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Discussion Starter #1
Hi, I wonder if someone could throw some light on issues I have been having with my ST4s. Back in 2016 I overhauled and serviced the bike including belt change. I changed the stock plugs for iridium ones and after a lot of reading on various forums, also replaced the plug leads for some Blue Magecore ones.



After, I had a problem whereby if the bike is revved, then the instant the revs drop at their lowest point on he rev counter, if its revved again, the bike cuts out. I researched a lot of info on iridium plugs re. gap settings before I replaced these and chose to change the gap from the pre-set to 1mm. I never used the bike much since the 2016 overhaul and have have just serviced it again including replacing belts and cleaning the plugs and still have the same issue. It worked fine before I did the work back in 2016 with the original plugs/wires. I just wish to get the bike right and dont wish it cutting out when I least need it..


Stu
 

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How about changing the plugs back to normal ones and see what happens? Plugs are cheap.
 

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The clearest step is to re-install stock plugs (as per owner's manual) and wires to see if the problem goes away.

Otherwise, what do you mean by "overhaul"? It normally implies disassembly of the engine, replacing bearings, rings, etc. Was it that or a simple service with belts, valve adjustment, oil change and such?

How well and how long did it run afterwards? You're messing with the plugs a lot - do they show specific signs of malfunction like carbon or oil build up?

Some of the signs could be explained if the cam timing is off a notch, that is, the belt(s) were not lined up with the right notch. If it's not off too far, the engine will run fine at either low rpm or high, but not both.
 

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Discussion Starter #5
How about changing the plugs back to normal ones and see what happens? Plugs are cheap.
As it happens, I did this yesterday as I managed to find the original plugs and leads. The problems still present.


HiFlite said:
The clearest step is to re-install stock plugs (as per owner's manual) and wires to see if the problem goes away.

Otherwise, what do you mean by "overhaul"? It normally implies disassembly of the engine, replacing bearings, rings, etc. Was it that or a simple service with belts, valve adjustment, oil change and such?

How well and how long did it run afterwards? You're messing with the plugs a lot - do they show specific signs of malfunction like carbon or oil build up?

Some of the signs could be explained if the cam timing is off a notch, that is, the belt(s) were not lined up with the right notch. If it's not off too far, the engine will run fine at either low rpm or high, but not both.
The bike had been off the road for a very long time. Maybe 8 years or more. In 2016 I overhauled the rear suspension, changed all the filters, fluids and belts. No other engine work was carried out. I went belt and braces and marked the old belts where the timing marks were, then counted the teeth on the new ones even lining the old against the new belts, to make sure they were the same. After the new belts were installed, I rotated the engine numerous times to ensure all three timing marks lined up as they should every time and even to the point whereby my new marks on the belts all lined up with the timing marks on the bike after rotating the engine over a lot.. Can I assume this means they were done correctly? I remember having the problem back in 2016 when I did all the work, but lived with it.

Basically, the bike was never used much since 2016 and stored until now. So I have replaced the belts again, changed the fluids again and oil filter. The plugs do look fouled even after just cleaning and running for short amount of runtime.





I did put the old plugs/wires back in, checked the gaps against the workshop manual and its the same. I adjusted the idle just over 1100 to overcome it and although its more resilient its not resolved the issue totally. I appreciate this is likely to be just masking the issue. Its the short bursts of revs to about which are problematic. Its not something that I do in real life riding. But there appears to be something amiss.

I dont know if due to the very long time the bikes been stored, not used and not been set up, whether it needs setting up. I have not tampered with anything other than the idle.


belter said:
does this problem occur on the road, or just revving it in neutral?

So far, I have only been running it on the drive in neutral.


Many thanks to all of you who have replied - Stu
 

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Spark plugs make a spark. If they are making a spark and the bike is running good when coming on the throttle (throttle response) and at higher RPMs, they are likely fine... The issues people have with Iridium plugs are normally cured with the larger gap and even new (better) wires. You've done that. It's easy to point to the plugs as the cause of your problems because it is something you changed. You could change back to OEM, easy enough. You also said you were in there doing a service. Did you do anything to the TPS adjustment, throttle stop screws, fuel trim, air bleeds??? If not, maybe you need to. If you did, do it again correctly. The problem you have seems more like a set up issue than any particular plug and wire combo.
 

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Discussion Starter #8
Looks like we were typing at the same time.

Grab a fresh coffee and read.
BikeBoy.org - Ducati 4V Desmoquattro Non Linear TPS Baseline Adjustment (plus ST3)

And get some fresh gas in the tank if you haven't already.
Hi, yes I put fresh fuel into the tank as I didnt wish to be caught by elementary stuff ha ha ha

No, I have not touched the TPS or anything to do with the fuel delivery system. Interestingly, I did see that link yesterday whilst trawling the net, as I was starting to think along those lines. I have put the bike back to the original plugs and wires just to eliminate it. I read through the link and think it maybe a little bit beyond my capabilities and I may opt to take it to Duke guru for a pro setup..
 

