stratified intake third hole ?

on a pp4218avx, in replacing the carburetor it has the typical carb base gasket for that portion of the carb that mates with the plastic intake on the engine. being a "statified" setup it has the same diameter butterfly on the top (mechanical secondary) which is part of the carb and is connected by the little black rubber hose. But on the plastic intake, in between those two airflow paths that are obviously sealed, there is this hole maybe 3-4mm in size. What I'd like to know is why this hole is there. As u can see in second pic, and as far as i know, there's no gasket that covers it and it almost gets half covered by the carb... but with no gasket there. Seems like a design oops ?

some other info: https://www.ereplacementparts.com/poulan-pp4218avx-gas-chainsaw-parts-c-16962_17147_128670.html

don't feel like pulling the intake adapter off but it seems the cylinder is no different than any other 2 stroke single cylinder of this type: has one intake port that the carb flows air/fuel/oil mixture into, and at the bottom has the port which is the impulse port that connects up to the carb to make it's fuel pump work.

so this "stratify" nonsense is all in the intake ?

seems like all that is happening is you have your basic ? mm throat carb for a 42cc single cylinder... just like the mm diameter will be a little more for 50cc engines, and even more for 60cc engines, and so on. Now add this intake/carb setup with a separate mechanical butterfly to allow ~double the aiflow at 1/2 to full throttle? There's some orifice or something in the intake adapter, because otherwise wouldn't that top butterfly just act like a big vacuum leak and never suck thru the carb when that top butterfly opens?

Not familiar with that particular model, but fresh air is sucked through the top butterfly and is the first to enter above the piston. It purges the spent exhaust out. On an old school 2 stroke, a small portion of the mixed fuel purges out the spent exhaust.

The hole in the middle you're referring to....I'm guessing it's just a casting hole. Or maybe there's a recessed mounting screw inside?

yeah i think it's a casting hole, it holds water and air pressure.

and the online pics are not correct either I suppose, looking up youtube stuff on stratified 2 stroke there's an entire separate port in the cylinder casting for the "stratified" air flow which is air only.

what would happen if I undo the carb linkage, and in my pic the top butterfly that lets in air only never opens?

what would happen if I get a paperclip or something for new linkage and adjust the time and amount of the upper (stratification) butterfly opening?

Title sounds like weird porn. Had to do it, sorry.

So that hole holds water?

Lightning Performance said:

Title sounds like weird porn. Had to do it, sorry.

Click to expand...

Wierd Chinese Porn

r7000 said:

yeah i think it's a casting hole, it holds water and air pressure.

and the online pics are not correct either I suppose, looking up youtube stuff on stratified 2 stroke there's an entire separate port in the cylinder casting for the "stratified" air flow which is air only.

what would happen if I undo the carb linkage, and in my pic the top butterfly that lets in air only never opens?

what would happen if I get a paperclip or something for new linkage and adjust the time and amount of the upper (stratification) butterfly opening?

Click to expand...

I'd just use the OEM linkage and run it