Sorry to hijack the thread,but you're saying that if the vent lines are blocked, it could cause the float not to rise all the way and let fuel continue to flow into(and up above) the bowl? I also have an `81 650 that has had me stumped with an overflowing #4 since last fall. My fuel level will rise until it pretty much reaches the tank on my tubing connected to the drain. I've tried all the other suggestions here that I've found(polishing the seat, swapping floats and float needles, etc) with no luck. I even tried modifying an old Mikuni brass float I had laying around to see if that would work. If I removed my tee from in between 3&4 and there was no blockage, fuel should flow out of here before it rises high enough to spill out from the airbox side of the carb, yes? and if I can get a carb cleaner nozzle up into where the T enters carb 4, would it come out into the bowl if everything was clear?
Again, sorry to hijack, but this has been making me bang my head against the wall since last summer/fall!
Those lines with the tees are bowl vent lines and must have the tees installed, otherwise your just 'venting' one carb into the next ( closed circuit , no vent ) and the pressure in the bowls would hold the floats from rising all the way, i.e. overflow....... the vent hoses from the tees I think go up to / or over the airbox....maybe someone else can confirm that. Good luck.
And this is the real answer.
If you will leave those opening without those tees it would work too, only overflow would drip at the engine directly. Fastest trick is to connect to each carb a separate tube and put them somewhere "out of the way".
