Sasha, I wish I was there to see things. Can you take the carb off and do a video chat with it and a couple screw drivers? Just like he was saying. It really sounds like the idle jet is clogged or the passage is restricted. It's the smaller jet. You should be able to look through the hole in the middle of the screw driver slow and see light on the other side. Also Carb cleaner with a little tube should squirt cleaner through the passages to the openings. If you can't see though it, Poke it through with a single bristle from a wire brush. Gently! Might need to boil it for awhile in vinegar or lemon juice as an acid to help clean it out. I'm still down for the VIDEO CHAT CARB On SCREEN!! The one things in theory as to why the choke has to be on is it's not getting enough fuel and the choking of the system is causing the venturi to suck the nessary fuel from the main jet I would think. As far as the air breather being needed to restrict air flow, If I had an air cleaner that caused that much restriction I would take it off. They clean air not tune engines. I've been runningmy 1966 Dream 305 for the past couple week with no breather on it. *ASHAMED TO SAY SO!* Runs fine and starts with less then a half revolution on the starter.
Another theory on your Bike is the float level is so LOW that the choke is creating a suction strong enough to pull the fuel through the fueline. But It dosn't explain the higher revving unless maybe the idle set screw isn't just right. So many veriables! Always best to see what's really going on. Maybe do a video of it when you take it apart and inspect everything? I would help with the carb settings and checking via video chat on yahoo etc. I just did mine. Ended up being a reamed out pilot jet. But My Plugs were Silted like crazy! Thought it was a spark issue at first but it was just an extreme case of bad Air:Fuel Mix. But I had to go thorugh the whole carb a few times to figure it out. Too compareing the new idel get with the one I was using to get the ah HA Moment! Is that a stack carberator for the 305? a PW-22 carberator?
Would also like to see the plugs, if they are very clean, it's porbably to much air.
It could also be a combination of many things. A good video of things would get you alot of AH! HA'S! =-)
She dies when I open the choke!Brewsky hit the nail on the head. Missing air filters will change jetting because there is a pressure drop across any filter.
As he pointed out, the probably cause is a blocked slow (pilot) jet or the drillings above that jet. I'd take that carb off and clean it thoroughly and get a replacement filter while you are at it. And then set the float level.
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