you have two, change both. This solved any problems with the engine not wanting to shut down at idle. There were no leaks at the backplate or head gasket. After drying the engine out, and drowning it in Marvle Mystery Oil, I put it on a plane and went flying. Between the new carb body and the new O-rings, the engine ran beautifuly!

Now, the 3D thing! You may have noticed my posts on the uniflo tank setup. I had a friend fly my .47 with the new tank. He is a 4-stroke guru. He could not believe the performance coming from a 2-stroke. After doing a lot of hovering and 3D stuff I don't know the names of, I asked him what he thought of the engine/tank combo. He had one word for it, the that was SMOOOOOOOTH! I can't explain the difference, but you can really feel it!

As far as the one clunk or two clunk uniflo, it has to be two clunks. The single clunk design works well for control line, because you want the clunk at the edge of the tank, at the outside of the flying circle. Tying the two lines together allows this kind of control. Since an RC plane uses all three axis, the clunk has to be able to free float to every corner at the back of the tank. The only way to do this is to have one clunk for each line.

Dean, I don't know if it is worth a tank of gas to you, but if you want, order the carb body, and when it arrives drive up to Appleton for the day. I will help you get the demonds out of your engine. You can fly as my guest with the Valley Aero Modelers, provided you have AMA insurance. Let me know!

Andy

RE: GMS Engine Tuning Problem
 

Andy, thanks for the very kind offer, but it may prove unneeded:

update!


I resealed the carb using rtv, got to the field and noticed no improvement. :(

Flew it a few times, adjusted more, but just not good. Then it dawned on me, the fuel filter.

I had swapped in a new cheapy disposable fuel filter when I put this plane together and now it was about the only thing left untouched, so off it came and replaced with tubing.

I immedietely knew it was improved, and had to lean out the idle jet a bit and the main a whole lot! Pointing the nose up no longer made much difference at all, and I was able to get way more revs on the ground now. Airborne, it was a whole new motor, running far better than ever before, ( hover to outside loop back to hover without going anywhere is fun! ), but still a bit soft in the midrange. That might be just a fine tuning on the jetting issue though, I say might because I landed a bit hard when I came down to adjust and broke my only prop :eek: , so fine tuning efforts are going to have to wait a bit.

I might get another airborne opportunity this wensday, but this looks like the filter might have been the problem the whole time. Aargh!!! [:'(]

Dean in Milwaukee

RE: GMS Engine Tuning Problem
 

Glad to hear it Dean! If the midrange stays sloppy, try the new carb body or the uniflo setup or both. It should tighten it up a lot! Good luck!

Andy

RE: GMS Engine Tuning Problem
 

Wayne:

If you get a chance, see if there is any way to get the new thread entitled GMS 47 directed to yours. Everything we have been through the past several months is being rehashed. If its readers could be sent this way, this thread will save them a lot of agrivation.[:@]

Andy

RE: GMS Engine Tuning Problem
 

Hi Andy,

I posted over there and referenced this thread, thanks for the suggestion.

Also, if anyone else has had good results from reading this thread, would you let us know, we would greatly appreciate any feedback - thanks.

Fly4Fun,

Wayne Miller
Pres. K/W Flying Dutchmen
MAAC 6166

RE: GMS Engine Tuning Problem
 

Thanks Wayne!

Andy

RE: GMS Engine Tuning Problem
 

Update on my GMS-76.
I drilled out the carb nipple, and the hole under the nipple.

It seems to perform better, does not die in WOT like before.

I still have fuel foaming in the tank due to vibration, due to running it near WOT most of the time. That's the only way it's going to get off the ground.

http://www.geocities.com/rssql/bucket1.jpg

RE: GMS Engine Tuning Problem
 

Got a bit more flying in today, and some fine tuning. The verdict is the motors running pretty decent now, not perfect, but pretty good. I will probally try out the uniflow setup next to try and make it better yet.

Interestingly, I gave a 11x3 apc prop a shot, and I think I like it better than the 12.25x3.75 prop. While thrust is down a bit, theres still plenty to do pretty much anything, but what makes it nicer is the motor responds faster I thnik from a combination of the prop being lighter and easier to rev, and the lesser load also allows it to rev into a higher hp rpm range before the prop really starts to load it down. The net result is the throttle response seems snappier.

