How to test impulse line?

[wkz]

I have a 52cc chinese saw, it looks like this:

The problem is that it wont start. I can get it started for a few second by dropping a few drops of fuel either from the spark plug hole or directly in the carb air intake, but once it consumes that fuel it stops.

I took the carb apart and noticed it was "dry", unlike other times i took it apart when a bit of fuel always comes out.

I tried a new carb from another machine that is 100% new, so I know that carb is ok. Still wont start on the old saw. Opened this new carb and it's also dry. So it looks like it's not sucking fuel.

Both fuel and impulse lines are clear, I tried blowing into them and air goes through fine.

The engine seems to have normal compression. I don't have the tools to test it, but when pulling the cord, it feels the same as the brand new machine. I checked all the gasket from the outside, and they seem fine.

Is there a simple way to test if the impulse line is working fine?

I know how it works on the carb side (and im 100% sure both carbs work because I tested them on the other machine). But I don't know how the impulse line works on the engine side, I assume the piston goes down and up and sends pressure/vaccum to the carb pump/membrane.

I tried lightly clogging the end of the line with a piece of paper tissue, and cranking the engine, and the paper didn't move, I was expecting it to blow it out or at least move a bit. I also tried cranking the engine with the impulse line in my mouth, and can't feel anything.

What else can I check without opening the crankcase?

 

[Andyshine77]

Sounds like the you have no case pressure or the impuls line is blocked, maybe the case wasn't fully drilled all the way through. Hook a vacuum pump with the gauge up to the line, vacuum it out of it, then turn the engine over and see if the needle on the gauge moves at all. Honestly you never know what your going to get with a saw like that.

 

[SEAM]

...can you draw fuel up the fuel line? It may have a crack in the tank or the filter may not be submerged in fuel (there is fuel in the tank, I assume ).
Also, you should be able to feel the impulse action with your finger or see it by spraying some WD 40 into the line.

 

[wkz]

I tested cranking the new saw with the impulse line in my mouth and could totally feel it blowing/sucking air. So since the old one did nothing, and I couldn't find anything from the outside, I opened the crankcase, the gasket was blown in the part that separated it from the oil tank, I am guessing that was the issue.

 

[Andyshine77]

I tested cranking the new saw with the impulse line in my mouth and could totally feel it blowing/sucking air. So since the old one did nothing, and I couldn't find anything from the outside, I opened the crankcase, the gasket was blown in the part that separated it from the oil tank, I am guessing that was the issue.

Yes that would do it.