RE: GMS Engine Tuning Problem
 

Hi Longdan,

Can you share with us what is the typical number of shims for the different fuel content in your experience. Example, how many shims for 0% nitro? How many for 5, 10 and 15?

Thanks for your help.

Fly4Fun,

Wayne Miller

RE: GMS Engine Tuning Problem
 

I use 10% nitro and only one shim. Mind you the engines I have are all second hand but run great. My GMS47 outlasted an OS46AX. Same plane, same prop, same fuel, same abuse. The GMS lasted a further 12 months of use before the bearings needed replacing, at least the GMS didn't eat them and destroy the piston....

RE: GMS Engine Tuning Problem
 

If I had a tach and had kept some records, then I could share some data with you, but unfortunately, I have neither. I can only tell you of my own experiences with them. My 47, I ran from new on 10% Sig Champion and a few other 10% blends. It kept on getting better and better, long after it 'should' have been run in. I tried a few different plugs during this time, not through blowing them but just because I like to experiment. The best plugs I found were Model Technics Max Flash plugs made in England. These things lasted the distance and performed their job exceptionally well. The OS plugs are easier to get, which is why I use them. I plan to order some hot Model technics M6 & M7 plugs soon.
Several months ago, I switched to 0% FAI fuel (due to it being cheaper) and have never looked back. I don't know why I ever bothered with nitro (except for my 1/2A engines). I knew that the 0% needed higher compression, and so I gradually removed head shims. The 47 would run with all 3 shims on 0%, but it wouldn't idle or transition well, so out came some shims. Performance improved, but it still died at idle, so in went hotter plugs. Eventually I settled on what I have now - 1 thick shim and a hot plug. Most of this testing was done at the field, tuning up in the pits prior to a flight. Deadstick? take out a shim and fly. Bad idle or transition? try a bigger prop. Idles well, but wont make full revs? change the plug.
A lot of this went on. But something that all people should take note of - what worked for me didn't always work for other GMS .47 owners (there's a few of them at my club). Many other factors came into play, like fuel tank set up and height (filter or no filter), cowled or uncowled, drilled or undrilled carb, rear needle valve or carb mounted NV etc. Another major was prop selection. I found that on finer pitched props, I got better performance and easier starting by going to a cooler plug.
Please be aware that I am no expert when it comes to glow engines. These are just my own experiences. A year ago, I was flying a trainer, and I have crashed a few 'second planes' since then. But, I am a good listener (to the old guys at the club), and I dont have a problem with stripping an engine right there at the field. I have said to other guys that I see are having tuning problems 'why not take a shim out' or 'why not change the prop'. They say 'OK, i'll get in on the bench at home and try that'. The next weekend, I'll ask them how it went, and they say they didn't get a chance to do it, and their engine is still running badly. Or they got it going well on the bench, but once it's back in the plane, it still runs like a dog. I'm a big advocate of 'field testing'. While the other guys are gasbagging about the latest ARF, I'll have the head off. Eventually they wander over and say stuff like " Gee, that's a lot of work to be doing at the field". I say "If I don't do it now, it'll be another week before I know if the changes are any good ot not".

The bottom line is that you need to test suff for yourself and arrive at your own ideal setup.

RE: GMS Engine Tuning Problem
 

Very good advice! Also, go over the engine a few times after it is run up to operating temps. I'm now opening up all of my engines to look inside for debris left in from the assembly line.

RE: GMS Engine Tuning Problem
 

Here is where I ended up...sorry I dont have a "before" pic, but the needle was recessed into the end of the spraybar when @WOT.

RE: GMS Engine Tuning Problem
 

Why didn't you just unscrew the low speed needle valve a few turns to 'shorten' it?

RE: GMS Engine Tuning Problem
 

I thought about that quite a bit. The needle has a slight taper to it. If you simply unscrew it, it will allow more fuel through at idle, however, at WOT the tip is recessed into the spraybar, thereby impeding clean fuel flow. By shortening it slightly, the taper contacts (or comes close to) the spraybar in the same (screwed in) position even though the actual tip (almost) contacts the inside of the spraybar farther out (obviously 1mm). However because it is shortened, the tip now clears the end of the spraybar, at WOT, which allows full unimpeded flow from the spraybar.

If you just screw it out a ways, then you dont get to screw it in if you need to lean the low end.

Im not technical about this. Im just trying to glean the sensible information off here to get my engine to run well:D Perhaps this wasnt needed, I also drilled out my fuel nipple/spraybar tube at the same time.

