Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > Sport Touring: ST4 / ST3 / ST2 > ST4s idle settings

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Problem setting ST4s fuelling – any help will be appreciated.

Bike is 2001 ST4s, 22000 miles, recently serviced, generally running well, but it has never gone as well as my S4r monster did (both totally standard inc 15t front sprockets). Recently I’ve bought a 996 SBK and the ST is nowhere near as quick (The 996 does have a 14t sprocket fitted). I can squeeze 200 miles from a tank and still have a bit left, so it may be a bit too rich but its not extremely so.

I’ve been following instructions on Brad Black’s website, and have also read the Ducati factory manual and the Desmotimes book – all follow almost identical procedures.

This morning I’ve:
set the TPS to 150mv
screwed the air bleeds fully in
run the engine up to temperature and balanced the throttles using only the balance bar in the throttle linkage – vacuums are now balanced between idle and 5000rpm so I’ve left the air bleeds fully in
set the idle to 1200rpm
connect Technoresearch software and Gunson Gas Tester

Idle trimmer had been set to +15.

At this point I was planning to use the Technoresearch software to set 3-4% CO, but having stepped between zero and +40 on the idle trimmer, I cannot get the CO to rise above 1%.

I’m using the exhaust sensing screw in the rear downpipe (not the tailpipe exit).

Can anyone please suggest why I may not be able to get above 1% CO?
What sort of trimmer values are typical for a standard bike?

My gut feeling is that it’s running rich – my MTS1000 has an idle trimmer value of –3 (set by the local Ducati dealer) and is the crispest, sharpest bike I’ve ever ridden. I know that you cannot copy the value from another bike and expect it to be right, but I would expect Ducati to design the ECU so that your base line value should be zero and with a standard bike I wouldn’t expect to be far from that, and the MTS bears this out. However the gas analyser does not agree with my diagnosis.

I did suspect the gas analyser was faulty, but a quick test on a friends badly running carb 900, showed readings from 8-10% CO, so the analyser isn’t dead.

Any suggestions as to why I can’t increase the CO reading or what I should set the trimmer to would be appreciated.

Many thanks, Mark.