Throttle Balancing

I balanced the throttle bodies on my K6 yesterday using a home made manometer with engine oil in the pipes (figuring this will at least burn off if ingested).


To begin with there was several inches difference between the height each side, eventually I settled on a figure within an inch of each other. My rear cylinder was 'dragging' and the idle speed increased when balanced, so I had to counteract this with the idle adjustment. The balance adjuster is incredibly sensitive, in total I've only turned the screw 1/8" of a turn. I rechecked the TPS adjustment and found the line moving up just off idle.


The 'surge' coming off the overrun back onto the throttle is much reduced and the bike now cruises smoothly 500revs lower than before.


Before I started I ran some approximate calculations and found that the linkage rod will grow 0.1mm due to thermal expansion over it's length with a temperature increase of 50C. What this really means is that there is a limit as to how accurately you can balance them, but it's worth taking the time to let the bike sit idling long enough for the throttle linkage to warm through.

[Bibio]

0.1mm is going to make shizz all difference in the grand scheme of things, there will be more play than that just in the universal joints.

as long as both levels on the manometer are equal at tickover then thats all that matters.

as for the tps, its exactly what it says Throttle Position Sensor. it tells the brain where the throttle position is so moving just off idle is perfect. once the TPS is set correctly you should get a lot smoother (less engine braking) throttle for slow manoeuvrers such as mini roundabouts, makes fekall difference at higher revs and only comes into play when you shut/open the throttle.

Originally Posted by Bibio

0.1mm is going to make shizz all difference in the grand scheme of things, there will be more play than that just in the universal joints.

Agreed that there is more play than that, but the spring in the rear throttle body prevents that play from actually being part of the system, if the rear TB wasn't sprung then the play would be relevant. I'm very lucky in the fact that my bike's only done 2.5K and whilst I've no experience what effect mileage has or what a typical amount of adjustment might be, but given that an 1/8th of a turn on a thread with 0.8mm pitch has made a difference, the growth shouldn't be discounted.

[ophic]

Wouldn't everything else heat up and expand at approximately the same rate as the engine gets warm? Thereby making the expansion irrelevant?

Originally Posted by ophic

Wouldn't everything else heat up and expand at approximately the same rate as the engine gets warm? Thereby making the expansion irrelevant?

That's not so easy to calculate! My general point is that things move when they warm up so give everything a chance to warm through before settling on the final balance setting.