Balance tube

[inanecathode]

I can't remember if i posted about it or not, but i forgot i put a balance tube on my bike. Goes between the two yikes ports, no restrictors or anything. The initial idea was "hmm well, hose doesnt crack as fast as these stupid caps (ended up cracking in kingman of all places heh).
What happened was, the idle went crazy high, obviously theres less restriction having each cylinder pulling idle mix fromt two idle jets instead of one. So i had to adjust the idle stop waaay waaay down, barely touching. Cool. The other thing that happened was the idle got lumpy. Not lumpy like bad, but it goes kinda pa-dump-pa-dump-pa. The benefits i've seen are pretty cool though, extreeeeeemely stable idle. I havent heard it misfire a single time since. Very quick return to idle. You rev it, it goes up, you let go and it goes RIGHT back down. It also has smoothed out performance across the band. My weird wide open throttle high load stumbling went away, and my part throttle stumbling went away too.
The only real downside i've noticed so far is after really really high load high speed wide open throttle (the other day, going up a hill on the interstate, 5th gear, wide freakin open, going about 80 and slowing down after about 5 minutes of it) it starts to starve of fuel, probably because of the lack of vacuum. A quick turn to prime fixes it.

Not saying it's the ultimate fix or anything, but it's been a pretty neat bandaid for some problems i've had.

[fret not]

Sounds like diminished fuel flow.  Either that or you are sucking gas faster than it can flow into the carbs. 

     fuel cap breathing restricted
     failing diaphragm(s) in the pump/regulator
     leaking vacuum line
     gremlins

[inanecathode]

Eh well, i suspect it's a lack of adequate vacuum to the petcock. I know the petcock leaks when the bike is off, so it must be a bit crispy. Probably the crispiness in addition to the balance tube reducing vaccum at high throttle openings for long periods causes the petcock to shut off long enough to start starving the carbs of fuel. When i said its minor, i mean i can barely tell its doing it after a loooooong time, not a huge problem yet. More concerned with it not closing when the bike is off, anymore it just leaks and leaks and leaks.

[fret not]

You could do something about that.

So, you are saying you have a tube connecting the YUCKS ports on the cylinders, hooked together?  One tube?

[Lucky]

I trird this & my experience was that the 'balance tube' screwed up the pulses between the intakes.  I could detune it to make it better, but the bike has a lot more power with the YICS sealed & hooked up, or even just blocked off...

[inanecathode]

You could do something about that.

So, you are saying you have a tube connecting the YUCKS ports on the cylinders, hooked together?  One tube?

Yup, just one tube, not even using clamps  !

Lucky: I dont see how you could tell if the intake pulses are screwed up or not. Mine runs better with the balance tube (after backing the idle off, obviously). Than it ever did with any combination of yikes port messing arounds. I dont see how we could have such opposite results with either one of us actually being right. Same for the whole yics thing itself, i dont see how it can do anything really with such wildly varying results.

But the balance tube does make it idle cool, for what it's worth. That, and the tube doesnt crack or break. i dont think i've had a hose itself actually leak on any kind of engine that i can remember, its always been a gasket or a fitting, or the hose gets so hard it breaks when you try to take it off.

[Lucky]

Not sure which exhaust you have, I've got Macs, so you can pretty much tell what each cyl is doing independantly.  they were just all over the place....

[inanecathode]

Not sure which exhaust you have, I've got Macs, so you can pretty much tell what each cyl is doing independantly.  they were just all over the place....

Heh, sweet. Makes sense the pulses at idle would be different, vtwin having a firing sequence not 180 degrees out like virtually every other vehicle.
Does even out the mixture though, drawing from two carbs one a bit more than the other.