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Old March 5th, 2020, 06:29 PM   #1
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1098 Vertical Cylinder Cold

Insearch of why the vertical cylinder was cold and fouling plugs, I pulled the airbox. I thought the correct way to set up the butterflies was to use the tie rod. Then I found the adjuster on the H - Throttle body. After screwing around with shims and drill bits to check the gap in the butterflies I started moving that adjuster. to my surprise only the drill bit in the v-butterfly fell out.
The adjuster is not an idle setting like I thought. It sets a bias towards one or the other cylinder. Turning clockwise opens the v-cylinder starting point and does not move the H butterfly at all.

After putting it all back together I started the bike.
Fist exhaust temps were about 150 degrees colder on v. Turned the adjuster three full turns to right rpm rose to 2000 but then went right back to 1200 on its own. The initial change made the idle exhaust temperature go from 325 to 577. The front remained 425.

After a little tweaking I was able to use this bias screw and the air bleed screws to make both exhaust manifolds read more or less the same based on where you took the temp.

Now when the bike starts it runs up to 2000 rpm for a short time, drops to 1200 and exhaust temps are proportional.

Obviously the bike rides great. The throttle is sharp. No more stalls at stop signs.

I am calling this adjustment "Bias". To my knowledge it is not referenced in the manual because the entire TBI assembly is not serviceable. At no point have I had to do a TPS reset. I think the ECU and the Idle servo take over and set the idle speed.

This may not be news to you. But I have talked with every mechanic I can find and all agreed the rear cylinder was shot if it was not the valves, It surly was the rings.

Now maybe there is a difference in wear front to rear. But turning a screw and seeing that cylinder run hotter and colder with adjustment on an injected engine tells me the fuel comes straight out of the map. With the Race ECU and no O2 sensors we know that is right. This Bias screw or Balance adjustment will get the colder cylinder running hotter and closer to correct Stoichiometry.

People with more experience than me chime in. Is this adjustment part of the Multi thousand dollar Ducati Service Software? Am I just late to the party?

The adjuster is the slotted 8mm bolt on the side of the butterfly rod on the horizontal cylinder. See Picture...
Attachment 169323
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2007 Ducati 1098
2003 Harley Cafe Racer
1956 BSA DB33 Clubman

Last edited by parrish37; March 6th, 2020 at 08:02 AM.
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Old March 6th, 2020, 01:01 AM   #2

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Join Date: Sep 2013
Location: Athens - Greece
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i had an issue like that for 3-4 months, changing vertical spark plugs all the time, weird idle rpm, bike not holding rpm when i pulled the clutch in motion and motor turning off...

i left it 3 weeks at a dealer, he said he adjusted a vacuum on the vertical but i am unsure of what he did, the bike ever since works perfect like you describe.
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Old March 6th, 2020, 07:59 AM   #3
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When I first started troubleshooting the problem I had exactly what you just described with yours.

My first attempt at a change was to open the airbleed screws. That helped a lot and if I had not kept taking temperatures of the exhaust and still had 150 degrees difference all the time. I may not have chased down this Bias or balance adjustment.

Please do not berate me for arbitrarily moving the sacred air screws without a manometer. It did finely lead to fixing my problem.
2007 Ducati 1098
2003 Harley Cafe Racer
1956 BSA DB33 Clubman
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