since you didnt reply to my question I will just say that if you didnt know what your popoff was originally and changed the springs, even if they look like the old, you may have lowered your popoff accidentally and now have an overly rich carb.
I am not trying to be an all knowing D I C K but I have seen sooo many times where people supposedly "rebuilt" their carbs correctly. If you just changed a few gaskets out that is not my definition of rebuilt. If you didnt verify that the small holes in the throat under the throttle plate are clear, that the return lines are not clogged full of debris( which can still flow but be restricted from crud) check the popoff before and after, verify when doing the rebuilt pop that the gaskets are holding and not leaking, change all the gaskets, note all the screw settings and replace the orings, etc. then you did not rebuild it.
you dont know what you dont know, I am still learning too. usually about 1 ski a year just totally hands my azz to me. lol
and I hate life while I try and understand why. The information learned after doing battle with that issue is priceless. you cant get it from a book and nobody can teach it to you. you just have to suffer thru it.
I may be totally off base but if you dont have those carbs thoroughly gone thru then how can you know for sure the prob is not there? another thing that can bite you is the little chrome lever has a bit of a nub on the sides of it and sometimes the needle can get hung up and will just pour fuel. but that is pretty extreme and usually runs awful if it all. and when you take it apart you can see it stuck open.
again please forgive me if I have overstepped but I am just trying to help a fellow rider and anybody else who may want to rebuild thier carbs.
im not knocking you, I started out the same way. but over time you run into these issues and have to dig deeper into the problem. eventually its just about being thorough to save time and money.
the checkvalve rubber is a piece of cake.
put the disk on the body
put the rubber on the disk
take a small flat screwdriver, mine is like 1/8 or 3/16 wide tip, press down on the rubber with finger or thumb and use flat head to push some of the rubber thru( the outside lip is what you want to push thru not at the center).
while keeping pressure on disk flip body over and use flat head to pry lip of the rubber you pressed thru. pry from the outside towards the center.
keep working around until the whole nipple is in.
takes 5 seconds.