At the end of my tether (nearly)

[Rusty C]

Bob I did blow into the tank but skipped the bowl of water bit, I thought I would have noticed it leaking anyway, I will check that also thanks.

Dean The Carb is defo higher than the tank centre so I am not sure if the syphoning is plausible, But I will put in a fuel line loop to cover the base so to speak.

I hope the the fuel line bubbles and low needle reset will help me resolve this matter.

rusty

[YakMad]

Rusty,

It's sounds the tank may be be too high, I have found that on some inverted for-strokes that the tank needs to be much lower than the carb more like at the the position were the inlet manifold enters the head. SC, ASP and Magnum's all suffer from poor quality 'O' rings on the main and idle needle and don't last too long if the needle's are abjusted alot, push a small piece on to the threaded part of the main needle for a start and re-install, the idle needle may need a new 'O' although I have used silcone sealant to cover the outside of the idle needle as a temporary measure to eliminate a potental air leak during testing. An easy solution to identify if the tank height is the problem is to get a small tank hang it on the side of the model (rubber band or tape it in place) at a lower height than the carb, plumb this tank to the engine and re-run it, you can then re-positon it to see up or down to see if the idle is effected.

[John Muir]

Rusty,

You've got bubbles in your fuel line. This can only mean one of two things. You have an air leak into your fuel system or you have a fuel foaming problem.

Air leaks, see the other posts.

Fuel foaming, there's a few things you could try. Foam loosely packed around the tank to isolate it from the airframe would be good, but probably isn't possible in this case. Tightly packed foam is no use as it will still transmit vibration. A different clunk designed to stop bubbles getting into the fuel line. Or different fuel. Most fuels nowadays seem to contain anti foaming agents, but I suppose some are better than others. Might be worth experimenting.

I don't think retuning your engine will help until you get rid of the bubbles and I doubt if the problem is syphoning from what you have said about tank position etc. Check yourself. Just fill up the tank and open the throttle. If fuel constantly fills the carb or drips out, it's syphoning.

HTH, John.

[Josip Vrandecic -Mes]

Dear Ian Jones,thanks for info abt Cline reg. and Ironbay reg.I've helped a lot..so, I appreciate to Your input

Joe

[Rusty C]

YakMad

I changed to O rings before I even bench ran it as I have read about the quality issues with these things but will check this again before a re test. I hope the tank position is ok as there is nowhere else for it to go and then it a dead duck!

John

You are right about the tank isolation as there aint much room in there maybe about 5mm either side after I had paired some material back.

As for the clunk is that something like the heli boys use, that foam covered ones? Your right to about trying again until the air bubbles or foaming fuel as been sorted, just no chance of getting a tune in this condition!

I am off to check for this syphoning now fingers crossed.

rusty

[John Muir]

Yes Rusty, felt filtered clunks are what I had in mind, but they seem to be aimed at petrol and jet fuel users and I don't know if they'd be ok with glow fuel. The other type is the sintered bronze clunk which I've seen for sale at RCWorld.co.uk and that's definitely fine for glow.

I can't remember if it's been mentioned yet, but if the fuel is foaming it's because of vibration, so check all your mounting bolts are fully tightened and your propeller is balanced. Also check the running with the airframe rigged for flight i.e. with the wing bolted on, as that can change the resonant frequency of the airframe as a whole.

Hope you get it sorted.

John.

Just noticed that Just Engines has a felt clunk specifically for Glow engines.

Edited By John Muir on 11/12/2012 20:20:38

[PatMc]

Foaming fuel won't cause bubbles in the feed pipe with a normal clunk tank so long as there's enough fuel to cover the clunk. The air must be entering between any section of the clunk tube within the tank that's above the fuel level & where the bubbles are visible before the fuel tube connects to the carb.

[Rusty C]

Well I have done the checks for air leaks none to be found, So I have refitted the tank with a bit of foam for vibration, I also put in a nice uphill loop in the feed line. I have put new O rings on the engine including an additional one where the carb meets the intake manifold.

John thats a good point about the wing being on the airframe that never crossed my mind And I will also admit that I have not balance the prop. And thanks for the clunk heads up I was trying to find a glow one for long enough.

Once I have received new assortment of plugs and new glow driver I should be ready to give it another shot probably friday at this rate.

One more question, The temp up here is barely getting beyond 0 should I be looking at a richer mix when cold?

[Braddock, VC]

Couple of things, if it was cold outside when you started having your problems there are a couple of issues worth considering especially as you said the engine ran fine before.

