Rough running low down and high idle when warm - Page 3

FrankenDesmo · 21-03-2020, 08:11 PM

Quote:

Originally Posted by Dukedesmo

BTW, I don't know where Haynes get their clearances from? - at least for the 4v...

Chris Kelly recommends using a Haynes manual on his valve adjustment page, though he doesn't specifically say to use it for the numbers (but then again he doesn't specifically say not to, either...).

FrankenDesmo · 22-03-2020, 12:10 PM

Had to reconnect the heater as it started pumping out oil while cranking the motor. Looks like the tap doesn't do a hell of a lot at the moment as all I could manage was shutting off the line directly attached to the tap, however the line I assumed was the return was also pumping out oil so I have no idea what's going on there (possible connected to the wrong side of the oil cooler? it's bolted to the same side as the 'inlet' heater pipe). I've got the battery/airbox sitting on top of the bike rather than seated/bolted in, so I should still be able to get at the carbs for sync/adjustments.

Just waiting for the battery to charge as I had drained it a bit cycling the engine without the plugs in to prime the carbs.

BTW while cycling the engine, when I'd let go of the starter there is a ratchet-like noise as the starter spins down and stops - is this normal or is it something like the sprag wearing out?

FrankenDesmo · 22-03-2020, 07:31 PM

And it's alive!

Ended up jumping it off the car since I was too impatient to wait for the battery to get enough charge. After I'd dialed down the idle and let it warm up, I put the carbtune on to find that they were both more or less in sync, but I did fine tune them a wee bit - managed to get them within 1cmHg. In the end, having the airbox off the carbs (but still sitting on top), I could use the mounting holes to get a sight to the sync screw and get a small screwdriver in there (pain in the arse but once I had it lined up it was easier to get it back there between throttle blips).

Idles beautifully at around 1100-1200rpm, pulls away nicely up to past 9k rpm.

When part-throttle cruising at around 4k, it does pop a wee bit, and if I go from part to full throttle (chopping down a gear as well, usually), there is a decent hesitation for a second or two before it pulls away. So something to smooth out (unless it turns out to be due to the valve clearances, in which case it'll wait till winter...).

All in all the bike is running pretty damn nicely and is perfectly rideable as-is. I'm going to take it for a longer ride tomorrow for more of a shakedown.

Edit: This is my 69th post. Nice.

utopia · 20-03-2020, 07:04 PM

I've done my own valve clearance checks three times now.
I also have enough engineering experience to have a decent amount of "feel" with measuring systems.
Just thought I'd pass on what I've learned from work on my own M750, namely ....

The results you get are significantly dependent on the method used.
I favour the method used by Chris Kelly to check the closer clearances but I also measure them directly and compare the results.
Also, no matter what method I'm using, I usually go through the whole lot two or three times, keeping notes as I go.
I always get discrepancies and I'm not satisfied until I have reasonable parity between both the different measurement methods and the repeated attempts at the same method.
This whole process usually takes me two or three days and this is partly because I like to leave a decent gap between my various attempts to reduce the chances of robotic repeats.
I have found in the past that after a few attempts I become much more confident in the validity of my individual measurements and my overall result.
In the past I have been able to detect differences which arise simply from, for example, the method that I use to load the closing rocker.
If you think about it, this isn't surprising as you are measuring the effect of an assembly of parts, each of which has a working clearance.
I also bear in mind that oil on the mating surfaces can affect the results.

I tend to be happy to adjust any clearances which are a little tight and need opening up a bit but I'm more wary of adjusting any that are loose and need closing up ... particularly the closer clearances.
I also disregard any recommendations to aim for zero clearances because I'd rather have a little noise than risk a damaging interference.
Valve clearances which are a small amount out of tolerance, as long as there is no interference, should not cause what you could call a running "fault" with the engine ... they would only fractionally reduce the running efficiency.
Finally, I keep detailed notes of everything as I go along. I also edit these notes into a suitable record for future use.

Personally, I'm not a fan of rubbing shims down to reduce their size. I tend to prefer buying a new shim (or accepting a small amount of difference from perfection).
Its too easy, in my opinion, to change a dead flat surface into a curved or tapered one in the process.
Also bear in mind that the shims are hardened (probably case hardened if they're original Ducati shims but there are aftermarket shims which are hardened right through .. or so I'm told).
But I know there are plenty who do rub shims down in size and seem to get away with it. ... you pays yer money ....

A mirror will provide a reasonable flat surface to work from if you do decide to rub shims down.
It can also make a useful substitution for an engineering surface plate for use in making measurements.

