Persistent left cylinder misfire

[Tom in Virginia]

On 7/10/2021 at 9:48 PM, docc said:

Yeah, like,

"Hey, hey, bud - gotch'yer relays rat'chere. Need a sprang?

You needs a sprang. Gotcha covered, bud . . ."

Oh if only all V11 owners knew how much conversation (and ingenuity become reality) those springs have generated.

[po18guy]

28 minutes ago, Tom in Virginia said:

Oh if only all V11 owners knew how much conversation (and ingenuity become reality) those springs have generated.

And to think that the springs were given so little thought back in Mandello. But - that's exactly why we are having this talk! The one thing they should have copied from Ducati is a desmo shift mechanism. 

[Beemrguzt]

So I am a new V11 Sport owner and would like some opinions on something. I of course have that weird left side hiccup at low idle rpms. Ive been trying to get my hands on a set of vacuum ports to screw in to my manifold to do the balancing. Pretty hard to come by. Anyone have a "buy now" source for these ports? So heres my theory, since i have a differential manometer but no ports to attach it to Ive been going over just about everything on the bike while I wait to find the ports. Ive had both TB off for cleaning and found a split in the left boot which was sucking air. Easy replac3ment... What I noticed : if you hold the TB upto a bright light and look thru it with the butterfly all the way closed you will find the Left TB throttle plate DOESNT seat tightly against the inner TB bore (id say it allows 3 -4 % gap around the plate) The Right TB when veiwed the same way goes dark. Very tight seal around the plate as it seats correctly at idle. I would assume that the idle screws are designed to deal with this inaccuracy thru the balancing process but shouldnt i attempt to get the plate the seal a little bit better on my left TB? Maybe slightly increase the hole size for the screw to allow for a better seat before tightening it? Am I chasing ghosts here in a desperate attempt to figure out the backfiring thing in the abscence of my much needed vacuum port adapters? 

[Lucky Phil]

12 minutes ago, Beemrguzt said:

So I am a new V11 Sport owner and would like some opinions on something. I of course have that weird left side hiccup at low idle rpms. Ive been trying to get my hands on a set of vacuum ports to screw in to my manifold to do the balancing. Pretty hard to come by. Anyone have a "buy now" source for these ports? So heres my theory, since i have a differential manometer but no ports to attach it to Ive been going over just about everything on the bike while I wait to find the ports. Ive had both TB off for cleaning and found a split in the left boot which was sucking air. Easy replac3ment... What I noticed : if you hold the TB upto a bright light and look thru it with the butterfly all the way closed you will find the Left TB throttle plate DOESNT seat tightly against the inner TB bore (id say it allows 3 -4 % gap around the plate) The Right TB when veiwed the same way goes dark. Very tight seal around the plate as it seats correctly at idle. I would assume that the idle screws are designed to deal with this inaccuracy thru the balancing process but shouldnt i attempt to get the plate the seal a little bit better on my left TB? Maybe slightly increase the hole size for the screw to allow for a better seat before tightening it? Am I chasing ghosts here in a desperate attempt to figure out the backfiring thing in the abscence of my much needed vacuum port adapters? 

If the throttle plate isn't bottoming on the idle stop screw you may be able to loosen the plate screws a little and close the throttle tight to align the plate better. Other than that it's probably wear on the TB bore thats the issue. The screws are tight and staked in but should loosen the 1/2 turn or so and allow some movement. Don't try and remove them without grinding off the staking or you risk damaging the shaft threads.

Check your valve clearances as well if not already done. If nothing else works you could try adjusting the fuel map for the left cylinder a little or even the CO to see if it has an affect.

Phil 

Edited November 26 by Lucky Phil

[docc]

9 minutes ago, Beemrguzt said:

So I am a new V11 Sport owner and would like some opinions on something. I of course have that weird left side hiccup at low idle rpms. Ive been trying to get my hands on a set of vacuum ports to screw in to my manifold to do the balancing. Pretty hard to come by. Anyone have a "buy now" source for these ports? So heres my theory, since i have a differential manometer but no ports to attach it to Ive been going over just about everything on the bike while I wait to find the ports. Ive had both TB off for cleaning and found a split in the left boot which was sucking air. Easy replac3ment... What I noticed : if you hold the TB upto a bright light and look thru it with the butterfly all the way closed you will find the Left TB throttle plate DOESNT seat tightly against the inner TB bore (id say it allows 3 -4 % gap around the plate) The Right TB when veiwed the same way goes dark. Very tight seal around the plate as it seats correctly at idle. I would assume that the idle screws are designed to deal with this inaccuracy thru the balancing process but shouldnt i attempt to get the plate the seal a little bit better on my left TB? Maybe slightly increase the hole size for the screw to allow for a better seat before tightening it? Am I chasing ghosts here in a desperate attempt to figure out the backfiring thing in the abscence of my much needed vacuum port adapters? 

Of course it would be ideal if the throttle body plates closed completely, but it is only critical on the right as that is how the TPS is indexed to the ECU's "map." Once the TPS is set and the throttle bodies are linked and balanced, the left side throttle plate issue simply goes away.

