Throttle Body Balancing - end stop position on idle?

julian · Post by **julian** » Mon Mar 12, 2007 3:00 pm

Gents - when balancing the throttle bodies, at the idle setting (i.e. no throttle) should the throttle body mechanism be resting on the end stops (and the air requirements being handled purely by the brass air bypass screws)?

With tank and fairing off yesterday I noticed that I have a few mm gap between both the LH and RH throttle body mechanisms and their respective end stops

Cheers

johnl · Post by **johnl** » Mon Mar 12, 2007 5:37 pm

yes, I blieve so. I set my brass screws to 1 1/2 turns out from seated and then turned the left brass screw to balance the throttle bodies. I then used the cable adjustment on the right throttle body to balance them at higher revs.

with hindsight i think i should have only taken them out 1 1/4 turns as the tickover is a little high ( 1300rpm ). That'll be this weekends little job then.

folks, please feel free to correct me

r550s · Post by **r550s** » Mon Mar 12, 2007 7:54 pm

the cable quadrants should rest against the stops on closed throttle (with no choke on!) If they're a couple of mm off as you say, then things are amiss - either your cables haven't got any slack in them (in which case you'd have a tickover of a zillion rpm), or somebody has tinkered and backed off the stop screws - (check for the blue-coloured paint that should be on the threads of the stop screws.) These should be set so that the throttle plates are fully shut in the bores, when the quadrants are against the stop screws. The tickover can then be entirely controlled by the brass bypass screws. That's the theory, what happens is that the brass shafts wear in the throttle bodies (especially on the RH for some reason) and, whilst this isn't a major problem - apart from the rattling on tickover, it does mean that the tickover setting doesn't seem to respond to the brass bypass screws as it should - you should be able to stall the engine by screwing a bypass screw in. Ths is because air is leaking around the closed throttle plate, because the wear on its shaft means that it doesn't sit properly in the bore anymore. Now, if you were to try and remedy this - you might be tempted to back off the stop screws. This would mean that throttle plate would spring shut to the point where it jammed itself in the bore a little bit. It might seem to work, but you'd end up with much more wear.

winger · Post by **winger** » Tue Mar 13, 2007 7:37 am

Hi Jules

Out of interest you say throttle bodies,i've only ever balanced one,all i've ever done is balanced the right to the left,i've never touched the left side in 7 years.

julian · Post by **julian** » Wed Mar 14, 2007 2:12 pm

OK, thks.

I backed the cables off so the quadrants just hit the stops. It got dark so I need to fine tune, however the engine feels much better and runs smoother now.

It's a lot easier to see what's going on and make adjustments without the fairings and better still without the tank - although the bike obviously won't run.

I've been using a Morgan CarbTune for 5 years and think it's time for a Twinmax as the MCT needs to be hit with a spanner to get a correct settled reading after each rise in revs.