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The finer points of two stroke tuning

What are the likely causes of a slightly hesitant pick up ...

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Bob Moore24/01/2011 15:37:47
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Hi all
 
I've just been re-tuning my new Irvine 40 2 stroke (after a couple of dead sticks the last of which resulted in a damaged fusi.) This is twice in a row I have had damage from low level dead sticks. (I usually manage to land well enough from high level ones.)
 
I guess the engine had 5 or 6 tanks through it now.
 
OK, I have a really nice tickover and have tuned the top end and richended a click or two, but from mid revs to full throttle there was a slight hesitation. I have (reluctantly )opened the slow running screw by about 1/8 of a turn and it seems to have improved it. Was this the right course of action?
 
With the nose held high the pick up at all speeds seems to be ok.
 
I'm hoping my dead sticks were from running too rich, plus a bit lean on the slow running needle?
 
Am I right in thinking a pinch test should have the same effect at all speed ranges, ie top, mid and slow?
 
I hear a lot from club members that they have engines that run well on the ground but die in the air, and I don't want to have to repair this again!
ken anderson.24/01/2011 17:34:56
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bob-make sure you're not tuning the top end needle with a full tank of fuel...if you are..the norm is for the engine to lose that tune when it's used about 1/3 of the tank of fuel.....and when you alter the bottom needle-you need to alter the top one as well.....and finally the cold temp's we are having dont help when trying to set up our 2st engines
 
 
ken anderson ne...1.
flytilbroke24/01/2011 17:40:04
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Keep it rich enough to stay running, You have not had enough running time on it to worry about fine tuning. Hesitation usually means slightly lean on the low end. Some engines will always have that hesitation if the throttle is opened quickly although this should not be too evident on a well run in engine.
Bob Moore24/01/2011 18:51:01
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Thanks Ken. Funnily enough, the thought of tank level came to me after I'd posted. I wondered about different pressure at different levels. The tank was full, at least when I started. I suppose half tank tuning is best idea then?
 
I did know that altering the bottom end affects the top end tune.
 
I did make a point of holding the nose high for a good few seconds when testing as well.
 
Thanks Flytilbroke as well. I think I'm getting there slowly. Some engines seem to tune quite easily, but I guess maybe not so with some new engines?
Myron Beaumont24/01/2011 19:42:02
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I have to slightly disagree about tank levels when pressurised .I always hold the A/c vertically for about 10 seconds to make sure of no alteration in revs .Of course ,this is always performed pre-take off with a fullish tank the level of which can be several inches below the carb. When vertical,set the engine slightly richer than the perfect run/revs.No problem!
stu knowles24/01/2011 20:52:13
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You have posed a question that will get you a different answer for every person you ask although you have also correctly identified probably the biggest model breaker in model flying, engine cuts!
 
This is my way and (touch wood) I rarely suffer from this problem.
 
Tune for high speed. leave it no more than a couple of click on the rich side of perfect.
Tune the low speed,Read up how to do airbleed and two needle carbs. Get the right setting by pinching shut the fuel feed just before the carb while the engine is ticking over.
 
If the rpm rises a lot, its too rich. if they die with no rise, too lean. small rise in rpm and then slowly dies.... just right (said Goldilocks)
 
If the engine still plays up, clean the carb and back flush with fuel. Use a good plug, My favourite is an Enya No 3.
 
Good quality engines repay the investment times over by not wrecking models.
 
Time invested in getting a good engine set up is rarely wasted. Good luck
stu k
Bob Moore25/01/2011 11:02:53
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Very interesting stuff guys. Thanks.
 
I just had another little tuning session. I undid yesterdays richening the low speed needle having read that hesitation in pickup can be caused by a too rich setting. And my logic says , if anything, Irvine would 'factory set' slightly rich as well.
 
I must say in the past I have never held the nose high for longish periods and opened and closed the throttle. It makes obvious good sense.
 
The low speed I think is right, when I pinch to stop, there is a slight pick up in speed before the engine dies. High speed seems more difficult to tune. It runs fast and when I lean it out it does reach a point where it wants to die, but I can't really say there's a point from very rich to just right where it picks up. There's a more obvious point where it's too rich after a few clicks out. And there's no obvious pick up with the pinch test at high speed?
 
It will pick up nicely after slow running (or ticking over) for a good few seconds (as you would in a slow low pass) though if you really over do it and wham the throttle flat out you can get it to die. I guess that will happen pretty much with any engine? Pickup from mid revs to flat out with nose high is good.
 
I think it's about the best I can do anyway. I'll see how it goes next time we get a decent day, and try to make sure I stay high while I play with slow running and picking up.
 
PS I guess by air bleed setting you mean the method of attaching a fuel pipe, blowing through it and setting up that way initially? I've done it with e bay engines that I don't know the initial settings of, but didn't bother with this new one that had recommended factory settings.

Edited By Bob Moore on 25/01/2011 11:05:52

Steve Hargreaves - Moderator25/01/2011 11:35:52
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Good advise there & just to echo what Stu says.....it is very worthwhile spending a bit of time getting the motor set up....ask for some help off the guys who just turn up & fly.....the "experts" who spend all the time fiddling with their engines are best avoided... Once set up a motor shouldn't need adjusting unless you change the fuel, plug or prop or the weather changes dramatically & even then a few clicks will usually suffice!!!
 
If it's a new engine then it might be worth checking backplate, head & carb screws for tightness......you don't need to lean on them really hard, a light nip is usually sufficient....(apologies for the use of technical jargon there.......).
 
Also as Ken says allow the engine to warm up fully before tuning......around 1/4 throttle for 2-3mins is usually enough but with the very cold weather maybe a bit longer....the number of people who start an engine & then immediately run it up to full throttle/revs before the engine has warmed & stabilised.........!! Makes me shudder.......
Steve Hargreaves - Moderator25/01/2011 11:46:04
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Bob, it sounds about there for a new-ish motor.....get a few more flights under its belt & then perhaps retune it........
 
