Carb Question - WHAT'S A BYPASS TUBE ? ! ? !

[home made tunnel]

I'm Stumped - I figured this little 5hp Force motor would be a simple fix (Barn Find for free).
I cleaned it all out, great compression, but it surges and won't idle, at all different sorts of needle settings, all the same... just surges and dies like an old briggs and straton hitting the governer.
All the gaskets seal well and the reed valves are tight and sealed.
I'm guessing it had something to do with me F**king up this little "bypass" tube. I kinda bent and jacked it, but put it back in.

I can't find anywhere on the internet what this stupid tube does, how it operates, etc. Therefore I can't even understand how to fix or diagnose it. Can anyone learn me something?
I ordered a new plug and tube from marineengine.com anyway.

405779

[Motv18]

It bypasses something... had to

should be sorta like a fuel pressure bypass. Merc has some as well. Unless pinched or not seating it should function

the surge i would start with vacuum and fuel. Make sure the intakes buttoned up tight after looking at the reeds and carb gasket sealed. Double clean the carb. Circuit adjustment might be off. Rich can make it pulse surge is messy.

If all looks good you end up in timing electric.