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.
The bulk of what you've done is spot on. The CO trimmer, as you said, can be anything. Zero is a good place to start. Now you've balanced it mechanically, with the balance bar, i'd give the air bleeds 1/4 to 1/2 turn out. You can check the balance stays good, but it's not now essential. You are looking for equal CO for both cylinders. You can give up vacuum balance to attain this. If the CO is the same then the cylinders are producing the same energy...... You need to sample both cylinders, not just the one. On like for like settings, air bleed and trim, the rear is usually richer. Tbh, i would suspect the analyser to some degree. They do the job, but barely. Reaction and sampling times are pretty slow and accuracy is quite low. I've set bikes up that have been done with them and they've been way off..... Just re read your post...... did you set the TPS with the throttle stop back off, cable disconnected and balance bar backed up to make sure front throttle is fully closed??
I haven't got the ST4S TPS value to hand but the 996 value should be 423mv or 2.58 degrees, the 150mv is only the base setting with butterflys closed??
I thought setting the TPS with the throttles completely shut was the way to go, then use the throttle stop to hold the butterflys open the correct amount for the idle speed once the trimmer and air bleeds are set.
I thought setting the TPS with the throttles completely shut was the way to go, then use the throttle stop to hold the butterflys open the correct amount for the idle speed once the trimmer and air bleeds are set.
Yep. That's the way. The idle values are fairly ambiguous tbh, as more air bleed and fuel trim would need less throttle stop and hence a lower mV output. Useful for checking but the closed set with 150mV is the way to go.
UPDATE - Yesterday I reset the TPS using the tenhoresearch software (I'm not sure whether this has made a difference as the ST4s has a manually adjustable TPS, but I was advised to do it on other forums. I've also made the mixture 5 points richer and now the bike pulls much better with an improved throttle response.
The idle is still a bit rough - a touch too fast yet occasionally stalling, but once the throttle is open its much improved. I'll tinker with the idle over the next few days and post an update, but for now its what I wanted (at least once you're moving).
Thanks to everyone who posted advice. Cheers, Mark
The ST4 uses the non linear TPS. You can't reset it in software. That function is for the linear TPS used on 749/999 etc. It's a function that shows up in VDST because of the 5.9 ECU being used. The extra click on the mixture have probably given you the improved running. The TPS reset could/will have thrown it out. Only way to set it is with closed butterflys and the 150mV setting.
30-Jun-2009, 12:28 
Linear Mode
