Ducati 98 916 bad throttle response below 2000 rpm when warm - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 13 (permalink) Old Apr 20th, 2016, 11:39 am Thread Starter
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Ducati 98 916 bad throttle response below 2000 rpm when warm

Hi all,

I've finished my renovation project based on a 98 916biposto.
I have lately noticed that the bike has a bad throttle response when warm below 2000 rpm. Typically when i give a short throttle pulse (like when shifting gear down) the response is lagy, sometimes it rattles. When idle is above 1500 rpm all works well..

I am suspecting the bike to run rich. At startup all fine, i guess some sort of starter is applied maybe this is not deactivated while warm..

I fitted back the original exhaust and EEPROM after the renovation and do not know exactly the history of the bike. It looks like a custom EEPROM + exhaust and line was installed before. It could be that they dialed the richness pot previously.

Do you have a clue what are these symptoms and how to fix it ?

Thanks for the thoughts ;-)
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post #2 of 13 (permalink) Old Apr 20th, 2016, 12:48 pm
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The later year 916 has a trimming potentiometer inside the ECU for use in adjusting the CO level. A V-twin will idle very poorly if the CO is set below 1% – a typical CO figure for smooth idle/running is 4% to 6%.

The fuel entering the engine is controlled by the injectors, principally by how long they are open for each engine cycle. Typically at idle they are open from about 1 ms to about 2 ms. The CO trimmer affects this duration. This change is the same for both cylinders, and cannot affect the CO cylinder balance.

1.6M ECU CO Adjustment

On 1.6M ECUs, the trimmer is located inside the ECU and the rubber bung must be removed for access. Reseal the rubber bung with waterproof/duct tape after you have finished adjusting the CO.

There's a small 1/4-inch square trimmer potentiometer positioned next to the Eprom socket. The potentiometer has a range of about 3/4 turn, or 270 degrees. When you turn the trim adjustment clockwise, the mixture is leaned.

To place it at the default position, simply set the trimmer in it's mid-rotation point. When you hit the end in either direction – STOP – there is no roll-over on these trimmers and they will break if you try to force them beyond these points.

You should adjust the trimmer to obtain 4% CO using an exhaust gas analyzer. Without an analyzer, here is a procedure, complements of Brad Black.

Starting at the midpoint:

1) Turn the potentiometer counter-clockwise until the engine stumbles. Remember this position – rich end.

2) Turn the potentiometer clockwise until the engine again stumbles. Remember this position – lean end.

Turn the trimmer back (counter-clockwise) from the lean end stumble point to a point 1/3 of the rotation needed to reach the rich end stumble point.

This usually ends up at about 4% CO. Again, best power is realized when full-throttle CO is in the 4—6% range.

If you don't get a stumble point, there's not much you can do. Wind the air bleeds in if there's no rich stumble point, out if there's no lean stumble point.
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post #3 of 13 (permalink) Old Apr 20th, 2016, 3:35 pm
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Good post above for working towards a decent baseline set up, but the larger issue in my mind is the fact these bikes don't like to live 2000 RPM or below while riding. You're going to lug the engine and there is little usable power there. 3500 to 5500 RPM is a much happier place to be when tooling around on a Duc, especially a 4V Desmoquattro variant.

When I have a good tune on the bike, I can plunk through a small town main street 25 MPH zone at around 2000 to 2500 RPM on level ground, wind at my back and NO expectation of decent power should I need to accelerate. It can be done, just not a good idea.
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post #4 of 13 (permalink) Old Apr 20th, 2016, 3:39 pm Thread Starter
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Thanks Shazaam, very good information.
I will give it a go and see if I can correct it..
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post #5 of 13 (permalink) Old Apr 20th, 2016, 3:50 pm Thread Starter
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SS904, I am currently quite satisfied about the low rev rideability. I have rarely backfire, though it can happen (setting the richness might solve this too) You're right saying that the twin doesn't live under 4000 rpm. My problem in that case is really only in case of blipping the throttle from near idle. It makes the hole thing somehow not very reproducible on shifting down on a normal ride. Driving more aggressively solves the problem as revs don't drop near idle.. :-)
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post #6 of 13 (permalink) Old Apr 21st, 2016, 3:38 am
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Agree with the CO setting, best to get a meter though to measure it but, also make sure the TPS setting is correct before you start.

Mine pulls cleanly & smoothly from idle to the limiter and although it has been custom mapped for extra power/smoothness, it was pretty good before.

916, M900 & Guzzi LeMans II
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post #7 of 13 (permalink) Old Apr 21st, 2016, 8:24 am
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Some chips were also fat down low so they would feel lazy on the throttle. The difference from an FIM megazone or ultimap to a Ferracci or Ducati performance was most noticeable at low revs and when blipping the throttle when in neutral. The FIM chips were always much more crisp even in stock form though they were tuneable as well. Ferracci and DP chips often made the same power but were richer and felt lazy because of it.
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post #8 of 13 (permalink) Old Apr 21st, 2016, 12:03 pm
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All 916 have a trim pot, its either a P8 ecu(SP and strada) or a 1.6 ecu(rest), both will have a pot for adjustment.
Theyre quite sensitive so you need to have a CO meter to measure, or if you done it a few times its ok without, it will idle higher and sound right when in the sweetspot. Tuning basics, nothing special.

Last edited by TomTom; Apr 21st, 2016 at 12:11 pm.
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post #9 of 13 (permalink) Old Apr 23rd, 2016, 3:47 pm
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That was a really great post. I'm having the same issue after fitting an upgraded air box seal. Makes no sense to me at all. She was running sweet before I fitted it and now at low rpm she's a bag of cats. She almost feels like she's now running lean but fitting a proper seal to air box should in theory have her running richer?
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post #10 of 13 (permalink) Old Sep 17th, 2016, 12:59 pm Thread Starter
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Hi all,

I've been very busy lately but I managed to try the tests like Shazaam was suggesting.
Result :

First, I do not manage to stumble the engine on the rich side of the potentiometer. On the lean side I found the the stumble point. Why that ?
I warmed the bike (when cold the throttle response is spot on..) confirmed the bad throttle response (blipping from idle) and tested various potentiometer settings.
On the rich side i got backfires what probably indicates too rich but still the same lagy response. I didn't find a position where the throttle response was like when the bike was cold, this up to the lean side.
I kind of "heard" an optimal setting where the engine idles cleanly and that was the original setting I had..

An idea what the problem could be ? I don't get it as everything is now original. But the previous owner had a full race Sil line with ultimap chip. I have the original EEPROM now, maybe they have been touching more than just the richness pot...maybe carb/injector settings...

Expert help welcome ;-) !

The bike is very much ridable because while riding it rarely drops to idle, it is not dramatic but this still bugs me, for sure it is not normal.
The little blipp at the red light is most often a failure (needs to be fixed, it's a ducati not a mopped !!!)
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