Hi all,
I have a question on the working principle of the Check valve / Fuel injector of the YS DZ Engines.
Is it suppose to leak fuel i.e. breath during the cycle ? My YS 170 DZ CDI has started to leak fuel from the top of this Check valve but the performance has not been affected.
I pulled it apart and noticed the valve is not sealed.

rgds

Yes, it might leak fuel, it is normal. I mean, get wet, not dripping.

Regards

Thanks Apereira,

The 170 dz was leaking a lot of fuel to a point that I was running out of fuel during flight so I replaced the top bit with the diaphram .......see how it goes.

regards

The only way it could leak that much, is if the cap was loose or a hole in the diaphragm. Don't know how it would get holed though.
I'm surprised the engine didn't go lean if it was leaking that much.

Yes I know but it did run ok mind you with these engines you hardly ever have to use more than 75% throttle so leaning out was probably not an issue....

regards

Mavros,

Make sure you do not have a leaking hose on the engine, as that valve is supposed to removed most of the air out of the line, so excessive fuel coming could mean that.

Regards

Alejandro

Yes, I was thinking the same.

Run the engine on the ground with the cowl off. It will be easy to see any leaks.

Thanks Alejandro and drake,

I have replaced the top of the valve and the leak has stopped.
Just curious however .Is the valve like a breather that bleeds any trapped air out of the system?
How do you bleed the air otherwise.

many thanks

Could you see anything wrong with the valve top/diaphragm?

I use the Tettra bubbless tanks. I've been using them for 15 years and never had a problem with air in the fuel.

I don't do anything special when fueling. As long as the fuel pick up is always in the fuel, then it won't get air in the system.

Some bubbles might come from the foam clunk, and other form air leaks due to punctured or worn hoses.

Regards

Thanks Alejandro,

Do these air bubbles get purged out through the check valve or do they stay in the system ...

regards

Not 100% sure, but I doubt if the check valve would get rid of air bubbles. That's the purpose of the foam clunk and why it's important not to have air bubbles in the fuel before getting to the engine.
Like I've already said, I haven't had any air in the fuel using the Tettra bubbless tank.

Gday Drac,

I have never used the Bubbleless tank so I can't really comment on that,
I do use a normal F3A tank with the YS foam clunk and don't have any issues .

From my experience with these engines the biggest problem is keeping the fuel temperature below the boiling point of the methanol with is quite low.
I f you can manage this you will prevent the fuel from cavitating inside the pump.

It is very important to have good airflow around the engine .......this is something that model designers don't address very well.
I was very impressed to see mr Najary in his build of the Fantasista design a cooling duct for the ESC.

regards

1. From your posts it sounded like you have problems with air bubbles in the fuel, but you say you have no issues?

2. Cavitation is usually associated with centrifugal pumps caused by a restriction on the suction side. I've never had a problem with fuel pressure or overheating, even in 38+ deg C temperatures.

3. More important is to have enough exit area.

Mavros,

it takes enogh air bubbles to keep the engine running,

Regards

Gday Drac,

Mate its always informative talking to you over the net.As always these threads tend to digress from the original question which in my case was fuel leak from injector.
I have fixed the problem by changing the diaphram .
As far as cavitation is concerned what you say is true but it comes in other forms as well like constricting a liquid which is what I think is happening in our engines pumps.

regards

What problem are you having with the pump?

I've read of some having wear issues, but I've never had any pump problems at all.

Over the years, there have been a number of problems people have experienced, of which I haven't. The only real problem I had was with the backplate sensor when the CDI's first came out. I came up with a fix for that and had very few issues with the 170 and less with the 175. Well over 400 flights on my 185's now and the only problem is the broken carby housing, which is a first for me.

Maybe I've been lucky, but I prefer to think it's because I know what I am doing. Lol.

Hi Drac,

No problems with the pump just the leak from the injector which I replaced

HOWEVER that did not fix the fuel issue .....I now notice that a lot of fuel is ejected from the carby which I think the timing is out ....I have replaced the bearings and maybe I put timing out during assembly.

The interesting thing is the engine starts and runs ok but spits half the fuel out the carby

regards

Put the piston at TDC on compression. Take the cam cover off and the dot on the cam should be at the bottom. I've actually found checking it this way, the dot is slightly to the left.

Mavros,

Just asking, are you sure the fuel is coming form the carb? Usually I get a lot of oil when the header "O" is bad, and I really doubt your engine has an issue with the timing, but who knows.

Is the Glow/Spark plug ok? the regulator is not overly rich? If the regulator is rich that will happen also, that's why I ask.

Regards

Alejandro

Yes, a blown header O ring will put a lot of fuel at the back of the engine.

I can run the regulator very rich, untill it starts misfiring without any excess fuel coming from the carby. If the timing was out that far, I would expect it to be running very rough and not making power.

It does sound like a fuel leak to me.

Hi Alejandro,

I have the cowl off and definitely from the carby....

will report further later

rgds

OK so here is the latest.

Took the engine out of the XIGRIS and put it on the test stand.Started the engine and fuel sprayed everywhere initially it appeared to be coming out of the carby but on closer examination with reading glasses on this was not the case.
The fuel was coming from hose next to the carby ....Hose replaced and problem solved'

Moral of the story put your GLASSES on.

rgds and many thanks

Happy you found the issue. Stupid easy fix once you identified the problem. Wish they were all this easy!

Ken

I've had that one hole as well. I was looking for loose back plate bolts and blown gaskets untill I found it.

It's a PITA to get that one on, so I use needle nose pliers and that's what caused the hole. I still do, but much more carefully