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Carburettor Set Up

Do you know how to set up a Thunder Tiger GP 61?

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Rob Cope16/09/2007 21:15:00
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94 forum posts

Hi All,

Help needed here.  I have a second-hand model with a Thunder Tiger GP 61 installed in it.  It has one needle valve and two other adjustment screws.  I have no manual, so don't know what to adjust for each reason, when and in what order...

I have tried to find manuals, but I'm having no luck.  The engine won't run at all well at present.  As it's inverted this is a big problem.  It currently starts rarely - and then needs to run far too rich in order to even get it to full throttle without dying.  I've re-plumbed it - no change.  It keeps cutting out.

I wonder if anyone has some information they could pass on to me from their manual?  It's an older model with the "straight" needle valve (close o the prop arc) not the new angled one.

Thanks in advance,

Rob

Tim Mackey16/09/2007 21:26:00
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20919 forum posts
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15 articles

Needle valve controls main mixture, and a good starting point is around 1.5 turns out from fully closed. The other two screws are idle mixture, and probably throttle rototr stop /guide.

Set the idle mixture also at around 2 turns out, and then get her running, open throttle wide, and set needle valve to give maximum revs, then turn it out about .5 turn from this position, so that it slows just a little.

Leave this needle valve alone from now on.

Throtttle down to idle speed, see how it runs, and especially how it picks up upon opening the throttle quite quickly, if it is lumpy / smokey / oily or just coughs and dies, then probably too rich, so turn in the idle screw VERY SLOWLY and by VERY small amount, open it up again, and see if it is worse or better. If better, keep screwing in until idle is steady and pick up clean, if worse, screw it the other way in small steps, observing pickup and idle as before. HTH

If the iidle screw is air bleed type ( and  dont think it is on these ) when I said screw in - screw it out, and vikky verkky

Rob Cope17/09/2007 09:21:00
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94 forum posts

Much obliged Timbo,

Thanks for the help. It may be an air bleed idle mixture set screw after all (someone helped me identify it) as there's a little port drilled at the front of the carb where the tip of the screw will "act". Does this sound right? I'll try to get a photo organized if that will help. Do I simply write the photo URL into the page? Oh, I see there's a button for images

Looking at some of the adverts for the new GP 61, they're recommending 10%-15% fuel. I'm using 5%. I thought high nitro was just for performance rather than a requirement (other than four stroke engines.) Should I switch to 15% nitro do you think?

I have had the advice to leave the needle valve alone once it's "set" before - and I apply it to my Irvine 53 fine. However, unfortunately the GP 61 seems to "wee" fuel when waiting at the field and in transit unless I screw the needle valve shut. This may be something to do with my having to run it so rich at the moment. What I propose to do is count exact quarter (or even eighth) turns when closing it and re-open the exact same amount before starting. This is a bit klutzy, but it may work for me. I might need new O rings for the valve in 12 months though!!

Now this may indicate incorrect tank height as I understand it? What I've seen is that the _full_ tank level should be the same height as the needle valve (or spray bar whatever that is? I guess it's "inside" ) However the spit (I think it's a Sportsman Aviation 64" ) has the engine inverted. This level "rule" gets tricky with inverted engines started right way up (plane inverted) unless the tank is only half filled for each flight.

I have renewed the "pressure " and "filler" tank plumbing. Perhaps the card feed needs doing too. I will go and buy some "top notch" fuel tubing and redo all three I think.

Thanks,

Rob

Tim Mackey17/09/2007 09:48:00
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20919 forum posts
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My 64" S/A Spit has the SC 91 $ stroke motor fully inverted, and exhibits no problems, with the tank CENTRELINE just slightly BELOW the spray bar ( which is effectively the same position as the main needle valve). Sounds like an airbleed type idle - so turning IN will reduce the air and consequently RICHEN the idle mix.

Photos need to be uploaded from an Image host site such as Imageshack see here.... http://imageshack.us/

Forum guys tell me they are working on a direct image posting facility soon

I do actually run tank pressure on the Spit. Forget the amount of fuel in the tank as a culprit, just set the tank height as described, and it should be fine.

Probably the excessive height at the moment is causing the "ground flooding"

Keep us posted... T

Rob Cope17/09/2007 16:24:00
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94 forum posts

Thanks one again,

You guys on here really are kind.  Here's the photo.

http://img267.imageshack.us/img267/7595/pict0200annsmaj7.th.jpg


Yellow, I think secures the throttle barrel.

Green looks like the idle adjust screw (note the small hole central to the intake - air bleed)

I cannot work out what Red might be...