Sorry that's all a bit lengthy, both in words and in the work suggested, but in these days of social isolation you might as well spend a bit longer in the shed, eh ?

Flip · 20-03-2020, 07:53 PM

For another view on valve adjustment and how service intervals and the subsequent running costs of Ducati’s have changed over the years as a result, have a ponder over Neil Spalding’s thoughts.

http://www.sigmaperformance.com/service-interval.html

Now onto the reason I asked about the battery- it is just possible that yours is starting to ‘soft-short’. It’s really hard to detect and it usually won’t register as weak on an Optimate type charger and even more tricky it will often pass a ‘drop test’ too. Only after the bike has been running a few minutes (especially if the charging system is putting in 14v+ which is too high for a sealed battery float charge) it can then show up as a mis-fire, admittedly this would be more likely in a fuel injected motor running a fuel pump and associated ECU but I suppose it is possible it’s somehow sapping power to the coils or igniter boxes?

There’s a lot to read but worth it here:

https://batteryuniversity.com/learn/...internal_short

FrankenDesmo · 20-03-2020, 09:43 PM

I appreciate the the write-up utopia, always good to hear from those that have been there and done that a few times. This was my first time doing a valve clearance check on any vehicle, and I'm fairly sure it's the first time I've ever use feeler gauges in anger. I know that the principle is for there to be a small amount of 'drag' and for the feeler to go in without being forced (or even encouraged), but you know what they say about theory and practice. I'll go through the checking process again tomorrow. Also I can't believe I didn't think of a mirror! I ended up getting what would seem to be a very flat tile from B&Q but a mirror has a much better chance of being true.

I am, however, very tempted to leave them well alone for now - if the impact is on efficiency and less than perfect low RPM running, then I'll take the hit for now while I sort out the more acute low-RPM running issue I've been facing (which I don't think is likely to be caused by valve clearances given it wasn't anywhere near that bad before being parked up over winter). I think at this point I run more risk of getting it wrong, which puts the bike out of action for longer. Whereas over the winter I can take my time with it (and possibly get a shim kit ready from emc ahead of time). Also - I really, really want to ride the bloody thing! I've owned it for 6 months and have barely ridden it - I'll happily do the things that require attention right now, but I am willing to put off those tasks that aren't a pressing issue at the moment.

Going off of the link that flip has shared, it seems that I should be aiming for the assembly tolerances? I do want this bike to last 'forever', however that would mean a full re-shim if my measurements are correct. I think I'd like to take the heads off for that, and do it in the off-season.

Am I being too impatient? Is it silly to leave the valves as-is (for now) if my measurements are correct?

FrankenDesmo · 20-03-2020, 09:48 PM

flip - with the battery, I'll see how it goes once I've got the carbs back on. If I've still got the exact same problem, then that's probably the only 'cheap' bit remaining to replace before I start looking at more serious bits.

manwithredbike · 20-03-2020, 11:03 PM

Would agree with Utopia about rubbing down shims manually, though i think when you consider the effort in re-ordering/waiting time/price etc, it's almost inevitable that you'll try it. I done mine a few years ago after changing the cams and brought my closing shims down a few thou as they were a bit tight. Eventually got them turning sweet, as close to zero as you could get but my first attempt left me with two uneven shims even though i though i was rubbing it flat. Second go, i'm sure was as close to as flat as could be done manually but prob as much carefully slow/luck as tecnique. I had my heads on the bench as well as having a few spare shims to play around with which makes it much easier.

Darren69 · 21-03-2020, 04:41 AM

Yea, I'd get the carbs sorted and bike running sweet then worry about valves. It is unlikely that is the main problem imho from what you've described is most likely fuelling set up or less likely an electrical ignition issue.

jerry · 21-03-2020, 09:24 AM

Problem with shims is that the ones ducati sell u are often a few thou out of spec , so grinding them becomes a chore , also when reassembling the adjustment can change when u refit the collets a different way round from when
they came off ,, im very fussy about this so it takes more time,,

FrankenDesmo · 23-03-2020, 08:10 PM

If you mean those wee pods on either side of the front of the frame, they're still there (for now).

I have had one or two backfires on deceleration, would I think suggests a bit of a lean condition. My suspicion is that this is something to be fine tuned via the pilot screws, and possibly the needle clip, but I'll do some more reading. Unfortunately now that we are in lock down, test runs will be limited to shopping for essentials (though I'm sure I can include the M77 in my route to/from the shops).