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The bike had been off the road for a very long time. Maybe 8 years or more. In 2016 I overhauled the rear suspension, changed all the filters, fluids and belts. No other engine work was carried out. I went belt and braces and marked the old belts where the timing marks were, then counted the teeth on the new ones even lining the old against the new belts, to make sure they were the same. After the new belts were installed, I rotated the engine numerous times to ensure all three timing marks lined up as they should every time and even to the point whereby my new marks on the belts all lined up with the timing marks on the bike after rotating the engine over a lot.. Can I assume this means they were done correctly? I remember having the problem back in 2016 when I did all the work, but lived with it.
Did it run well before you did the work? If not, you may have "copied" bad cam timing, if so, you likely created it. While what you did makes some sort of sense, this is not the correct way to set the cams. Briefly, one is supposed to rotate the engine so that the mark on the layshaft (the notched wheel driven by the engine) lines up with a mark on the case. In that position, marks on the cam wheels should line up with their respective marks on the heads. Belts are removed and replaced while keeping the alignment or rotating the camshafts as needed to get it. Belt tension needs to be set in a very specific way too, using pro equipment or the semi-notorious "hex wrench method". Get a maintenance guide from Desmotimes for details. (It should be required reading for every owner regardless of whether one does hands on work or not, IMO).

Basically, the bike was never used much since 2016 and stored until now. So I have replaced the belts again, changed the fluids again and oil filter. The plugs do look fouled even after just cleaning and running for short amount of runtime.
Plug is seriously ugly!

My bet is still on cam timing, but, besides what's already been mentioned, it could also be the notorious-for-failing coolant temperature sensors. At least on the ST2, there are two. One only feeds info to the display, the other to the ECU. If the ECU thinks erroneously that the engine is cold, it sends too much fuel. The engine will initially start and run ok, but run progressively worse as it warms and especially so when accelerating since the mixture is already richened in the normal fuel maps. Plenty of info in the ST forum on troubleshooting and replacement of the sensors.
 

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One easy thing to look at is the ring of goo that can build up in the throttle bores thanks (I think) to Ethanol fuel. Whenever I do a service or feel the idle has dropped a bit, I open open the air box and remove the filter. Have someone hold the throttle wide open for you. You can do it yourself, but having an extra hand here helps a lot with reaching the front bore. With a rag soaked in carb or brake cleaner, wipe clean the bore where the throttle butterfly would sit when the throttle is closed. I often find a build up of waxy goo there that limits air flow at idle. This will create a rich condition at idle, lowering the idle, and can cause temptation to crank in the throttle stop screw. No need if it was set correctly to start with, just clean it. I'd imagine if it was bad enough it may cause your problem when chopping the throttle from high RPMs. Worth a look.
 

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Discussion Starter #12
Did it run well before you did the work? If not, you may have "copied" bad cam timing, if so, you likely created it. While what you did makes some sort of sense, this is not the correct way to set the cams. Briefly, one is supposed to rotate the engine so that the mark on the layshaft (the notched wheel driven by the engine) lines up with a mark on the case. In that position, marks on the cam wheels should line up with their respective marks on the heads. Belts are removed and replaced while keeping the alignment or rotating the camshafts as needed to get it. Belt tension needs to be set in a very specific way too, using pro equipment or the semi-notorious "hex wrench method". Get a maintenance guide from Desmotimes for details. (It should be required reading for every owner regardless of whether one does hands on work or not, IMO).



Plug is seriously ugly!

My bet is still on cam timing, but, besides what's already been mentioned, it could also be the notorious-for-failing coolant temperature sensors. At least on the ST2, there are two. One only feeds info to the display, the other to the ECU. If the ECU thinks erroneously that the engine is cold, it sends too much fuel. The engine will initially start and run ok, but run progressively worse as it warms and especially so when accelerating since the mixture is already richened in the normal fuel maps. Plenty of info in the ST forum on troubleshooting and replacement of the sensors.

As for it running properly, it was so many years ago that it ran prior to me doing the first lot of work in 2016. I never ran it in 2016 due to it having old fuel in her tank and the tank had gone rusty, so I didnt wish add a problem.

I ensured the layshaft mark was lined up with the mark on the case and the cams were also lined up with their respective marks at the same time, before changing the belts the first time. Then with the layshaft and cams all in the same position I changed the belts. After tensioning using the sonic method (mic on my laptop and downloaded french belt tensioning software) with the horizontal cylinder adjusted with all the timing marks aligned and then the vertical one adjusted with the engine turned 270 degrees in advanced. This is how I did it both times.

So if I now rotate the engine and the timing mark on the layshaft aligns with the case and at the same time all 4 cam marks line up with the marks on the case, is this not an indication the belts were changed correctly both times ?
 

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So if I now rotate the engine and the timing mark on the layshaft aligns with the case and at the same time all 4 cam marks line up with the marks on the case, is this not an indication the belts were changed correctly both times ?
Yup!
 

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Discussion Starter #14
Thanks Hiflite,, I will look to get it into a specialist to be thoroughly checked out.. Many thanks for your assistance..
 
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