YS120 - air in fuel line.

[Malc1]

Yeah I have spotted that hole and you can certainly feel pressure at this point when you turn the motor over with a plug in.
Engine has only had the head and back plate off at the moment but I'll watch this.

I'll restart the motor see what it runs like and see about leaning the mid range up a bit.
What's your needle setting here? - as a reference.

Certainly got to look at burning of surplus fuel though whatever I find.At the moment I'm only attempting to clear the engine by spinning it over with the starter.

[tonystevens]

Both my needles are set at around 1 1/8 turn with the mid a click richer than the high

[Malc1]

Diaphragm changed,needles removed and carb flushed through.
Regulator reassembled and checked for leaks and refitted.

Idle reset at just less than 1 turn out and hover leaned to 1 1/4 turns out.

Engine restarted out in the back garden earlier.

Still not running right.
Air in the fuel line still and an uneven idle.Leaned out the idle a bit more but didn't make much difference other than starving the engine of fuel and it cutting out when you open the throttle up.

Haven't had a new check valve come yet but have a feeling that it may not help.

[tonystevens]

I don't think you've got anything serious to worry about there, YS don't idle smooth like OS, they tend to be smoother in flight. Looks like a brand new engine, have you flown it yet? EDIT: Just remembered you've put 6 gallons through it lol

[Malc1]

Yeah had the engine since middle of last year and had perhaps 6 gallons through it.I always wipe the whole lot down after flying.

I'm pretty sure this used to idle much smooth than this and I couldn't remember noticing the air bubbles before - you reckon that sounds OK to you then?

The main problem I have with the helicopter is the tail wag that I get when hovering and I was suspecting the engine was the cause.It could still be I suppose if that mid range is a bit rich still.

[tonystevens]

Doesn't sound any different than mine tbh, the bubbles your seeing are probably being sucked in through the top of your magnet, not much fuel in that tank and the magnet isn't fully submerged and yes a rich mid could make the tail wag. What does it run like in flight?

[tonystevens]

BTW, you need to double up the tubing on the piece your seeing the bubbles in too, its a very slack fit on the nipples.

[Malc1]

Yeah that fuel is getting a bit low.

That fuel level was up to about 3/4 of a tank when I started it up earlier.
Runs the same with the air bubbles with a full tank or less than half.

Runs and sounds OK and has a good smoke trail when hovering and at full power.

I'll leave that mid range at the leaner setting then to see if it helps with the tail.I'm pretty sure that this has been leaner than it is now and didn't help much though.

[Malc1]

Just stripped the engine down completely after it developed a major rattle while flying yesterday.
Turns out that the back bearing has failed just short of falling to pieces.A bit lucky and may explain some of my running problems.
Slightly marked the piston and crankshaft as well.

There still air in that short piece of fuel tube when idling and I expect it will still be there when I get the engine back together.

[Sticky Stick]

Hi Malc,

we have a couple of Y.S 120's with the same problems as yours. Air between the reg and the carb but none before. This is with lines being doubled up etc.

I cannot see how this can be right. The reg should be supplying the carb fuel ,without air at the right pressure for the carb to work. Air bubbles going through to the carb will only upset the balance and make the engine run rough and inconsistent which is what we are seeing.

I am wondering if there may be a fault with some of these regs? Air is being drawn in somewhere. Does anyone know if the 120 is working off the same amount of tank pressure as the .91's?

Has anyone tried a reg off a working .91 on a 120?

[Malc1]

I don't think it's right either - but what to do about it.
Don't know about trying a regulator of a '91 as it looks to be exactally the same thing.All the part numbers are the same.

And as mentioned I've changed the Diaphragm and all the fuel tubing plus am using modified tank bungs with no difference at all.

I'm hoping that I can just ignore these bubbles and once I've rebuilt the engine it runs better.

I have had to order a new piston and ring along with the bearings and have one of the new modified heads on the way to try also.

A bit of a nightmare with getting YS spares as well - I have just had to order from Germany and pay a load more than UK prices

[jwatts007]

I was chasing a problem with one of mine in the 700...I changed and checked all the usual suspects...I was using OS no 10 plugs...then I put a NO 8 in it and it was fine...seems like they like a hotter plug in warm weather and it idled so much better with a hotter plug allowing me too turn the needle in some...the YS bearing was not a lot of cop either its so much nicer fitted with a SKF bearing...can you tell me the part number of this new head or put a link up to it please....thanks...

[pcollins]

Malc1 hope this will help and answerer the bubbles in the line question

I have spoken to YS today which I have posted there response here http://www.rcheliaddict.co.uk/engine...fuel-line.html

Your youtube video shows the same amount of bubbles in the line as I have and YS have said this is not a issue at all.

[Malc1]

So basically,ignore the bubbles and look for other reasons as to why your engine is not quite running properly.

Regarding the modified head - I have it coming from YS in the US after making a phone call.
It seems that even YS in Japan are unable to supply it for a few months as they are working on a revised 120 engine.(I emailed them and actually had a reply back).

A link to further info.

YS120SR revised head

[Malc1]

DSC05222.jpg

Arrived this morning.
New head on the left.