Should I just give up on this engine and chuck it in the bin?

[Bob Moore]

I don't seem to have a lot of luck with IC engines? Tuning a new Irving 40 a couple of years ago I ended up with 4 days in hospital when I tried to stop a fast revving prop with my thumb. (You may remember the gory pictures I posted.)

Anyhow, at some expense I electrified my Wot 4 and it's a joy, but I still have a couple of IC models around and having got my nerve back with IC and even flown the odd one (and improved my working practices) I've been running up and SC40 that I recently fitted to my Frankenstein model I mentioned in another thread.

Compression is reasonable.

I have done the usual stuff as a basic set up. Like close throttle to almost closed and blow thru a tube to set up low end and the top end just experimented a bit. New idle bar plug. (I've tried others.) But fuel a couple of years old I guess. The other day I had it running beautifully after an hours fiddling about. Nice tickover, good pick up, good top end.

So I went out today to test it again and it is misbehaving again. It runs for a while, will tick over nicely, pick up, rev up, then randomly it dies (usually low revs.) I screw the throttle screw in an 1/8, I screw it out an 1/8, I try the main needle in a click or two , out a click or two and so on, and so on. It's driving me nuts. No dirt in fuel. I've had the tank out. Clean. Blew the carb thru, nothing blatantly obvious. No leaks around the carb or back plate. It just won't play ball?

Could it be the fuel is just too old? Am I wasting my time? Should I buy some new fuel? Someone told me it should still be ok, was kept in the cool and in the dark.

I must admit my suspicion is being drawn to the fuel as I have also tried Frankenstein with an old , previously reliable , SC 25 and that proved a pig to get running properly.

I'm getting half tempted to put the still almost new Irving on Frankie, but fear I may still encounter problems if there's a problem I'm missing here?

Any suggestions welcome please

Edited By Bob Moore on 06/09/2012 17:02:28

[kc]

It might well be the fit of the needle valve in it's housing, maybe another needle valve might be worth trying. But first try a few turns of PTFE tape ( plumbing stuff ) around the threads which might improve the seal.

Also replace the fuel pipes including the clunk tube, ensure it's not too long and hitting the back of the tank.

Borrow a tank full of fuel from a clubmate!

[The Wright Stuff]

Hi Bob,

I have to say that I would definitely try new fuel, maybe with 10% nitro to reduce the needle sensitivity... I had a similar problem a few years ago that was solved instantly by using new fuel.

I have heard people on forums strongly disagree with this, and claim that fuel does not go off. Perhaps that is true for some fuels, or in some situations. But storage light levels, temperatures, the degree to which the container is airtight etc etc all vary from person to person and could all have an effect. I keep my fuel container in a black bin bag in a cool place, with the lid tightly fastened.

Got to be worth a try...

[Bob Moore]

Thanks for the replies. I've been out and tried it again now it's cooled down again and still no joy. Started easily, ran , stopped, started easily, revs, tickover, picks up well, stops randomly.

I should have added in my first post, when it stops there's still fuel in the feed tube to the carb. The engine is mounted canted 90 degs so the tube is on top and very visible. No air bubbles either.

After it has stopped it restarts first flip with an electric starter so there appears to be fuel in the engine too?

Fuel is Model Technics Expert Mix GX10. I should get into the habit of writing the date purchased in marker pen on the container? THis may well be at least 2 years old?

I think next stop will be to try some new fuel.

Edited By Bob Moore on 06/09/2012 17:28:29

[The Wright Stuff]

No worries, and good luck. I know from bitter experience just how frustrating these problems can be.

[Reno Racer]

Is the plug too cold?

I would try higher nitro new fuel and if thst doesn't work try a hotter glow plug

I've had similar problems before, fuel overly rich which then wetted a glow plg that was too cold.

[Bob Moore]

Petrol certainly goes off if left in a can, even a sealed can. It even smells different.

It certainly is frustrating though. I go to my strip and see people flying IC without problems mostly (though there is the odd dead stick) . Havings said that, a lot of them fly more often than I do so engines get used more and I suspect fuel is more fresh. I do other stuff, paraglide, mountain bike, kayak etc., so get to the strip less often.

I will report back if it solves the issue.

[Reno Racer]

I have found with the right fuel, glow plug and prop you hit that 'sweat spot' with an IC engine. My ASP 91 FS runs without fault, has never dead sticked on me, never needs adjusting and starts up after a few flicks. It still hits 10500 rpm on a 14 x6 MA prop on 15% nitro, even with after a move from flying it in the heat of Oklahoma to the slightly damper northen Germany.

