dlonrar Posted November 23, 2015 Share Posted November 23, 2015 I have an SC46 running 10% nitro fuel using an OS 8 plug, the engine runs ok with no problems during warm or hot weather (apart from the usual top needle adjustments). Flying in cold weather, the engine is ok on startup,idle, max revs and take off, but after a while during flight the engine revs surge (drop and pick up) without changing throttle position. Eventually the engine revs drop to idle or a dead stick occurs. Note, I have not changed the top or bottom needle settings since the plane last flew in warm weather, about 3 weeks ago. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted November 23, 2015 Share Posted November 23, 2015 I wonder if you are getting some icing on/in the carb due to the cold wet air? Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted November 23, 2015 Share Posted November 23, 2015 hello dlonar..you probably stated yourself...... the problem...you haven't changed the needle settings since the warmer weather...i bet it needs opening a couple of clicks on the top needle......to compensate for the colder temps(richen it up slightly) ....give it a go and report back. ken nanderson..ne..1 reporting back dept. Edited By ken anderson. on 23/11/2015 17:09:58 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted November 23, 2015 Share Posted November 23, 2015 I would go with Kens suggestion.....cold air is more dense so you are effectively getting more molecules of air into the cylinder....for the same number of molecules of liquid fuel you then have a weak mixture (assuming it was perfect before...). If the engine is lean it may then be overheating slightly which would give rise to the uneven running & eventual cut out. Richen the mixture slightly & see if that helps...... Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted November 23, 2015 Share Posted November 23, 2015 notice i've changed my name in the post above.... ,,, ken anderson...ne...1...... who am i dept?. Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 23, 2015 Share Posted November 23, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Spice Cat Posted November 23, 2015 Share Posted November 23, 2015 Posted by Percy Verance on 23/11/2015 17:56:28: Is that one of them there nom de plum things ken? Is that French for 'I've lost me plums' ?? Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted November 24, 2015 Share Posted November 24, 2015 Posted by Percy Verance on 23/11/2015 17:56:28: Is that one of them there nom de plum things ken? ...................................................................................................................................................................... no its a passed your sell by date.................i have to buy a newspaper to find out what day it is..............i got a new phone a few weeks ago and received a msg from a number who i didn't recognize.......i replied back without my glasses on and when i read the msg later i had put -who ate you...instead of who are you? sorry for going off topic ... ken anderson...ne...1........ who ate you dept. Quote Link to comment Share on other sites More sharing options...
flytilbroke Posted November 24, 2015 Share Posted November 24, 2015 Ken's suggestion cures most of the engines given the same circumstance. Brownie points Bob Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted November 24, 2015 Share Posted November 24, 2015 well done FTB(bob)..hope you are well...your name has been added to my list of benefactors...for when i win the lottery million's.... ken anderson......ne...1.... lottery millionaire to be dept. Quote Link to comment Share on other sites More sharing options...
dlonrar Posted November 24, 2015 Author Share Posted November 24, 2015 Thanks all for the entertaining and informative posts. I will try Ken's suggestion when the next spell of cold flying weather is around. Luckily I only live 5 mins away for the flying site. Quote Link to comment Share on other sites More sharing options...
dlonrar Posted December 15, 2015 Author Share Posted December 15, 2015 ok ken, Flew today. Conditions low wind, vis 800m , low cloud 400 feet, mist. Flew aircraft today, air temperature not as low as previous (problem) flight. No adjustments to needle settings. After take-off engine showed ‘surging’ problem, throttled engine back to half throttle, engine ok. After 4mins of circuit flying, rolls ok. Did loops after 6 mins and plane lost power as approached top of loop, decreased throttle to half and engine speed back to normal. Then went to full throttle ok. Landed plane ok. Allowed engine to cool and adjusted top needle as instructed, engine started ok. However, plane nearly died on take-off. Made it into the air safely. Loops this time had no loss of power, rolls ok. Did a few landings and take-offs ok. After third landing restrained plane and did standing engine rev test prior to take off, engine died. Hand tested engine temperature did not seem overly hot. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted December 15, 2015 Share Posted December 15, 2015 I would say that your first flight showed classic overheating symptoms. Did you richen the mixture or lean it though - and did you do a nose up test before each flight? I wouldn't have let the engine cool before making the adjustments though - that needs to be done at running temperature... Edited By Martin Harris on 15/12/2015 19:00:19 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted December 15, 2015 Share Posted December 15, 2015 The intermittent nature of the problems you are experiencing makes me wonder if there might be a foreign object in the carb or suchlike.... Is it a rear needle set up? If so it might be worth removing the blanking plug from the carb & having a look in there.....I once found a grass seed in the carb of an engine that was misbehaving....how it got there Lord alone knows but the engine would run fine until the seed blocked the jet into the carb!!! Quote Link to comment Share on other sites More sharing options...
