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Hey, what are you guys who are using Mikuni VM30's on non-race bikes doing with all those little puke tubes that are coming out of the carbs? i can't see how you would do an aesthetically pleasing job of running them all to a suitable drop zone, and leaving them all sticking out wherever like an old man's eyebrows doesn't seem great either... can i just pull them off and leave the li'l brass outlets? do they spew a lot? Any advice appreciated!
I've been running VM30's for a year and have never seen a drop of gas come out of any of the drain tubes. If you don't like them I'd say yank them off............................
I had all the short red tubes for a while and it puked gas all over the engine messing up my paint. I used some small diameter black fuel line and a bunch of T's to connect them all together and run them down where my breather dumps under the engine.
greaaaat.... gotta love it when the answers are in conflict... Not that I'm not appreciative of the response guys! Any input is appreciated, I'm just not quite sure what to do with the information...
They are needed and at a specific length
Pulses in the intake makes fuel move and act as a 'pump'
If you have high humidity, air gets sucked in and out at varying rpm and you will get water in float bowls from condensation.
Yamaha ended up with a recall on various bikes in the 80's because lines were too short and exacerbated the problem
They are needed and at a specific length
Pulses in the intake makes fuel move and act as a 'pump'
If you have high humidity, air gets sucked in and out at varying rpm and you will get water in float bowls from condensation.
Yamaha ended up with a recall on various bikes in the 80's because lines were too short and exacerbated the problem
Ah, so they're tuning breathers not puke tubes... so given normal humidity and the fact that with my lack of skillz the carbs won't be tuned right anyway i can just leave them off and all i'll do is compromise my performance? and buddy that had gas leaks was seeing a symptom of a different problem?
Sort of. They are breather tubes, but as PJ mentioned, if they are the wrong length you CAN end up with some detrimental harmonics in the tubes. I tend to leave the short tubes on, but if the bike has a tendency to weep fuel from time to time, I'd run longer tubes. For example on a bike with steeply angled carbs they can weep under hard braking.
What I would do is to fit long clear or black tubes and hang them together with cable ties and take them somewhere safe to discharge. Mine go into a breather bottle on track bikes and under the engine - and away from the rear tire on street bikes.
So if they're a tuned length then either removing them for aesthetics OR lengthening them to a puke tank is going to compromise performance... So I might as well take them off to make it pretty and see how much gas it coughs up and if it's too much I'll re-plumb it away from the action... Sound ok?
ah, ok... so not that the stock tubes are a perfect length, just that they're not a problem at that length! so remove, shorten or lengthen at my own peril and revisit later?
More or less. I have never had an issue with short long or missing tubes. They are an issue if they are connected to each other and don't vent though. ...
If they puke gas you have done something severely wrong (except in conditions noted)
They should be just breathers but, they do 'pulse'.
It's not guaranteed carbs will have problems with wrong length or removed
Yamaha obviously thought there was enough possibility, hence the recall
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