Similarly, it has taken me ages to get my old Saito FA65 running nicely without stopping after a couple of minutes of running. Not helped by an inverted setup (although the ASP 91FS is inverted in my Corsair). A hotter plug solved the Saito's refusal to run properly.

[Bob Moore]

I must admit I've never got into changing plugs, though it's a good idea.

I'm inclined to try fuel first because I can almost hear it faltering at some speeds when running and there was an inordinate amount of oil on the ground when I ran it up for a while, even though it wasn't running rich.

My sc25 was as good as gold. Never let me down and started with a flick of the finger, so I know they can be good (sometimes.)

[richard cohen]

all of the above are worth looking and even small airleaks can play havoc with running. With regard to sealing the needle valve, with nothing against KC, rather than use PTFE tape (which can pull into thin stringy bits ) i pick some fuel tube with a tight fit into the needle housing and an inside diameter tight around needle threads and cut a thin slice of fuel tube to make an o ring.fit it to needle, ease it into housing and it forms an airtight seal backing up the original needle seal.

Rich

[Rusty C]

I just got my Irvine 40 running well today, It was reluctant to idle for any good length of time. The motor was 2 tanks old a still would not idle. It turned out that good run in process, a slight lean of the low end and a hot plug was just what the doctor ordered.

Try not to lose the faith Bob, it just takes some time, I was hopeless way back with my cars, But now I can hear whats wrong, You will get it sorted soon

Thats a good point about the prop selection Christian

Rusty

[Bob Moore]

Don't ever listen to people when they say fuel doesn't go off! Went to the field today and after a couple of flights with the leccy Wot 4, scrounged a tank of fuel from the only other guy there, for the SC40.

It ran like a dream. Didn't even have to change any carb settings apart from bringing the tick over right down. All my wasted time, effort and frustrations with this engine and I was on a loser from the beginning because of the fuel. The stuff I scrounged was expensive stuff, Pro Synth 2000 (10%) from Weston UK., but I'm fairly convinced it would run ok if I got some new of my usual stuff.

Back to the leccy thing though. I now have 3 LiPOs and made the mistake of putting one I 'd used back in for a second flight. Took off ok but my Wot will usually climb vertically pretty much with a fresh battery, however when I tried it, it fell out of the sky. (Not literally.) I Climbed and stalled and fell. I landed quickly and checked the voltages. Dooh! I'll be more careful next time.

Thanks again guys for the advice on my troublesome SC .

[The Wright Stuff]

Excellent news!

I'm glad that I'm not the only one who's found this. Fuel (or at least some types of fuel) DOES go off!

Pass it on!

[Martin Harris - Moderator]

I have to admit to being in the "sealed containers of fuel don't go off" camp despite your findings, Bob. Have you tried running another tank of the old fuel through the engine to confirm the diagnosis?

I spent a while last week helping to get an SC70 FS running reliably - checked all the usual suspects but couldn't stop it suddenly cutting for no apparent reason. The engine had stood for a while and I suspected foreign bodies in the carb. Pressure flushing it with a bicycle pump (a favourite technique of mine) didn't make any difference so we tried changing to a different fuel. It seemed to cure it during fairly extensive idling/transition tests...until taking it out for a test flight when it cut again on the flight line and then reverted to similar (but slightly better) behaviour.

There did seem to be longer between the cuts and the cure was eventually hit on when I tried running a tankfull of fuel through it at full throttle - whether this eased a slightly sticking cam follower, improved the piston ring seal, flushed the carb or allowed the needle valve seal to soften and seal better is unknown but had this transformation happened at the time we changed the fuel it would have been easy to jump to the wrong conclusion.

[Bob Moore]

As it happens I went to my model shop to buy some new fuel today and he was closed! So I may just try it one more time as I do have a good third of 5 litres left. I forget to mention that the tank of fuel I scrounged was (he said) one of best and very expensive. It was Weston UK Pro Synth 2000? New to me, but the SC did run beautifully on it. Had my local man been open I was just going to buy some more of my usual regular Model Technics Expert GX10 which is 20% castor oil, 10% equivalent Nitro, and 70% Methanol.

 

PS re TX servicing etc. I fly a few other models and don't get any glitches whatsoever with them, which I think rules out any probs with my tx?

Edited By Bob Moore on 11/09/2012 23:40:58

[Martin Harris - Moderator]

Bob, if you're running a 4 stroke on 20% castor there's a strong likelihood of carbon build up and gumming. I use Southern Modelcraft 10% for all my 2 and 4 stroke engines which has 2% castor mixed with 15% synthetic and find it works very well in all of them.

[David Davis]

I have seen a fellow club member spend all morning trying to get an engine to run properly. With a fill of fuel ftom someone else it ran perfectly!