Regards, Rob 

Lee Hewkin17/09/2007 17:11:00
2 forum posts
I think you will find the red adjusts the gap on the air intake so it does not fully close when throttle  is shut down , lets you have tickover yellow and green are correct as per Rob from Lee
Lee Hewkin17/09/2007 17:16:00
2 forum posts
[img s=6050]http://www.modelflying.co.uk/members/images/faceit.gif[/img] UploadI think you will find the red adjusts the gap on the air intake so it does not fully close when throttle  is shut down , lets you have tickover yellow and green are correct as per Rob from Lee
Evan Pimm 218/09/2007 06:55:00
51 forum posts

Yes, the red one is the idle stop screw. If you want to stop the engine from the tranny you will have to screw it out far enough that the engine will actually stop with the throttle stick right back and the trim also right back. Some experimentation will be required.

Evan. 

Rob Cope18/09/2007 12:00:00
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94 forum posts

Thanks all,

That all makes sense now. I can go play with the red screw freely and check out the end-stop action. Phew! I do want an engine cut on the tranny, so I'll check I can close the air intake fully.

I'll put some pipe cleaners through the thing too later in case there's some gungy stuff lurking in there.  Are pipe cleaners "safe" or do they drop more fluffs than they clean out???

I hope I'll have some good news soon

Regards, Rob

Tim Mackey18/09/2007 14:58:00
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20919 forum posts
304 photos
15 articles
I wouldnt bother with pipe cleaners, just flush it through with some clean fuel, or even petrol.
Rob Cope18/09/2007 22:51:00
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94 forum posts

Hi Timob, Lee, Evan,

Thanks ...so... much!

I ran it this lunchtime. Eventually I adjusted the air-bleed (green) to one turn back from tight shut, the needle to 85% of a turn open - and Whoa! It fired and ran like a good-un. I can't say what full throttle will be (because of the baby next door) but it went right after a flick from the chicken-stick finger guard up to half throttle just like that. Not at all its behaviour prior to this.  You made all the difference...

Thanks ever so much for all your help. It seems tinkering with the green screw is the right thing. I'll let you know... But I am one happy chap so far .

Regards, Rob

Tim Mackey18/09/2007 23:03:00
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20919 forum posts
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15 articles
Glad to hear it, even if the neighbours aren't
Rob Cope21/09/2007 20:28:00
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94 forum posts

Hey!

It's often something quite simple, but unexpected isn't it?  Well,...   I'd kind of assumed most things were right and proper on this spit, but it turns out that the throttle control horn is anchored to the throttle barrel end, not with splines, but using _friction_!!!  Now the throttle horn screw had come a "little bit" loose and this is why the model wouldn't run properly.  The toe-bone wasn't connected to the knee-bone (on the throttle servo.)

I've tightened it up and suddenly the thing is starting to behave rationally under radio control!

D'Oh!  Always check _every_ part of a second hand plane for the unexpected... I haven't given it a thorough test (neighbours) but it's suddenly feeling like and engine rather than a wishing well...!

One more post after Saturday's flying-field test - hopefully not to report a crash!  Thanks everyone.

Regards, Rob.

Rob Cope26/09/2007 15:32:00
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94 forum posts

Well,

I did the maiden flight of the spit on Saturday, and carted it round the sky with the wheels down.  A club authority suggested not retracting them on the first flight.  It went well, but the engine cut as I was "flying" into the landinng and I landed short in the rough, but noly nosed over at the last instant.  One flight and no breakages.

I just had to have another go on the same day...  Second flight, I retracted the whees and boy it's a nice plane.  WYSIWYG - it's amazing (what you stick is what you get.)  Wherever you point her, when you leave the controls, she maintains attitue and roll.  Wow!  A bit different from a trainer eh?  Anyway, I was fool enough to try a loop and she made it to the vertical and ran out of oomph!  I just about peeled over into a small dive and recovered before the ground contested my rights.  I tried again later a bit higher up with a gentle power-dive beforehand... and she did the loop - nice and graceful.  Again, none of this tendency to flip over quickly at the top like the trainer.  I think the weight must be just right.  Anyway, shortly after the loop... you guessed it, the engine cut.  I managed to let her drift away enough to lose height and bring her round into a smooth langin (wheels down) and just nosed over again (even though on the strip this time) because I forog up elevator as she slowed.

So, you see, the engine problems are not over after all.  It keeps cutting out and a .61 2-stroke should surely be strong enough to climb this baby out at more than about 30 degrees and loop without a dive to pick up speed.  Am I wrong?  Do I need to upgrade to a 120 4-stroke anyway?  Once of the instructors at the club says the engine sounds a bit tight and might need running in.  I'm on to that task now, but somethign's not right.

