Hi folks

my 907 just idles a bit to fast when at normal temp, at 1500-1750 rpm. Want to adjust it to 1250 rpm. How? found the following in the 907 shop manual. But they do not explain how to proceed for a good adjustment. Just fiddling around?
thanks George

George,

the Bowden cable screws are like idle mix screws on a carburetor..they only let air in to the manifolds (one for each).
you could stuff around with them and the idle mix potentiometer on the ECU and get a reduced RPM result... but that might also be a flat spot between idle mix and open throttle (not desirable).

assuming the idle mix is correct now (and has been set with a CO meter) it's probably best to leave them alone.

the place to set the idle is at the main throttle cable connection; balance both butterflies (preferably with vacuum gauges) then set the idle screw. You should do the whole "tune and TPS set up"...but might be lucky and get the lower revs just with the screw adjust..
it's a shit of a job because you need to prop up the tank to do the screw adjusts and run the bike; maybe your fuel lines are long enough??

an anomaly I found was that my nicely balanced idle vacuum went 10 - 15% out-of-whack at 4000 RPM on open throttles...which is where I prefer to have the tune "right" ...grrr.. so my idle was re-set a little off balance - and I left it around 1200 - 1400 so it wasn't lumpy...
I suppose it's up to the individual where you want the bike running smooth and how much idling you do; mine gets mainly highway use so I don't care about lower revs too much.

Note: don't let the screw off too much so as to allow the butterflies close fully in the throttle bodies!! They will stick and make throttle control and acceleration jerky when they let go.

Laddie is right. You can do the whole TPS adjust, then balance the throttle bodies, then the air screws, then the CPU screw if you have something to stick up the pipe and read the CO2.
However, to just adjust the idle "speed" the set screws are your best bet, . . . . however . . . . . there are two, one at each throttle body. The one on the right is not accessible unless you take the gas tank off, then the air box. Last time I had mine apart I drilled an access hole from inside the air box so that I could get to it ONLY after taking of the the tank and top of the air box.
The thing to do is get on the left side of the bike on your knees. Look from the front just beneath the radiator and look for the throttle linkage that the choke cable and throttle cable connect to. You will see the left side throttle body idle set screw that you can adjust with a long screw driver or a 6 or 7 mm socket on a long extension. This will open both throttle body butterflies to set your idle. Adjusting the one set screw just means the other non-accessible set screw doesn't touch the stop on that side any more.
Good luck.
du907

Thanks du907, that makes life simpler. Will try it in comming days. But still wonder what the function is of the 2 "by-pass" screws in the picture?

Hi Du907,

Went on my knees in front of my Duc. What an experience!

But could only see the cylinder head of the horizontal cylinder. No cables or throttle screw whatsoever. Have to remove any fairing?

g.m.c.janssen

You are going to have to bend over a little more! Probably lay on your back and look up to see the screw. Check out the enclosed photo with the red arrow pointing to the screw. Sorry, best picture I could get. You can do it. I use a small rachet with extension, then a u-joint adapter, then the socket.
Good luck

Dunno if this is applicable to the 907 as I,ve never seen one up close but , For poxy to get at screws on carbs ect I have cut the socket bit off a suitable sized cap screw and soldered/ welded it to the head of the afore mentioned poxy screw ( carb ballancing screw on the SS ) and then use a very long ( home modified ) ball end allen key, this way I can approch from an angle and the ball end is a lot easier to keep in the socket, especially with a magnetic tip . Paint the screw head dayglo or white. If you tune your own bike these wee tools will save you a lot more time than it takes to make them