Having said that whenever I have old fuel which is not fit for purpose I just sling a little petrol into it and use it up! But then I am a skinflint!

[Braddock, VC]

Posted by Martin Harris on 12/09/2012 00:11:34:

Bob, if you're running a 4 stroke on 20% castor there's a strong likelihood of carbon build up and gumming. I use Southern Modelcraft 10% for all my 2 and 4 stroke engines which has 2% castor mixed with 15% synthetic and find it works very well in all of them.

He isn't. It's a 2 stroke, unless SC have started making a 40 4 stroke very recently. See OP. However if the engine hasn't been run for some time castor has a nasty habit of gumming everything up; prosynth has a beneficial habit of stripping out all the gunge pdq. I still think it's the fuel though.

[Bob Moore]

@Martin. It's a 2 stroke. I have read that 4 strokes need a different mix.

@David. Nice idea. I'm a bit of a skinflint too and apart from that don't like chucking out something that can be revived. How much petrol in the mix? Try a little and see how it goes?

[bouncebounce crunch]

If you are regular readers of the magazine, Brian Winch is the regular engine garbologist with a penchant for using the same brew of carbolic in all his engines 4st or 2st , but, he also does state, read the instructions but otherwise engine warranty guy may give advise.

[John Muir]

Hi Bob,

Those are two very different fuels. Prosynth uses a very low oil content indeed and the oil is all synthetic (Fuch's Aerosave or some such I read somewhere). Effectively there will be more methanol content in it, so more 'bang' per litre. Also the oil and additives will have different properties to castor including the aforementioned cleaning action. The oil content is too low for the comfort of some manufacturers and might void a warranty, but I've heard it's top stuff. You may find that your engine will now run on GX10, now that it's been degummed, but it won't produce as much power and may not behave as well. A hotter plug might help, but it depends what's in it already. I'd suggest a Taylor std, Firepower 7 or an OS 6. Not sure about idle bars. I wouldn't bother with one. GX10 is what you might call an old fashioned fuel these days. 20% castor is a lot of pretty gloopy oil to put through a modern engine. I believe it doesn't actually contain nitromethane either, but a substitute developed when there was a nitro shortage years ago. Castor does smell good though.

Incidentally, I think SC engines are ported to run on low nitro fuel, so 5% should be perfectly fine and you could save yourself a bob or two. Higher nitro probably won't do any harm, but I doubt if it will be noticeably better. I run all my engines on either Model Technics Irvine 5% or Optifuel 5% both of which contain about 18% Klotz synthetic, with a dash of castor in the case of the Irvine. Works fine and is much easier to wipe off the model.

[Bob Moore]

Thanks for those valuable comments John.

Oh well, I've just come in from an unproductive 20 mins trying to get the sc40 to run properly on my regular GX 10. (Which as said has been in the shed for a good couple of years. It starts easily, runs but won't pick up well and the exhaust has a slight burbling at all revs (apart from screaming.) It also feels unreliable and liable to stop on throttle opening. I tried a couple of clicks out. Won't run, and couple of clicks in no improvement? I'm reluctant to mess with the slow speed needle on an engine now that I know it CAN run well. So definitely a fuel problem of some sort. It ran so sweetly on the tank of pro synth I scrounged.

Maybe I should start thinking about using a different fuel? I bought a brand new Irving 40 a while back and couldn't get that to run very well on my fuel. (And it wasn't as old then.)

I've always used idle bar plugs, but I just tried 3 or 4 idle bar and non idle bar plugs in this test (though only no 3.) With the non idle bar it wouldn't run at all?

 

I don't fly IC very often, partly cos of the unreliability I've suffered. It's a catch 22 situation. The trouble with trying different fuels is, at £15 a time for a can of something that might not be any improvement, it gets to be an expensive method of testing.

 

 

Edited By Bob Moore on 12/09/2012 11:51:41

[Bob Moore]

Blow by blow account of progress!

I don't recommend adding 20% unleaded petrol to the mix. (Adding petrol was suggested above. And successful.) Mine won't run at all on that. Maybe 20% was too much. It was worth a try. Time to buy some new fuel.

Edited By Bob Moore on 12/09/2012 12:41:15

[Martin Harris - Moderator]

Sorry Bob - confused two threads and thought we were discussing an SC 70!

For what it's worth, I use Southern Modelcraft 10% in all types of engine that I own with excellent and reliable results. It contains 15% synthetic (ML70?) and 2% castor.

[Bob Cotsford]

Southern Modelcraft 5% - I'm too tight for 10% - that works ok in all my ASP and SC engines whether 2 or 4 stroke including my SC40