This was a recomendation of XJet. Made good sense to me. Remember what my problem was. I couldnt get the engine to run a rich 4 stroke, even with the needle out in my hand! It was obviously fuel starvation and these seemed to be logical steps to over come that in my case. And they worked, but thats me;)

RE: GMS Engine Tuning Problem
 

I have a gms 76 pro ringed engine and it took me about 2-1/2 weeks to get it broke in properly it now runs like a charm and it is one of the easiest engines to start that I have ever owned . run it rich for the first few runs and then lean it just a touch for a few minutes at a time with cool down time in between runs . good luck and safe flying

RE: GMS Engine Tuning Problem
 

This is such a wonderfully informative thread. It is amazing in it's helpfulness and scope. I started RC glow way back in 1979 and quit in 1981 due to the expense(crashed airplanes and the distance to Sepulveda Dam Apollo Model Field, 15 miles). Now after getting back into RC via electric planes starting last year, I just had two Hobbico Twinstar ARF's with 2 Magnum .28 glow engines and the associated paraphernelia delivered to my door a few days ago. One Twinstar is going electric, one Twinstar is going glow powered and also ;)a third I just ordered yesterday is a crash reserve. At $109 per Twinstar(no sales tax) and free shipping with my new membership plus the $25 instant discount, I came out a winner with this cheapest twin I could find on the market and the reviews say that it flies good too. I have not done anything yet due to schedule. However, I have been reading a lot on tuning glow engines. This thread by far is the most far reaching and comprehensive on glow tune-ups.
The RC 2 stroke glow engine has been around for over many decades and yet I find the material discussed in here thoroughly fascinating and eye opening. Wow!!!! the idle could be running reliably and yet be out of adjustment. As simple as pinching the fuel hose while idling and catching the slight change in RPM allows correct idle setting. Did not know that helpful tip till I read this thread. Then the interaction between the High Speed Wide Open Throttle setting could affect the idle setting and thus the need to revisit the idle adjustment and then vice versa for the High Speed adjustment until both are adjusted correctly with the transition resulting in smooth as silk action. I always thought from my days of 1979 RC glow flying that you set the W.O.T. adjustment and then the idle adjustment and that was done (I had bought brand new and flown these Super Tigre .60, OS .35 & .25 and Thunder Tigre .25 with no engine performance issues at all back in 1979-1981). Well as noted in this thread I was just lucky way back then.....because as correctly explained by some wonderful guys in this thread that there is a certain amount of interaction between the High Speed setting and the idle setting IF...IF......IF...the low speed needle is still slightly inside the tip opening of the spraybar at WIDE OPEN THROTTLE. This has the effect of restricting/obstructing the fuel flow at W.O.T. at the spray bar tip regardless of High Speed needle adjustment. This is the reason why on SOME ENGINES WITH THIS CONDITION, the HS needle is already backed out till it almost falls off and it still has no effect on the W.O.T. setting. The Low Speed needle still intruding into the spraybar at W.O.T. is effectively regulating the fuel flow even with the HS needle fully backed out. Thus the engine leaning out and quitting at W.O.T. (especially on take off with full power on and on high speed flight). One persistent fellow's solution is to look down into the carburetor throat and back out by .002-.004 the intruding LS needle tip away from the spray bar opening tip and thus remove the obstruction at W.O.T. Others have a different problem, like one fellow has misaligned fuel passageways, another has out of range glow plugs, another has too small a prop allowing too high a W.O.T. rpm probably RPM'ing out of the maximum fuel delivery calibration set by the manufacturer for that size carburetor spray bar, fuel tank installation too high, too low or too far. For me the most fascinating is the Low Speed needle intruding into the spray bar opening tip at W.O.T. thus causing a fuel flow obstruction at W.O.T. making the High Speed needle unresponsive even in some cases backed out nearly all the way. With the wealth of astounding tips in this thread, I am more and more confident that I will be able to fly those twin .28 Magnums on my Twinstar and avoid engine performance/reliability issues. You guys are wonderful, saving many, many of us from countless frustrating hours trying to fix engine issues that after completely reading this thread from start to finish makes the obvious sense. You guys deserve our appreciation and thanks. God Bless y'all.
larrysogla;);)

RE: GMS Engine Tuning Problem
 

My gosh Larry...that was quite a mouthful for a third post:D

These issues are with the GMS engine only, and these are quite serious engineering flaws that we are dealing with here.

That being said, you shouldnt have any "performance/reliability" trouble with other engines, and certainly not like this.

Update: Mines runnin like a screamin banshee, strongest "46 class" motor I have had by far:D

RE: GMS Engine Tuning Problem
 

....yep. I must say, mine is running great too....

....no dead sticks....mucho power, for an inexpensive engine. ;)

FBD. :D

RE: GMS Engine Tuning Problem
 

Other than the air leak that won't let you shut them down, I've not a word of complaint about these engines.

Yes, they can fuel up at low speed but then I consider them quite 'sporty' and a little more powerful than their OS equivalents (.32 and .47 in particular). I spend my time flying above 50% throttle so it's not a concern.