I really is important to get the main needle set right first as this dictates how much fuel will flow into the engine...the master control if you like....the idle needle only affects the low end but is in turn affected by the main needle.
 
The reference to an "air bleed setting" refers to a simpler carb whereby the idle mixture was adjusted by an air bleed screw.....rarely seen these days apart from on smaller engines.....
 
Incidentally what prop, fuel & plug are you using??
Bob Moore25/01/2011 12:37:47
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Prop is a 10 x 7 apc. I have an 11 x 6 I was thinking of experimenting with. More thrust, lower speed is it? Both are as recomended sizes by Irvine. Mind you it will climb vertically with the 10 x 7, bit on the fast side for my flying though.
 
Fuel is Model Technics GX10.
 
And I go by my dealers recommendations for plug (Stan Yeo. He has been flying for years and used to write for RC mags.) I think it's Taylors, (Long reach?) with an idle bar.
 
PS It seems to run and sound great, it's hard to think it will let me down, but one never knows?  Some engines seem  to have minds of their own once in the air!

Edited By Bob Moore on 25/01/2011 12:39:14

Steve Hargreaves - Moderator25/01/2011 15:42:24
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Prop sounds fine....either would be good for a 40 in a sport model.....as you say an 11x6 might give a bit more thrust at low speed but I doubt there'd be much in it!!!
 
Interesting choice of fuel & plug.....both were very commonly used in the 70s & 80s!!!! Nothing wrong with either an idle bar plug or GX 10 fuel but they have been around for donkeys years....the GX range was introduced by Model Technics during a global shortage of nitromethane in the late 70s (yes really) & used a "substitute" compound....
 
Much as I respect Stan Yeo I wonder if a more modern fuel might be worth trying & perhaps lose the idlebar too....these can tend to shield the element a bit & in my experience simply aren't necessary in a modern engine.....Taylor do a "standard" non-idlebar plug & these are excellent (cheap too!!)
 
Could you cadge a tank or two of a more modern fuel mix off a clubmate & see how you get on with that??
Bob Moore25/01/2011 15:49:50
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Interesting stuff. The fuel and plug combi seems to work ok for me, but what other fuels would you recommend? Always worth trying something else. I've got other plugs, (without idle bar) I might give one a try.
Lee Smalley25/01/2011 16:31:29
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idle bar plugs just are not needed in std engines any more, and as for gx 10 well nothing is wrong with it ......its just more expensive than straight or 5% and for no reason.
 
5% fuel and a std taylor plug will run an irvine 40 fine 11x6 or 10x7 is ok as well, its just down to tuning
Lee Smalley25/01/2011 16:35:34
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many many moons ago when i was just starting out i was told by a wise old head if you want to know about engines and how to sort them find the guy who just turns up and starts his engine, he does not mess around with needles tweeking every last rpm from his engine he starts up and flies no deadsticks no disasters ! find him and bribe him to show you how !!
Bob Moore25/01/2011 16:55:06
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find him and bribe him to show you how
 
where does he live or which club does he fly at ?
Steve Hargreaves - Moderator26/01/2011 09:52:35
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Lees point about asking the right guy to help set yer motor is a good one...I alluded to the same point in my first post. Most clubs do have them but they are usually less vocal than the other type of "expert" who will wind your NVA around a few times.....have loads of deadsticks & then declare your motor to be rubbish!!!!
 
But I digress.....
 
Bob it is a brave man indeed who puts his head above the parapet & "recommends" a fuel......as mentioned previously there is nothing wrong with GX10....its been around for Donkeys years.....but that doesn't mean that "better" fuels aren't available....technology advances....fuels, & particularly oils improve. After all you wouldn't go putting a mineral 20W50 oil in yer nice new shiny Ford Mondeo now would you???
 
Personally I use the Southern Modelcraft Mo Glow stuff...5 or 10% nitro. This has 15% synthetic oil & 2% castor. Only real drawback is that you can only buy it at the shows. I've used it for years....my engines (2 & 4 stroke) run & last well on it & its cheap.....what's not to like!!! I suppose the best fuel is one you can get hold of easily.......
 
Some interesting fuel related stuff here & on a "sticky" in the IC engines section of the Forum.....
 
Fuel it seems is a topic that produces lots of debate..... Ask 10 modellers for their opinion about fuel & you'll probably get 11 answers. My view would be find a fuel that works well in your set up, you can get hold of easily & stick to it!!!!
Lee Smalley26/01/2011 12:35:55
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i have used soooo many types of fuel over the years and i have yet to find a rubbish one !
they are all good in my opinion
i use weston 5%nitro liquid gold now as i can get it sent to me in the post and its cheaper buying 4 gallons at a time than over the counter, i don't use castor any more but i don't half miss the smell
Bob Moore26/01/2011 22:57:58
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Ah well, did another tune this morning richened the main needle 4 or 5 clicks and the high speed pinch test worked this time. I had it a bit too lean. One more start to check again. engine started but the glow clip was wobbling and looked like it was about to fall into engine running at half throttle. made a grab for it and stuck my thumb in the prop (as you may have seen in the 'how stupid am I' thread. Hence sat in hosptal bed in Torquay having had theatre surgery to put half my thumb back. touch wood seems ok. 1st night ever in a hospital! @ age 63. not bad. all my ic models will now have remote glow points soon!
Lee Smalley27/01/2011 10:44:16
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Bob i use a cloths peg type connector (i think mine was a thunder tigre one) for my glow connection and it does not wobble in anyway or sort, its not suitable for every installation but most !!!
Lee Smalley27/01/2011 10:46:54
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