extra slim Posted February 5 Share Posted February 5 OK all you experts out there. I can normally sort almost every eventuality on mine and most people engines, but this has got me stumped. Elderly OS 26 FS mounted at 7pm Inverted, on a newly built Atilla. Running OS F plug, Optifuel 4 stroke 20% nitro, tank sat on the floor of the fuselage, swinging a 10x4 prop. Top end, superb, idle, just pools up and dies, after about 10 seconds.. airbleed is screwed almost entirely out. Engine runs like a swiss watch on the test stand upright and will idle all day. I've even just tried a perry oscillating pump in an attempt not to pump, but to regulate the supply, but still the same. It does idle ok with the glow on, but I am so reluctant to use an onboard intelli-glo on this small aircraft. I assume the timing is OK due to its behavior on the test stand. It is elderly and hasnt got a load of compression and wont flick, and that is the only thing I can think of, that it might need a new ring, and that extra comp, may help it bump along at idle.... Answers on a post card. Failing that, can anyone recommend an inverted 26 FS or 30 FS setup.. The OS, and Saito are both airbleed, with SC and ASP twin needle. I am tempted with a saito 30, but would be miffed if I experienced the same having shelled out.. Last resort would be to re-butcher it into sidewinder.. Ponder, ponder!! Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted February 5 Share Posted February 5 (edited) Keep it simple as a very wise old engineer one advised me.............is the airbleed actually bleeding? Edit. sorry just rerread your post and the motor runs ok on the test stand.........hmmmm fuel level? Where's Jon when when we need him? Edited February 5 by Cuban8 Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 Top of the tank is a smidge (5mm) above the centre of the carb, the rest is below.. 4 oz square SLEC tank. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 5 Share Posted February 5 (edited) 1 hour ago, extra slim said: Failing that, can anyone recommend an inverted 26 FS or 30 FS setup.. The OS, and Saito are both airbleed, with SC and ASP twin needle. I am tempted with a saito 30, but would be miffed if I experienced the same having shelled out.. Last resort would be to re-butcher it into sidewinder.. I fly successfully on your set up Extra Slim, although on a 9 x 5 prop. it has to be fuel flow, as you summise, but you have to have half the idle screw hole covered by screwing in. and you won't like this, although all new, you have a fuel pipe pressure leak, or a tank pressure leak, or the clunk sticking at the back of the tank. The 4oz tank has a very short clunk pipe, than can wander high in the tank, or get stuck. go over each joint and every inch of the tank under water with soap bubbles blow every pipe, blocking the others in turn. You have a pressure leak I feel. Edited February 5 by Denis Watkins 1 Quote Link to comment Share on other sites More sharing options...
kc Posted February 5 Share Posted February 5 (edited) SLEC square tanks are unusual in that they have extra holes you can pierce for a fuel gauge, two others for filling /vent and also a rubber washer around the outlet pipe, all could be the fault. Also if reusing an old previously crashed tank it could have a leak around the two plastic parts. Edited February 5 by kc Quote Link to comment Share on other sites More sharing options...
John Wagg Posted February 5 Share Posted February 5 Have you tried a different plug. My situation the engine would run with the glow connected but not without at idle. Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 Thanks for chipping in chaps. I did pressure test the tank under warm water, and it was fine. I usually find that if a tank does have a pressure leak somewhere, the idle goes lean, as opposed to rich. I will of course, remove the full setup and put that on the bench, bypassing the use of the test bed tank. And Denis, yours is inverted right? Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 1 minute ago, John Wagg said: Have you tried a different plug. My situation the engine would run with the glow connected but not without at idle. It is a brand new OS F which I usually swear by. And my situation is the same as yours.. Just too rich at the bottom end, even with the low speed screw wound way out. Quote Link to comment Share on other sites More sharing options...
Jonathan M Posted February 5 Share Posted February 5 Would it be worth revisiting your conversation with Didier here: Ohmen Inverted OS26 FS with NO pressure feed from tank...? Quote Link to comment Share on other sites More sharing options...
Jon H Posted February 5 Share Posted February 5 I suspect you are outside of the tuning range of the engine with that fuel. Change the fuel as 20% nitro will not be helping you at all. The high nitro fuel will require the main needle to be opened further to correct the mixture. Its likely you are simply beyond the adjustment range of the air bleed screw and the engine is just drowning. It wont manifest when upright as the fuel is able to drip out of the carb but inverted it just floods the intake. The excess of fuel will also over cool the engine at idle causing a flameout. The high nitro might also be leading to the engine running excessively rich and this will make things worse as well. The OS blurb suggests a 5% nitro and 15% nitro blend, each with 20% castor 🤢 I would reset the airbleed to half open, tip some 5% nitro 15% synth oil fuel into it and give that a go. it will raise the engine's operating temperature and bring the thing back into its tuning window. I have not tried it inverted admittedly, but my FS26 is very happy on this brew as is the battered old fs40 i rebuilt some time ago. that little 40 gets absolutely thrashed in my seagull challenger and is quite happy with all of my abuse. 1 Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 8 minutes ago, Jon - Laser Engines said: I suspect you are outside of the tuning range of the engine with that fuel. Change the fuel as 20% nitro will not be helping you at all. Good shout Jon I'll give it a whirl.. Thank you Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 5 Share Posted February 5 31 minutes ago, extra slim said: Denis, yours is inverted right? Yes, inverted I fly the 26, and the Saito 30 and 40, inverted And like you, the tank has to be rock bottom, On floor of the model And with each, plumbing has to be spot on, and I fly all three on 5% nitro 1 Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 excellent, I have a couple of things to try/check.. lower nitro and re check plumbing.. Thanks all Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted February 5 Share Posted February 5 You might want to ask a moderator to change the thread title, to aid future searches 🙂 Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 5 Author Share Posted February 5 Oh yeah, missed that.. I’m very invested in this little inverted monster!! 1 Quote Link to comment Share on other sites More sharing options...