RE: GMS Engine Tuning Problem
 

Hi,

For some reason I haven't been notified of the latest posts, I just thought I'd check. I found new posts and I enjoyed getting caught up with the latest comments.

My GMS's are all working great, and I'm glad to see others are able to get theirs working well and are enjoying them. The last problem I had was when I tryed to run old fuel, worked great on the ground, but died 1/2 way through flight - of course I screwed things up by trying to adjust the carb for it, but after getting new fuel and a few minor adjustments, all was well again.

I hope everyone is enjoying their GMS as much as I am.

Fly4Fun,

Wayne

RE: GMS Engine Tuning Problem
 

Heya Wayne, I run old fuel all the time when people give it to me. Just gotta mix a little in at a time so you get the milage out of it but it doesnt upset anything;)

RE: GMS Engine Tuning Problem
 

<table id="post18312847" class="tborder" align="center" border="0" cellpadding="5" cellspacing="0" width="100%"><tr valign="top"><td class="alt1" id="td_post_18312847" style="border-right: 1px solid rgb(167, 167, 167);"><div class="smallfont"> Best Glow Plug for a GMS 47? </div> <hr style="color: rgb(167, 167, 167); background-color: rgb(167, 167, 167);" size="1"/> <div id="post_message_18312847"> I have a GMS 47 with one gallon of fuel on it and the original "long" plug that came with the motor. I want to buy a back up glow plug, but I don't know what it is. I tried a "Fox long plug standard" but it didn't work very well. Tried a "Tower Hobbies Standard", but it didn't work very well. Tried a "K&amp;B long standard" same story. Each flight has been in 60 - 65 F weather conditions and pretty humid. Any suggestions would be appreciated. Motor works great off of the original "break in" long plug. If only I knew what it was I would buy another! I bought the motor NIB on RCGroups classifieds. Advice and your experience appreciated. Thanks!

Best plug in hot weather? Cold weather? What's your experience with this motor? </div> </td></tr><tr> <td class="alt2">
</td> <td class="alt1" align="right"> http://static.rcgroups.net/forums/im...tons3/edit.gif</td></tr></table>

RE: GMS Engine Tuning Problem
 

OS #8. Works perfectly in all weather. You can try other plugs, but if you want it to work first time, just stick in a #8 and go fly.
I have also had good success with [link=http://www.modeltechnics.com/glowplug/maxchart.html]these[/link] plugs, but not sure if you can get them in the states.

RE: GMS Engine Tuning Problem
 

What fuel are you using?....

Sorry to ask (no offense intended)...but have you adjusted the carb after you changed the plug? tower plug should work without problems on that engine...

RE: GMS Engine Tuning Problem
 

I second the recommendation for OS plugs. Not had a problem with any of my GMS engines.

RE: GMS Engine Tuning Problem
 

Best plug in hot weather? Cold weather? What's your experience with this motor?

I'm using Sig 10 % nitro Champion Fuel

10% Nitromethane
20% Lubricating Oils
(1/2 Castor, 1/2 Klotz)

Also using an 11 X 5 MA Prop. Mostly cold days here so far. 60 -65 Degrees. Wonder if Summer will ever come.

RE: GMS Engine Tuning Problem
 

I have always used the OS A3. The #8 I saved for my larger engines. The 11X5 Master Airscrew has a lot of flex in it and won't let the engine wind up. Try the APC 11X5. I think you will like the performance.

RE: GMS Engine Tuning Problem
 

Hi,

All the plugs mentioned are good. I personally use the Fox Long plug with the Idle Bar and I have never had a problem.

When I have tried other plugs, I've had to change my carburettor adjustments just a little, but they all worked well.

Fly4Fun,

Wayne

RE: GMS Engine Tuning Problem
 

Thanks for all the input!
Looks like I need to adjust the carb and go for an OS # 8

RE: GMS Engine Tuning Problem
 

What flaws?

I can't say I have run into anything amiss with either the Tower Hobbies rebranded engines nor the GMS engines.

I wish Tower kept selling both.... they do seem to require a longer break-in period.

RE: GMS Engine Tuning Problem
 

hi all
it was about five years ago, I have similar problem with my gms 1.2 . I saw when I prime the fuel goes to carb but goes back to the tank when stop primming. what i'v done was installing one way valve before carb inlet. and it's working for me.

RE: GMS Engine Tuning Problem
 

Can't believe this thread is still alive. I just put my old GMS .47 on a Spot On 50. The engine never did run very well. I drilled out the carb inlet and removed the remote needle valve and I am using an OS muffler. It is running pretty well now and it starts right up after it is warmed up. I needs a little more power though.

I am going to try a Vess 12x6 next flight. Wow that prop is light! My APC 11x6 is a little lacking - might need a bigger engine though for this plane.

The check valve looks like a good idea adji. I hate when it does that. I wish I would have thought of it when I was running little Norvels.