Regards,

Rob 

Tim Mackey26/09/2007 16:00:00
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20919 forum posts
304 photos
15 articles

Well Rob, at least you have a had a taste, and she is home in one piece - thats always classed a successful flight

First off, - the nosing over is a bit of a familiar problem I am afraid, especially if the strip is less than VERY short and smooth. My 64" Spit tends to do it a lot, and it really spoils the elegance of the whole flight doesnt it ! Mine even does it with FULL up elevator applied on the run off, but I suspect I know the reason. Firstly the geometry of the setup tends to show a lot of warbirds up like this, secondly, the wheels, if anywhere near scale are WAY too small for grass, and thirdly, I have set my wheels up with a fair bit of friction to stop it rolling on for ever which it tends to do ( bit overweight and no flaps I am afraid so trucks in a bit quick ) and I use the retaining collets to push the wheels hard against the stub axle to slow it down on the ground.

Your .61 2T should be fine ( whats the AUW incidentally ? ) and even if you did fit a 4T, a 91 would probably be better. IMO any half decent warbird should never be fitted with a high revving 2T ( stands back and awaits the flak ) The engine may well still be a little tight, and therefrore you are unable to lean it out to peak power setting.

It would not hurt to go to 10% nitro, but in my experience, most regular 2T motors are OK on 5%. Most cutting out in the air problems are related to either tank position, or poor idle mixture setting. If you want a really reliable setup, then go 4T and fit an onboard Glo.

My inverted  setup NEVER misses a beat, starts immediately, idles so slow you can almost see the prop turning, and throttles beautifully.

Rob Cope26/09/2007 16:25:00
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94 forum posts

Thanks Timbo ,

You're a superb contributor to these forums - and right on the ball. You have given me great confidence in persevering with the running in. I seem to remember, now I'm responding, that short bursts (2 mins?) at full throttle with cool-down periods (5 mins?) in between are what's needed. So my 5 minutes idling at lunchtimes (and the engine) are not helping. I better get off down to the field in the early evening then.

Am I right in thinking the power of my .61 2-st should be similar to your recommendation of a 91 4-st? So the engine should fly the bird better than 30 degress climb? Even if she is whining a bit soprano-like the while...   All up weight is 7lb. I can't be more accurate because at this weight I have only the bathroom scales.  If it is the Sportsman Aviation 64, this gives a loading of around 23oz/sq' which, I understand, is a good region to be in.

Regards,

Rob

P.S. What is the origin (and literal meaning) of the 2T and 4T thing? I can't make out what the T is for...  

Tim Mackey26/09/2007 23:15:00
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20919 forum posts
304 photos
15 articles

Hi Rob. Fistly ( lastly on your list ) I am afraid I do not actually know where the terminolgy 2T and 4T originated, but it is quite common to use these abbreviations to describe a 2 stroke or 4 stroke motor. hopefully someone else will enlighten us !

Anyways....I always tend to run my engines in by fairly high speed running, with gradually increasing durations. Many engines prefer high revs, and higher temps in order to work efficiently, especially when no rings are fitted to the pistons, relying on the expansion due to temp to form a good compression seal. Donr be afraid to let it run fast, check what the recommended max RPM is and then choose a prop which will allow to get to that speed without having to work too hard, after it is nicely run in, a larger prop better suited to the airplane in question can be fitted. One thing most engines dont like at any stage, is labouring through having to turn a prop which is too big. Also, keep the mixture a bit rich for most of the running in, as this ensures sufficient oil is being dispersed to keep temperatures in check.

I actually prefer to keep my IC ( Internal Combustion ) I know THAT one - engines a bit rich all the time, as I despair at those peeps to have to insist on leaning out their poor little engines until they are screaming for mercy to within an inch of their lives!

7lb sounds a pretty good weight for 64" SPAN Spit. Mine is the Sportsman Aviation and is fitted with a 914T ( or FS if you prefer... ) and weighs just over 8.5lbs. Power is MORE than adequate, and I would never dream of going to a 120 in it. In fact a decent 80 would be fine, so at 7lb you are laughing. If your 61 is nicely loosened up, set up right ( mixture, fuel, and plug etc ) then it should perform better than you are finding at the moment. Mine will climb at approx 45 - 60 degrees easily and be out of sight at that angle too if I let it !