Tony H Posted December 15, 2015 Share Posted December 15, 2015 It might be worth trying a slightly hotter glow plug and richening the high speed mixture needle a couple of clicks more than your warm weather setting. Also make sure the fuel tank clunk isn't getting stuck, check the fuel tank plumbing has no holes/splits in it and the fuel filter has no foreign objects in it and is done up tight (if you have one fitted). Tony H Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted December 16, 2015 Share Posted December 16, 2015 hello again dlonrar...if you are happy that the plumbing is 100% ok....it still sounds as though the engine needs tuning via the needles.......when its hot and running.one click at a time and see/hear the result...check that its not over-propped and check what steve mentions...a bit of rubbish stuck in the carb needle seat...and maybe swap the plug/fuel...try a friends fuel?Forgot to mention do all the tuning with a 3/4 tank of fuel....not full. ken anderson...ne....1 tuning dept. Edited By ken anderson. on 16/12/2015 09:51:48 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted December 16, 2015 Share Posted December 16, 2015 It does sound as though you engine is going weak on take off and when at the top of a loop .Tune top end needle to Max power then turn back two or three clicks to richen the mixture. If problem persists then check the tank plumbing. How old is the plane/tank ? And are you using brass tubing? If its more than a year old and you are using brass tubes then its possible that there is a pin hole in the supply tube where it goes through the rubber bung. You say you are using 10% nitro fuel . Nitromethane attacks and dissolves the copper content in the brass tubes and t!he cheap Chinese brass tubeing fails very quickly with higher nitro fuel. Replace with ally pipe of same size to cure future problems. There are of course other problems that could cause these symptoms but try these to eliminate a couple of basic problems. Good luck and let us know the outcome . Quote Link to comment Share on other sites More sharing options...
Keith Berriman Posted December 16, 2015 Share Posted December 16, 2015 I would also suggest after tweaking as suggested above can you do a full throttle nose up on the ground test ?? Quote Link to comment Share on other sites More sharing options...
J D 8 Posted December 16, 2015 Share Posted December 16, 2015 Had an Enya 40 on a Limbo dancer with much the same problem,ran fine in all conditions except when the temp got close to zero. Tried most of the fixes above but in the end a strip of cloth tied around the base of the cylinder and a good run up before take sorted it. It just wanted its winter woolies on. Quote Link to comment Share on other sites More sharing options...
dlonrar Posted December 16, 2015 Author Share Posted December 16, 2015 OK, thanks for all the suggestions. I have a lot to try, most of the suggestions I have tried before and I am thinking about scrapping the plane and engine. The problem only arises in cold weather. Currently the engine as had the top needle riched up from the summer settings. If I fly with the same settings the following day and its warmer everything is ok, maybe not perfect but there is no loss of power or surging. Suggestions so far, will have to revisit these: Grass seed, doubt this as I fly the plane off a tarmac strip. Tank, engine, fuel lead problems, air leaks – possibly not. As I changed the engine, fuel lines and tank last winter when I had the same problem. I was then using a SC 46 with a 11*6 prop and 5% nitro and it had the same problems in cold weather. I changed the tank (seagull standard – no brass fittings), fuel lines and ran in a new SC 46 with 11*6 prop using 5% nitro. Still the same problem, I changed to 10% nitro and the problem cleared. Or, had the weather got warmer? I think the latter, as this is the combination I flew through from Easter to the present day. I like the muffler idea, but how does this fit the engine getting hot and leaning off ? Hotter glow plug, possible, But does this go against the riching of the mixture ? Clunk position, possibly not as the problem can occur when flying level circuits with varying power. Is it a bottom needle problem? As the power loss is recovered by going below half throttle. As I understand it, the transition from bottom to top needle fuel flow is mid throttle ! Out of all the suggestions, I think I’ll stick with the top needle settings and post start up engine checks. Quote Link to comment Share on other sites More sharing options...
Stevem3akm Posted December 16, 2015 Share Posted December 16, 2015 Hi, just a thought, but try either a finer pitch prop or a smaller diameter prop(10x6/7). The current prop may be loading up in what could be slightly denser air causing it to overheat gradually. I had this problem years ago and the props cured it for me. Regards Steve. Quote Link to comment Share on other sites More sharing options...
PatMc Posted December 16, 2015 Share Posted December 16, 2015 Posted by dlonrar on 16/12/2015 17:38:55: The problem only arises in cold weather. Currently the engine as had the top needle riched up from the summer settings. Running richer will cause it to run cooler. IMO It's most likely to be an intermittent blockage in the pipework/carb or a pinhole in the feed pipe. Messing about with existing good carb settings is a good way to learn about deadstick landings. There's never any need to change them summer to winter (UK), unless the type of fuel is changed. If cars came with user adjustable carbs or injectors the AA, RAC & other breakdown companies would be the biggest industry in the UK & the roads would be littered with abandoned vehicles. Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 16, 2015 Share Posted December 16, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
dlonrar Posted December 27, 2015 Author Share Posted December 27, 2015 Flew plane today (cold with 6mph wind), after some of the following 'adjustments' in the hanger. 1. Noticed barrel of exhaust was leaking waste oil from joint, so lined joint with aluminium tape, re-fittened and tightened. 2. Flushed out carb with fuel. 3. Shortened fuel pipe between rear needle and carb. 4 Flushed out with fuel the top needle valve fitting with needle removed (done by pressurising the fuel tank when it was full of fuel). and At field: 1. Started engine , ran at tick-over for 1 min. 2 Set full throttle and leaned off to max revs. Riched up TNV and tested the nose up (engine leaned off but did not stop) 3 During the flight had none of the engine problems mentioned above in earlier postings, loops and rolls ok. Next check on the settings is a very cold (close to zero) windy (above 15mph day. Thanks all above for the suggestions and tips. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted December 27, 2015 Share Posted December 27, 2015 well done..thanks for the feed back--you mention it leaned out when you held the nose up-i would have opened it 1-2 clicks... ken anderson...ne.....1 ......nose up dept. Quote Link to comment Share on other sites More sharing options...
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