Can somebody explain the concept of pinch test.

[SavagePower]

PINCH TEST-
Make a couple top speed passes, bring it in and pinch off the fuel line near the carb.
Start counting 1...2...3...
It should run for about 3 seconds before it revs and dies.
If it runs longer you need to lean the LSN.
If less than 3 seconds you need to richen the LSN.

When you pinch the fuel line, you are limiting the fuel into the engine.

If the LSN is running to rich, isn't it supposed to run shorter because it's going to use up the remaining fuel faster. More fuel to air.

If the LSN is running to lean, it's going to use up the remaining fuel slower. More air to fuel.

But the pinch test, why is it opposite.

 

[Pope]

First welcome to the family. and here is my advice; don't worry about it because this is a bad way to test your lsn settings. See this for tuning advice. https://www.hpisavageforum.com/forums/showthread.php?t=12260

This is why though when the lsn is rich the case loads up with fuel when you pinch the fuel line it keeps pulling air and mixing it with the fuel in the case till it becomes too lean to run. When it is lean to start with this process takes much less time than when it is rich.

 

[Shaun]

welcome to the forum my friend, glad to have you here with us...........

 

[SavagePower]

Thanks guys, I guess everyone has their own way of tuning. But the tuning guide by Purenitro is great and easy to understand.

I'm going to try it out.

 

[inb4lock]

This is why though when the lsn is rich the case loads up with fuel when you pinch the fuel line it keeps pulling air and mixing it with the fuel in the case till it becomes too lean to run. When it is lean to start with this process takes much less time than when it is rich.

This is correct.

 

[Pope]

Hope you get here going. We are always happy to help

 

[SavagePower]

Let me try to explain this concept that I understand it correctly.

If the LSN is set too rich, when idling, excess fuel builds up in the engine and therefore takes longer time to burn when we pinch the fuel line. Rich doesn't necessarily mean it's going to burn out faster, it just means that it draws more fuel into the engine.

If the LSN is set too lean, engine only has to burn off the fuels after the pinched point on the fuel line, so therefore takes shorter time to burn.

 

[Bankrupter]

thats right...its burning fuel that is in the mill case that should not be there at all. but if its rich then it mis leads you setting you HSn and its a nasty cycle that kills the mill.