Flanker .27/09/2007 08:58:00
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622 forum posts
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Just to stir it a bit , it is worth considering which prop you are using too. It can make a huge difference to the way a model flies. Experimenting with glow plugs is worth it too. However changing many things at the same time is NOT a good idea. Follow Timbo's setting up tips until the engine will throttle reasonably well. Then try a new plug, always a good idea after running in. Then when you can get a flight without a cut, start to experiment with props. If you are running out of puff try reducing the pitch and see what happens. Try the same pitch and a smaller diameter too. Back to the plug thing. If a motor that runs well suddenly starts acting up try changing the plug before you fiddle. I STILL fall into this trap, I did it the other day, motor started well, throttled well, then cut on the strip at take off. Sounded like a rich cut , so I fiddled and got to run ok ish, but it WAS the plug, and I had to re set the mixture back to where it was when I fitted a new one. Good luck, oh and this nose over thing, I have an evil bipe that likes to nose over, the cure is to land with the nose up , balancing the drag with power, and land on all three wheels at once, (a three pointer ?) Takes practice but it works on this plane. Have fun. F
Rob Cope03/10/2007 01:01:00
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94 forum posts

Hi Guys,

Thanks once again for all the help. She (GP 61) has a Graupner 2-b 12x5 so might be lightly loaded at present, but then she may be running in. I might put a 3-b on there later if I can work out a good loading. From the spec of 2bhp @ 15k, I'd think that prop is small enough and 5" pitch should be steady as a rock.

My Irvine 53 (advertised as 1.3bhp) has a (something) 11.5x5 on there and flies beautifully, but only climbs out at 45 degrees, on a Boomerang 60 inch. To me the spit looks right/light in comparison. (12/11.5)^5 = 1.25 more power needed (less a bit for slight effective reduction in pitch) and the engine is 1.5 times as powerful, so I shouldn't be too far wrong - and even better... - that is unless the trainer should have a much smaller prop too!!! It is the prop I was sold with the engine and plane - and for running in - all new gear, so I would have though it should be right. My assumption however. Perhaps the proprieter doesn't like too much noise?

I also noticed some more vibration than I wanted on the spit. After the 10th dismantling of the prop/spinner for cowl removal, I noticed the Graupner and the spinner are both actually designed for a larger crankshaft diameter. I've made up a cardboard sleeve and the spinner and prop centre really nicely now. Yet to run it this weekend (to show friends.) I think the spinner came with a brass liner thingy... I'll dig it out. Is this a hint the propeller might be designed for a larger engine me thinks?

I'm running her in at present and I'll re-plumb and re-plug her to see if that's an improvement. Not this weekend as we have visitors and I can't squeeze in a shopping trip too. I have another 11.5x5 (spare for the boomerang) - perhaps I'll try that out on there. It can't be _worse_ can it? Thanks for the reminder Flanker

Oh I had a bump last weekend - yeah, flying in too slowly in a spit, engine cut _again_ and dropped it on a leg a bit hard. Cracked the mech retract leg mounting, but CA has lept to the rescue. I'll see how it holds up. Must be spares available somewhere...

Anyway, good luck all and I'll let you know how I get on. Is there a reference chart anywhere for recommended: engine type/capacity .vs. dia/pitch/blades somewhere? I see a Saito FA 30-S is rated at turning a 10x6 2-b which means It'll turn a 9x6 3-b. Now that sounds enormous for the capacity. I've read doubling a props total size (dia+pitch) means 32 times the power needed = scale^5. And more blades are a linear factor. I just found Flying Sites ( http://www.flyingsites.co.uk/howto/propchoice.htm ) and Prop Balancing ( http://www.uoguelph.ca/%7Eantoon/hobby/props.htm ) relating prop to engine capacity - and mine look OK.

Regards, Rob

Flanker .03/10/2007 08:26:00
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622 forum posts
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Well now Rob, I just got out the instructions for my Magnum .61 which is I believe more or less the same motor, although mine has a twin needlwe carby.

 For running in use a 12 x 6  after that you can go up to 12 x 7 or 13 x 5, I found on my bipe (heavy) that 12 x 6 seems to be great.  So you may have been a little under propped.

At what point does your motor like to cut ? ie when opening up after a slow phase, on tick over, or what, might shine a light .

From what I have read, three blade rs should be used for display purposes, as the more blades the less efficiant the prop is. They only use multiblades when there are ground clearance issues with the correct sise two blader .

For my two happny worth (based on experience!) if after some reasonable work on mixture/plumbing/ PLUG/ etc it still cuts, toss it out and buy a NEW Magnum, they are cheap and they work.  Fussy motors are model breakers. I spent ages trying to sort out an old Magnum 46 that I had had for twenty years, I did loads of damage to my plane due to cuts, and in the end the problem was due to wear on the crankshaft where it acts as a valve under the carb, due to the wear the amount of air in the crank case was changing due to heat expansion, ie a ground mix would be fine, but an air mix would be wrong. Took me ages to spot that one! But €80 on a new 'un sorted that. Did you say that your motor was "used" ?  Lets hope a new plug/plumb will sort the little blighter out ! 

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