David Davis Posted February 6 Share Posted February 6 I don't know whether this is of any help or relevance but I'd always run my Japanese and Chinese four-strokes on fuel containing 10-15% nitro and 15% oil. I had another mix, 5% nitro and 15% oil, for my old Lasers and what two strokes I continue to run. One day I arrived at the flying field having left the high nitro fuel behind. So I filled the tank with the 5% stuff. The engine started and ran perfectly. I did the same trick yesterday with my Thunder Tiger 54. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted February 6 Share Posted February 6 If the engine could use a new ring, its probably worth doing that fix anyway. On the % nitro question, I can only say that I have several OS 4 strokes that run perfectly on 5%. 1 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 6 Share Posted February 6 (edited) Only change one thing at a time. As already said go to a lower nitro fuel first and go as weak as you can on main needle for max performance at full throttle then read adjust air bleed idle mix if neede .If poor idle persists sort out poor compression as this will cause poor combustion and poor idle. Valve clearance or carboned up valves and ports all contribute to poor compression and running .Also check bearings for rock especially the rear bearing . Hold prop and try to rock it back and forth. Any movement will indicate a worn bearing that wil affect the valve timing causing poor idle and a slight loss at top end. Always change both bearings. I belive that most , if not all FS 26 engines had bronze bushes for cam bearings and they are unlikely to be worn. One other thing to check first . Make sure it has the correct main needle. A friend bought a nearly new looking OS 26 FS at Wings and Wheels a while back for £30 . It had good comp and felt like nearly new. It would run flat out but not idle and needle had to be screwed right in for it to run atall. It turned out to be a defective needle valve and the actual needle had been pushed out through the brass part. Simple test put a piece of fuel tubing on fuel nipple and blow through it while screwing in N V . It should shut off completely. If it doesnt fit another NV. Dont give up it can be sorted but decent compression is vital. Edited February 6 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Nigel R Posted February 6 Share Posted February 6 12 minutes ago, Engine Doctor said: Valve clearance Good point, and easy to check. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 6 Share Posted February 6 Look at GC piston rings here if you decide to fit one . His product are excellent and fairly priced .https://gcpistonrings.com/ Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 6 Author Share Posted February 6 Excellent feedback guys. When I acquired it, I got a new ring from Gavin as I thought it was worn and getting one in the future may be tricky but I didn’t fit it, as it was fine, upright!. Valve clearances etc checked. I’ll try lower nitro, check NV is the correct one, and then fit the new ring.. I’ll get there Quote Link to comment Share on other sites More sharing options...
Richard Acland Posted February 6 Share Posted February 6 (edited) Just one last thing, how old is thefuel you are using. I had engine problem last year with an inverted four stroke.My fuel had overwintered in my garage. Someone suggested getting fresh fuel which I did and it solved the problem. Edited February 6 by Richard Acland Spelling Quote Link to comment Share on other sites More sharing options...
Maurice Dyer Posted February 9 Share Posted February 9 Jon is right. Lower nitro, and close that air bleed. 10% nitro MAX. Maury Quote Link to comment Share on other sites More sharing options...
Rod Parsons 1 Posted February 9 Share Posted February 9 Hello I would also add that if the glow plug is new, is it a fake? Quote Link to comment Share on other sites More sharing options...
extra slim Posted February 9 Author Share Posted February 9 Hi All So, I tried some lower nitro fuel, only had 10% and slightly improved but still not acceptable. So.. I removed the engine from the airframe and stuck it on a test bed. Before running, I checked the clearances and they were towards the loose end of the scale (0.04-0.1), so nipped them up and noticed a little improvement in compression. Fudged my test bed, and mounted it inverted, with the tank (not the one in the ariframe), in the same position as that on the model.. And it is now fine. slightly high, but perfectly doable. I think the combination of lower nitro, slightly increased compression and a new tank have got me to a satisfactory position. So, the engine will be reinstalled into the airframe, run under the same conditions. If any issues then the tank will be removed, checked and swapped if necessary... getting there IMG_1912.MOV 2 Quote Link to comment Share on other sites More sharing options...
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