After my riding today I think the area where this is occurring is more 4-4.5k rpm, and it is definitely ony under partial throttle (I think up to about 1/4-1/3). From memory of reading lots of posts, this is the typical trouble area for these motors/carbs. Skim reading the sigma performance link you've provided earlier also suggests that the valve clearances could be playing a part.

It's a problem that seems to 'build up' while cruising, too - if I'm constantly up and down the rev range then it barely even coughs, after a wee bit of cruising I'll get a slight hesitation, but after a few minutes of cruising it'll bog down/hesitate quite badly for a couple of seconds before pulling away.

Luddite · 23-03-2020, 08:31 PM

Quote:

Originally Posted by FrankenDesmo

It's a problem that seems to 'build up' while cruising, too - if I'm constantly up and down the rev range then it barely even coughs, after a wee bit of cruising I'll get a slight hesitation, but after a few minutes of cruising it'll bog down/hesitate quite badly for a couple of seconds before pulling away.

Could it possibly be carb icing? Utopia has plenty of experience of this phenomenon so perhaps he can offer an opinion?

utopia · 23-03-2020, 11:44 PM

Well, just as I was reading the last couple of posts I was beginning to think .. hang on, I wonder if its still cold/damp enough around Glasgow to cause carb icing.
My 750 seems particularly prone to this and I can tell you that just two weeks ago, en route to a norfolk meet-up, I experienced the symptoms on the early morning outward run, though by the afternoon return they had disappeared.
In my experience, the symptoms usually arise when I slow down following a period of steady throttle, for example when slowing for a roundabout at the end of a dual carriageway.
Tickover is at first erratic, sometimes non-existent and I need to blip the throttle to stop the engine dying altogether but after being stationary (or very slow) for just a brief period (maybe 20 seconds) the tickover returns to normal, presumably as the engine heat soaks back into the carbs.
If there has been insufficient time for this heat soaking to fully take place, then pulling away is also erratic and requires a handful of throttle to avoid stalling.
That's about the best I can describe my symptoms.
It may not be the cause of your residual issues but one fairly simple test would be to dose the fuel with Silkolene proFST, which will eliminate carb icing if used in sufficient quantity.
Folk also say that using premium fuel also helps, but I always do that anyway.
Oh and it seems to be cold and damp conditions which are the most likely to cause carb icing .. and somewhat counter-intuitively with the accent on the damp rather than the cold.
You could try a run on a warm, dry afternoon.

Good call by Flip on the carb pods, by the way.
I was hoping he'd nailed it there.
But anyway, you seem to have cured the majority of the problem.

Here's a bit of carb pondering that I was going to post earlier but held back in the hope that Flip's suggestion lead to a solution....

I'm no carb expert by any means but if there is a hesitation at mid throttle but it pulls strongly on full throttle, my best guess would be that the needle stage needs a tweek.
But please don't take this as sound advice as I don't have the experience to back it up .. its just food for thought based mostly on received knowledge and limited work on my single cylinder dommie which has recently been revamped with a pod filter and free-flowing exhaust.
I only mention it in case you might find it convenient at this point in time (when you are familiar with the carbs and associated bits and pieces) to try a small adjustment of the needle clip position.

Darren69 · 24-03-2020, 03:15 AM

As per Utopia and Flip if its not carb icing or the pods then you could try dropping the needle clip to raise the needle. I'm no carb expert myself but that's what I would try.

350TSS · 24-03-2020, 04:36 AM

The fact that it occurs at consistent revs/throttle position seems to suggest carburettors and at 4000 to 4500 rpm I think he would be on the transition between the needle and main jet. If it is popping a bit then as well that suggests a weak mixture so raising the needles would be exactly what I would do as well.