Balancing apparatus ("apparati?" ) typically come with an assortment of vacuum taps. Perhaps these could be had separately from a source like Motion Pro?

Certainly dedicate the process to the "Decent Tune-up" as a baseline, and be certain your relays are upgraded to proper high current items . . .

 

[Lucky Phil]

Thing is docc if the l/h TB gap in the fully closed position is bigger than the position it would be to get a balanced idle then you'll never achieve proper balance. At the bottom of the throttle blade position barely off the stop the movement of the throttle blade is a lot more sensitive than with the throttle open a little so the sensitivity decreases as you open the throttle. Tiny variations on a close throttle make a big difference to vacuum and is why the TB's are fitted with bypass screws. I know most don't use the l/h idle screw and rely on the r/h screw and the linkage to control the idle for the l/h side but if the wear in the lhs fully closed is more than whats required for a decent idle you'll have problems. I'm pretty sure the blades are also matched to the t/b's and they need to be re fitted the right way around as well when re assembling.

Phil

      

[docc]

22 minutes ago, Lucky Phil said:

Thing is docc if the l/h TB gap in the fully closed position is bigger than the position it would be to get a balanced idle then you'll never achieve proper balance. At the bottom of the throttle blade position barely off the stop the movement of the throttle blade is a lot more sensitive than with the throttle open a little so the sensitivity decreases as you open the throttle. Tiny variations on a close throttle make a big difference to vacuum and is why the TB's are fitted with bypass screws. I know most don't use the l/h idle screw and rely on the r/h screw and the linkage to control the idle for the l/h side but if the wear in the lhs fully closed is more than whats required for a decent idle you'll have problems. I'm pretty sure the blades are also matched to the t/b's and they need to be re fitted the right way around as well when re assembling.

Phil

      

Trying to understand . . .

I know we drive on different sides of the road, but I rely on the "l/h" idle screw (on the throttle cable side) to set the idle and keep my "r/h" idle screw defeated.  Sure my entire set-up is worn "slap-out" as they say here in the hills, but works for me.

As far as the left throttle plate not closing completely in the bore, as long as it is less than 3.6º (idle opening), then I expect it to be a non-issue once the system is balanced and brought to idle. I like my idle on the high side (1250+), so even less likely that issue would be problematic as long as the throttle bodies come in to balance "at some rpm" and at idle whether using the Air Bypass Screws and/or the l/h + r/h idle stop screws.

 

[Lucky Phil]

1 hour ago, docc said:

Trying to understand . . .

I know we drive on different sides of the road, but I rely on the "l/h" idle screw (on the throttle cable side) to set the idle and keep my "r/h" idle screw defeated.  Sure my entire set-up is worn "slap-out" as they say here in the hills, but works for me.

As far as the left throttle plate not closing completely in the bore, as long as it is less than 3.6º (idle opening), then I expect it to be a non-issue once the system is balanced and brought to idle. I like my idle on the high side (1250+), so even less likely that issue would be problematic as long as the throttle bodies come in to balance "at some rpm" and at idle whether using the Air Bypass Screws and/or the l/h + r/h idle stop screws.

 

Yes docc you are right we use the l/h idle screw not the right. It's been a while since I did the balance on my bike. Still not sure it's a good thing to have a situation where the blade wont fully close though. Would mean that through the entire throttle range you'd have a slightly larger throttle bore in effect. Probably not an issue at WOT or 50% but maybe at small cruising throttle angles when the ECU is calibrated to the r/h TB flow rate and the L/H is considerably more.

[Lucky Phil]

Not sure why the l/h TB would be worn in the bore if we use the l/h idle screw stop. Might be an assembly issue?

Phil

[GuzziMoto]

My opinion; There is an idle set screw on each throttlebody, but you really should only need to set the one on the throttlebody the throttle cable attaches to. The other one can be screwed in so it is out of the way and does nothing. The other side throttlebody is set by balancing that one to the other one using the adjuster in the linkage. If I remember it right, the throttle cable attaches to the left side throttlebody. And then that side is connected to the right side via the linkage, and the TPS is on the right side throttle body. If you set the left side throttle stop to set the idle, and balance the right side throttlebody to the left, the two throttle bodies will open at the same time regardless of the minor amount of play in the system. If you use the right side idle set screw that can create a difference in the moment of opening between the two sides. Just set the idle based on the throttlebody that the throttle cable directly acts on. Then balance the other one to that one and don't use that sides idle set screw. Think of the system as the throttle cable opens one of the throttlebodies, and the other throttlebody is slaved to the first one.

Probably a good time to mention that often people have their idle set too low. Basing idle speed on the tach can feed into that as often the tach reads high at idle. As Phil said, an idle over a thousand rpm, perhaps in the 1,200 rpm range, is good. But don't base that on what the tach says.

Edited November 26 by GuzziMoto

[audiomick]

3 hours ago, GuzziMoto said:

...But don't base that on what the tach says.

Did somebody just whisper "Guzzidiag"?