More experiments to come.

RE: GMS Engine Tuning Problem
 

Another update:

Was flying few days ago, the motor running aceptably, just cruising around at abut 1/2 throttle when the motor suddenly died. I deadsticked it in safely and found that it would start easily, but die instantly the moment I got the ignitor off. This on an engine that always started and idle'd flawlessly.

I ran out of time there, but at home decided to swap over to the uniflow system, and also bored out the nipple on the muffler. There did'nt seem to be enough meat on the carb nipple to do the same, so I left that one alone.

Now the motor again starts and idles very nicely, and after fiddling with the main jet, got it doing 14,900 rpm with the apc 11x3.

The problem now is that no matter what I do with the main needle, the motor will bog and die as the nose comes up. Making it super rich gives a short time delay till it dies completely, but it will die.

I'm baffled. The motor runs better than ever as long as its level, but worse than ever when the nose comes up. I can't belive how much time I've spent on this problem already, and its still not solved. :(

Thoughts anyone?


Dean in Milwaukee

RE: GMS Engine Tuning Problem
 

Dean,

If you engine dies when you take the glow plug ignitor off, you have a bad glow plug. Remember, a glow plug is a catalytic device and the coils can become contaminated. At this point, they will fire the mixture when a battery is attached, but won't work well after it is detatched. Many people think the plug is good just because you can hook up a battery and start the engine. This is not necessarily so. Try changing your plug.

RE: GMS Engine Tuning Problem
 

"Try changing your plug."


Did already, new #8 OS ran exactly the same as the old plug.

I did some more fiddling, found that the uniflow setup created air bubbles in the fuel line. Swapping back to the standard setup got rid of the bubbles, and helped some in runability, but its still poor with nose up and strong with nose level. The great idle is back as well.

I'm starting to think I should just sell the whole damn thing. :(


Dean in Milwaukee

RE: GMS Engine Tuning Problem
 

Hi!
To me it sounds as if you run too much nitro!!
Engines developed for low nitro fuel behaves like you describe...sudden stops at all throttel settings and general erratic engine behavior.
Try 5% nitro and an Enya 3 glowplug.
A uniflow tank is what I recommend, it has two clunks running parallel to each other, with one hose a little bit shorter than the other.The long hose is going to the carb, the short one to pressure nipple on the silencer.
But the best tank available is the Tettra "bubbleless tank". No air bubbles could get into the fuel if you use one of those!

Regards!
Jan Karlsson
Sweden

RE: GMS Engine Tuning Problem
 

I'm using 10% omega, and gms does recommend 5 or 10%.

I don't think its the nitro load because if the plane remains level, it'll run wide open perfectly till the tank goes dry. Its when the nose is raised that the trouble starts. It immedietly leans, prodcuing a momentary increase in rpm before it starts to die. If you drop the nose quickly enough, it'll recover and rev back up again.

This same test holds true at reduced throttle positions, but the effect takes a bit longer to occur.

Like I said, its a mystery.


Dean in Milwaukee

RE: GMS Engine Tuning Problem
 

Hi Dean,

Your problem to me sounds like an air leak, either at the carb "O" ring, backplate or pin hole in the fuel line. If it is a pin hole in the fuel line, or an air leak in the fuel delivery system, you will see air bubbles in the fuel line when the nose is up at full throttle. When you put the nose up, the fuel draw is much greater by the carb and you can see if it is drawing air into the line - if so you know the problem is in the tank or fuel line.

If the carb, or backplate is leaking, you can find it when the engine is at full throttle by spraying WD-40 around the base of the carb or backplate, if the RPM changes - that is where the leak is.

I noticed previously you had a problem with your fuel filter, do you think you might have a partial fuel blockage in the needle valve area from the old filter? Just a thought.

Also, I only use 15% nitro with my GMS - I'm not sure if that will make any difference.

Thanks for keeping us up to date, wish we were closer, I'd like to give you a hand and see if we could get to the bottom of the problem.

Fly4Fun,

Wayne

RE: GMS Engine Tuning Problem
 

If the engine dies a couple seconds after you remove the igniter from
the glow plug it's a sure sign your fuel in no good. ;)

FBD. :D