Posted: Sat Jul 27, 2013 7:20 pm
nab 301 wrote:All of the above is correct to a certain extent. You've got to the stage where you need to hook up the gauges of your choice , twiddle a few screws and adjust cable adjusters and actually see and hear what differences they make.
At idle you need the throttle cables and fast idle cable to be just slack enough to allow the throttle bodies to be fully closed.
Idle speed is controlled by the the air bypass ( brass) screws. If the bike is running reasonably ok you will probably only need less than 1/16 of a turn on one side to balance and keep the idle speed in spec. If however (depends on the bike ) when you balance it at idle, the idle speed is incorrect, you'll have to adjust both brass screws equally to increase /decrease the idle speed . (it's also unlikely both screws will remain in identical positions) (Sometimes it helps to remove the screws and clean out the orifices with carb cleaner if there's a problem balancing) That's the easy bit...
When you open the throttle , the primary cable is linked to a junction box which splits into two cables, one for each TB. This is where all the innacuracy can develop. Basically you're attempting to synchronise these cables while also compensating for any mechanical imbalance between the cylinders at 3 to 4 k rpm (using the vacuum gauges to show what's going on). If and when you get to check yours , you'll figure out quickly enough that minute adjustments only are needed which is why adjusting one side only can simplify things. (Without stating the obvious for example , if the left tb is opening early as indicated by the gauges , you can tighten the right hand cable or loosen the left hand , it doesn't matter , once the cables aren't holding the tb's open at idle)
This is where you need all the outer cables to be seating correctly and the cable adjusters to be lubed and corrosion free , and in extreme cases to clean the cable quadrants, because any dust /grit imbedded here can affect the balancing .
Again, one cable is all you really need to adjust, but as you found out by researching, tightening the cable locknut can affect the readings dramatically.
With time, you'll learn how to compensate when tightening the lock nut.(it's just something you'll get a feel for)
On a low mileage garaged bike this is all generally easy enough , it's when you get to 100k miles with worn tb's , valve guides etc that the fun starts#
Alternatively if the bike appears to be ok , just ride it and ignore all of the above ramblings....
Nice write up ned. Done mine today using a Carbtune and its easy enough with practise. As you say when tightening the locking nuts on the throttle body cables the cable adjuster tends to want to move as well...long nose pliers were my cure. On test the bike does feel a little smoother particularly going from off to on the throttle.
Nice one
