I noticed that I've got an air leak somwhere in my fuel line (YS 1.10)
While trying to find out where the leak was comming from, I found that if I sucked on the line into the regulator (ie fuel in) I could draw air from the reg.
Is this my problem?

Can anyone out there tell me if I should be able to draw air from the regulator via the fuel line?

Ok, I've cleaned out the regulator.

If I close the main needle fully I cannot draw air through the fuel feed line but if I open it a turn I can.

I would really appreciate it if someone could PLEASE tel me if this is normal or not.

I can find no other air leaks in the fuel system.

Thanks.

OK, let me say first that I am not an expert, but I have run YS engines for a while, but I can see you are desperate so I will offer my opinion. I would think that this is not your problem because from what I understand the only purpose of the regulator is to stop fuel from flowing into the carburator. Since there should be constant positive pressure on this line coming from the tank, it shouldn't matter if you can suck on this (in fact, you should be able to I think), the main test would be to try and blow into it and see if air goes through. My reason for thinking this is, from what I understand, the regulator is open once per revolution by a hole in the crankcase that lines up with a hole in the regulator housing allowing crankcase pressure to force the regulator open to allow the proper amount of fuel through. Now, I have a couple of questions for you: 1) Have you run the engine since you cleaned the regulator? and, if you have, and it's still not running correctly, let's go back to the beginning 2) What makes you think it is an air leak? I want to make sure you're chasing down the right culprit here.

Let me add my 2 cents ( for what it's worth ). An air leak in your fuel line really can't happen. If there is a leak in that line, it would be a fuel leak, since that line is under about 8 lbs pressure. Are you sure you have a leak? What are your symptoms?
Paul

There's a lot of misunderstanding about the regulator on these engines. There is no pump, and the regulator does not regulate the pressure coming from the tank. Rather, it regulates the flow of fuel into the engine, and prevents the engine from being flooded when running at a low or idle speed. As I understand it, here's how it works. As the engine rotates, crankcase pressure is sent from the bottom section of the regulator back to the tank, through a check valve that forces the tank to hold the pressure. Crankcase pressure actually fluctuates from "positive" to "negative" as the piston moves up and down in the cylinder, so the check valve causes the pressure flowing towards the tank to be held and trapped in the tank while the piston is moving the other way. The result is a tank that has a constant positive pressure inside it, which in turn forces the fuel out the clunk towards the engine under pressure. As long as the engine is running at a mid to high RPM range, it is burning the fuel as fast as the tank can deliver it, and everything is fine. But at low speeds, especially at idle, the flow, or volume, of fuel would be too much and would flood the engine, so the regulator comes into play by reducing the flow. The adjustment screw on top balances between the crankcase pressure coming from the bottom, which is ported into the case, and the spring-loaded valve on the other side of the diaphragm. What you are trying to do is find the proper tension on the valve so that at low speeds the valve stops the flow and the engine draws fuel by vacuum just like any other engine, but then at higher speeds the fuel can flow at at greater rate based on the demands of the engine. At high speeds the crankcase pressure below forces the valve to open and allow fuel flow, at lower speeds the spring overcomes the crankcase pressure and shuts the flow off, preventing flooding.

Now to answer your question, I think it is normal for you to be able to draw air through the fuel lines. The carb has to be able to draw fuel at idle since it isn't being pumped into the carb below about 2000 RPMs. When you close the needle valve, that stops the air flow, as it should. The way to find out if you have a leak is to run the motor for a few seconds, and then leave all the lines alone for about 15 minutes. Next, remove the fuel dot from the vent line and listen for a hiss. If you don't hear one, then get some dishwashing liquid and run the engine again, but this time start painting the lines and the regulator with the soap. You should see the bubbles when you find the leak. And an air leak will only be seen on the pressure side, as a leak coming from the clunk side of the tank will result in fuel dripping or spraying from a fuel line.

This is all subject to correction by one of the YS experts who lurk around this forum. I may not have all the facts exactly right, but you can read some of this info on Troy Newman's (a real YS expert!) website at this link:

http://www.patternflyer.com/troy/?page_id=13

Hope this helps!

David

Yeah, that's kind-of where I was going. If the problem is that the tank is not holding pressure, this is the only place an air "leak" can exist in the pressurized system, and it could be something as simple as a bad or improperly installed check valve.

Hi all, thanks very much for the replies.

I have not yet run the engine since cleaning out the regulator, I could'nt find anything in there btw.

After running the engine it holds air pressure ok, but when I drain the tank it draws off bubbly fuel, ie fuel and air (even starting with a full tank. So I was thinking "where is this air comming from". It did'nt used to do this untill I got down to the dregs.

Make sure all lines are hooked up properly: fuel tank vent to pressure side of regulator w/ check valve in the line, arrow pointing in direction of tank, and the fuel supply (clunk side) hooked up to the regulated side. Run the engine and see what happens. It sounds to me like your fuel lines may have gotten reversed somehow, and the crankcase pressue is blowing out through the clunk causing bubbles in your tank (of course, the engine wouldn't run long, if at all, if this had happend). Let us know how it goes.