Mower turns off when letting off the throttle

[logert gogert]

Hey, I recently straight piped my mower ( don't ask why ) and for the first couple days it was fine, but then I noticed that one day I went to go move it in the shed, I started it up let it warm up for about a couple minutes ( like I always do ) without revving up at all, the I drove it over to the shed and since I have a foot throttle if you let off the gas it does it quickly, so I let off the gas and it turned off once it got to idle speed.
I went to start it up again, started up perfectly like it always does, started to drive and once again let off and it did it again. Started it up again and this time slowly let off the gas and it did NOT turn off when you let off the throttle , parked it and went inside.
The next day I went out to go check it out, did the same thing once again, but still if you let off fast it cuts off, let off slow it does not.
Then I put the muffler back on, and it would not cut off wether you let off slow or fast.
Any body know why it would cut off straight piped ?
The motor runs much easier straight piped besides that one issue, and I would like to keep it straight piped,
Please help

 

[Rivets]

If you would learn what makes an engine work, as I instructed a while back, you would know that an engine needs back pressure to operate properly. Using no muffler or have a straight pipe are the same thing and provide no pressure meaning exhaust valve will not close properly.

 

[logert gogert]

If you would learn what makes an engine work, as I instructed a while back, you would know that an engine needs back pressure to operate properly. Using no muffler or have a straight pipe are the same thing and provide no pressure meaning exhaust valve will not close properly.

That is what I originally expected, I just wanted to come here to clarify that as for your knowledge is far more advanced than mine, thank you for replying rivets.
But how much back pressure do you think I would need, because like I said, I would like to remove the original muffler and maybe put a much less restrictive one on, because the one on now has only 2 holes big enough to barely fit the tip of MY thumb in, so it's very restrictive

 

[ILENGINE]

Something else to look at. Look at the throttle position on the carb, and check the stop point in relation to the idle speed adjustment screw. If you are letting off the throttle all at once, and the adjustment screw allows the throttle plate to completely close can cause the effect of shutting off the engine because it shuts off all air and fuel flow into the engine.

 

[logert gogert]

Thank you guys