Around freezing point castor oil starts settling out of the mixture it's in. Model Technics contest 10 has klotz oil which has quite a high percentage of castor. Parts of the castor settle out and look like little white globules which can choke the fuel spray bar. ( try leaving olive oil or castor if you have it in a fridge overnight and you'll see what I mean) This reaction is reversible ie when it warms up the stuff goes back into solution.

Before you go looking at other issues try bumming a couple of tanks of fresh Prosynth 10% which has all synthetic.

Secondly cold weather doesn't help methanol vaporise, a lot of folks put 5% petrol in to assist in cold weather starting and running though I've never tried myself. Others swear by a 5% increase in nitro i.e. up the amount to 15%, again I've stuck with 10% prosynth and had no problems.

I'm not saying that it will cure it but it's a cheap fix if it does.

 

Edited By Braddock, VC on 11/12/2012 23:04:54

Edited By Braddock, VC on 11/12/2012 23:05:59

[PatMc]

Posted by Rusty C on 11/12/2012 22:27:53:

Well I have done the checks for air leaks none to be found,

I thought you said there were bubbles visible in the fuel line to the carb ?

[kiwi g]

Try running with a vent and feed pipe only , no exhaust pressure .. sounds like a syphon happening and with added pressure fom exhaust it will be worse.

[Rusty C]

Posted by PatMc on 11/12/2012 23:19:07:

Posted by Rusty C on 11/12/2012 22:27:53:

Well I have done the checks for air leaks none to be found,

I thought you said there were bubbles visible in the fuel line to the carb ?

There was bubbles visible PatMc but could not find any leaks no matter how hard I tried.

rusty

[Rusty C]

Kiwi

That sounds like a good plan if the next test fails, I noticed that the vent pipe had straitghened out so it was just out level with the bung so maybe this didnt help much.

rusty

[Max50]

Hi Rusty C,

I had bubbles in my fuel line. No leaks in tank or tubing. A mate at the club told me to check the klunk.

I carry my model nose down to stop oil coming out of the exhaust. Didn' think. My klunk tubing was close to the correct length, but it still allowed it to double back in the tank. When rattling the tank i thought it was OK! but it wasn't. It had doubled back, causing the bubbles.

Just a thought as you may have shaken the tank but not got the Klunk out.

Mal.

[Cookson]

A very interesting thread & I will be keen to know the outcome.

I have exactly the same problem with an OS91FS in a Tucano, even brought an SC91FS & gave the same problem. Checked & rechecked tank, plumbing, needle, carb, valves, plug to no avail.

Have now put an Irvine 60 2 Stroke in & runs great.

Next step was I bought a test stand & bolted the OS91FS to the workmate & to be honest wasn't expecting what happened next, you guessed it, fired it up 1st time & ran great.

The only difference is in the Tucano it's inverted, on the test bench it's not.

[YakMad]

@Cookson, A big problem with ARTF's is the poor quality and soft nylon engine mounts supplied. Engines run best when mounted to a solid structure, this can be the reason why an engine which runs great on the bench runs poorly in a model, four-strokes are more affected by this than two-strokes.

[F2bflyeressex]

Hello, a couple of bits that might be worth trying,

1. add a piece of silicon tubing over the outside of the main needle valve assembly, it is not unknown for these to leak around this area and cause inconsistent settings (although not normally on the lower end usually at the top end of throttle opening)

2, a trick we use often on control line aerobatics to prevent fuel foaming is to add 1x squirt of armoural car cockpit cleaner to a gallon of fuel, the silicon content in this product seems to stop all foaming and does not affect the running, But only use just enough.

I know it sounds odd but it does work.

regards

gary

[Delta Whiskey]

Had similar problems myslef, checked and replaced all plumbing - still the same, in the end it was solved by putting a complete new tank in, I suspect the bung or brass tubing was letting air in somewhere - maybe worth a try and cheap too !

Edited By Delta Whiskey on 12/12/2012 09:57:53

[PatMc]

Posted by Rusty C on 12/12/2012 07:25:11:

There was bubbles visible PatMc but could not find any leaks no matter how hard I tried.

rusty

If there were (& still are bubbles) visible in the fuel lead then they must be an air leak between fuel tank surface & where the bubbles can be seen. Forget frothing, syphoning & airleaks at the carb, if you can't locate this source change the tank & fuel lead.

