[Sportyeric]

My bike jerks at 30 mph, which I believe is a result of running too lean. It has been worse since the most recent tune-up. I suspect the tune up was geared to max power rather than drivability. I could just take it back to the mechanic but there are some practicality issues with that. (Its 3 hours travel.) So the question (hoping not to sound really dumb): can the low-speed mixture be adjusted with some adjustment screw or is it all done digitally?

 

[Johnny]

To answer your question both.

My Dealer tells me the ST is a bag of springs, get it right in one place and it is bad elsewhere in the rev band.
The adjustment on a 2002 ST4s is electronic so you need something like Tuneecu or similar. You shall need the connections too. It’s not straightforward as the TPS needs to be done, then balance , then tick over then CO/Fuel.

The manual part is with the air bypass screws which set tick over CO (to some degree)
You could experiment with a quarter turn in of these but remember where you started. I made a file which I shall try to attach

 

[Johnny]

File attached

 

[Sportyeric]

Thanks, Johnny. That is a brilliant piece of prose. best written Ducati tech article I have seen since I bought this bike. Thank you.

 

[Johnny]

Thanks, Johnny. That is a brilliant piece of prose. best written Ducati tech article I have seen since I bought this bike. Thank you.

Er..Thanks I went back and read the thing again. It is a cut and shut from other peoples work but I added bits and bobs. I could not use cutters to remove the throtle link and recommend not trying

 

[belter]

That attached article is pretty funny in places - it tells you not to do something, then tells you to do it. It’s no wonder people have issues with them. St4s is not a bag of springs, they’re pretty straightforward if you do it right.

 

[Johnny]

That attached article is pretty funny in places - it tells you not to do something, then tells you to do it. It’s no wonder people have issues with them. St4s is not a bag of springs, they’re pretty straightforward if you do it right.

Ok Belter, point out some of the contradictions and I shall modify it

 

[belter]

When I get near a laptop I will.

 

[belter]

at the top of page 4 your piece (taken from my original post here: BikeBoy.org - Ducati 4V Desmoquattro Non Linear TPS Baseline Adjustment (plus ST3)) has:

> Open and close the throttle a few times to check the idle setting is stable and adjust if required. The TPS is now set and the horizontal throttle body
>stop screw (7) should not be touched again

then on page 5 you have (possibly from the old FIM write up?):

>Adjust the IDLE RPM. Set the idle rpm at the manufacturer's figure by adjusting the throttle butterfly stop screw (or screws). We >recommend 1200=1500 rpm.

once you set the throttle opening with the idle stop screw you don't adjust it again to make it idle. that's what the air bleeds are for. you set the air bleeds to give you the idle speed, then you use the gas analyser to check the idle mixture which you adjust via the diagnostic tool and finely adjust via the air bleeds to make both cylinders the same.