[John Muir]

You don't have to have a leak to get air bubbles in your fuel line. Foaming occurs when vibration of the right intensity and frequency shakes the fuel in the tank around enough for the air in the top of tank to 'dissolve' into it in the form of microscopic bubbles. These micro bubbles then clump back together as the fuel heads up the line towards the engine and become visible as normal bubbles. It's a well known problem, hence the use of anti foaming agents in fuel and felt/sintered filters. It's a problem I've only personally come across once, when I packed too much foam around the tank in my old Wot 4. The engine suddenly wouldn't run properly, especially at idle. I took some of the foam out and the problem went away. It used to be suggested that you add your own anti foaming agent in the form of a surfactant like dish washer fluid (a couple of small drops per gallon apparently), but I've never done that. Four strokes are more shoogly than two strokes so vibration becomes a bigger issue.

I haven't had a lot of ARTFs but I did have a Seagull Boomerang a few years ago to get back into flying after a lay off and I was surprised to find the tank was a tight push fit through holes in two formers with no attempt to isolate it from vibration at all. Seemed like a very poor piece of design to me, but, having said that, it worked. I think vibration only gets to be a nuisance if it just so happens that all the various factors (airframe, tank mounting, engine mounting, engine type and speed) just happen to come together to shake the fuel just right so that it froths up nicely.

[Rusty C]

Thanks for all the input lads very helpful.

Friday lunch time is my next chance to have another stab at it with all the new mod's done, If the result is not any better I will change the tank for a Sullivan flex tank which I have to hand, These tanks are soft on their own by design so this coupled with better quality maybe be the last chance this SC gets! I have also removed the filler valve and will just block up with line stoppers to eliminate all chances of air getting in.

I will probably throw In my 2 stroke Irvine as I want to have it flight ready for our boxing day fly in !

I will of course keep you's posted of the outcome, I dont like to be beaten so I am going to try very hard to get this SC playing ball. I Think it will fly and look better with a 4 stroke anyway!

rusty

[Rusty C]

 

Just a few pics of the instal guys, You can see the bit of foam at rear of tank to stop it moving back and fourth I also trimmed down the tank bulk head piece and inserted more foam in ( not seen here)

You will also note the fuel feed line rising up over the battery mount, where as before it came straight out to the carb ie between the mount .

rusty

Edited By Steve Hargreaves - Moderator on 13/12/2012 08:51:59

[Steve Hargreaves - Moderator]

I'm a bit late to this thread & I can see you've already had some good advice Rusty but just to chuck in a couple of thoughts......

OS F plugs are great....expensive but great....stick with it!!

Might the internal fuel line between the clunk & the tank outlet have a tiny hole...as the others have said until you get rid of the bubbles theres no point touching the needle.....

Are the tappets set correctly?

Are you letting it warm up enough before tuning the needle......its bloomin' cold & 4 strokes have a lot more mass than 2 strokes to get hot. The engine should be at running temperature before you adjust it......I would say you need a good 5 mins at about 1/3rd throttle to get it fully warmed up....

I know you don't want an on board glow but will it run OK with the glow still attached?

It should be solve-able Rusty.....I have an ASP70 inverted in my Yak54 & its never stopped on me...

[Rusty C]

Hey Steve Yeah I have ordered another OS F just in case my one has given up. I have checked for holes and leaks till i was blue in the face so I am nearly sure its good.

But you may have a point about the warming of the motor, I was letting it sit to warm but not as long as you suggest, As I said in another post it was around zero degrees so it possible it was still way to cold.

And yes it will round with the glow driver on, Which made me think to was rich but when leaning out not much was happening then confusion took over and i was lost. Now that I am back at the factory settings I cant see how I can go wrong.

Will update you's tomorrow.

rusty

[daniel barton]

this might be a long shot, but as i live by the coast, the cold constantly has a hand in my engine troubles and this is what i do to cure this:

i get a teatowel (an old 1 at that) and a

a bowl of freshly boiled kettle water.

put the towel into the water for about 5 mins so that it absorbs the water within the bowl, then take it out and wring the towel of all excess water so that ur only left with a warm damp towel.

making sure that your carb is closed (just incase of water drops into the carb), place or wrap the towel around the cylinder head for a good 10 minutes.

as the towel warms up the cylinder head, it also warms up the fuel inside the engine (if any) and will make starting alot easier, just make sure that you have you glow starter to hand so that when you remove the towel, you can put the glow starter on straight away and start the engine.

just alittle note on the bubbles, i had the same problem with my os40fp and what was causing it was a blow back of the engine caused by a partailly blocked carb causing air to be pushed back into the fuel tank, so try removing your carb and give it abit of a clean.

also are you hand flicking or using a starter, as it seems that flicking an engine over by hand can also cause this (again from experience) as we cant spin the prop quick enough.

try those and let me know how it goes