20-03-2020, 07:04 PM	#4
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	I've done my own valve clearance checks three times now. I also have enough engineering experience to have a decent amount of "feel" with measuring systems. Just thought I'd pass on what I've learned from work on my own M750, namely .... The results you get are significantly dependent on the method used. I favour the method used by Chris Kelly to check the closer clearances but I also measure them directly and compare the results. Also, no matter what method I'm using, I usually go through the whole lot two or three times, keeping notes as I go. I always get discrepancies and I'm not satisfied until I have reasonable parity between both the different measurement methods and the repeated attempts at the same method. This whole process usually takes me two or three days and this is partly because I like to leave a decent gap between my various attempts to reduce the chances of robotic repeats. I have found in the past that after a few attempts I become much more confident in the validity of my individual measurements and my overall result. In the past I have been able to detect differences which arise simply from, for example, the method that I use to load the closing rocker. If you think about it, this isn't surprising as you are measuring the effect of an assembly of parts, each of which has a working clearance. I also bear in mind that oil on the mating surfaces can affect the results. I tend to be happy to adjust any clearances which are a little tight and need opening up a bit but I'm more wary of adjusting any that are loose and need closing up ... particularly the closer clearances. I also disregard any recommendations to aim for zero clearances because I'd rather have a little noise than risk a damaging interference. Valve clearances which are a small amount out of tolerance, as long as there is no interference, should not cause what you could call a running "fault" with the engine ... they would only fractionally reduce the running efficiency. Finally, I keep detailed notes of everything as I go along. I also edit these notes into a suitable record for future use. Personally, I'm not a fan of rubbing shims down to reduce their size. I tend to prefer buying a new shim (or accepting a small amount of difference from perfection). Its too easy, in my opinion, to change a dead flat surface into a curved or tapered one in the process. Also bear in mind that the shims are hardened (probably case hardened if they're original Ducati shims but there are aftermarket shims which are hardened right through .. or so I'm told). But I know there are plenty who do rub shims down in size and seem to get away with it. ... you pays yer money .... A mirror will provide a reasonable flat surface to work from if you do decide to rub shims down. It can also make a useful substitution for an engineering surface plate for use in making measurements. Sorry that's all a bit lengthy, both in words and in the work suggested, but in these days of social isolation you might as well spend a bit longer in the shed, eh ? Last edited by utopia; 21-03-2020 at 12:59 AM..

20-03-2020, 07:53 PM	#5
Flip Registered User Join Date: Mar 2010 Location: Beachtown Bike: M900 Posts: 2,188	For another view on valve adjustment and how service intervals and the subsequent running costs of Ducati’s have changed over the years as a result, have a ponder over Neil Spalding’s thoughts. http://www.sigmaperformance.com/service-interval.html Now onto the reason I asked about the battery- it is just possible that yours is starting to ‘soft-short’. It’s really hard to detect and it usually won’t register as weak on an Optimate type charger and even more tricky it will often pass a ‘drop test’ too. Only after the bike has been running a few minutes (especially if the charging system is putting in 14v+ which is too high for a sealed battery float charge) it can then show up as a mis-fire, admittedly this would be more likely in a fuel injected motor running a fuel pump and associated ECU but I suppose it is possible it’s somehow sapping power to the coils or igniter boxes? There’s a lot to read but worth it here: https://batteryuniversity.com/learn/...internal_short __________________ You're perfect, yes, it's true- But without me you're only you!

20-03-2020, 11:03 PM	#8
manwithredbike aka Phil Join Date: Nov 2005 Location: derry Bike: M900 Posts: 376	Would agree with Utopia about rubbing down shims manually, though i think when you consider the effort in re-ordering/waiting time/price etc, it's almost inevitable that you'll try it. I done mine a few years ago after changing the cams and brought my closing shims down a few thou as they were a bit tight. Eventually got them turning sweet, as close to zero as you could get but my first attempt left me with two uneven shims even though i though i was rubbing it flat. Second go, i'm sure was as close to as flat as could be done manually but prob as much carefully slow/luck as tecnique. I had my heads on the bench as well as having a few spare shims to play around with which makes it much easier. __________________ .. ~

21-03-2020, 04:41 AM	#9
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,026	Yea, I'd get the carbs sorted and bike running sweet then worry about valves. It is unlikely that is the main problem imho from what you've described is most likely fuelling set up or less likely an electrical ignition issue. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

21-03-2020, 09:24 AM	#10
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,826	Problem with shims is that the ones ducati sell u are often a few thou out of spec , so grinding them becomes a chore , also when reassembling the adjustment can change when u refit the collets a different way round from when they came off ,, im very fussy about this so it takes more time,, __________________ MONSTERMAN

22-03-2020, 12:10 PM	#2
FrankenDesmo Member Join Date: Sep 2019 Location: Glasgow Bike: M900 Posts: 108	Had to reconnect the heater as it started pumping out oil while cranking the motor. Looks like the tap doesn't do a hell of a lot at the moment as all I could manage was shutting off the line directly attached to the tap, however the line I assumed was the return was also pumping out oil so I have no idea what's going on there (possible connected to the wrong side of the oil cooler? it's bolted to the same side as the 'inlet' heater pipe). I've got the battery/airbox sitting on top of the bike rather than seated/bolted in, so I should still be able to get at the carbs for sync/adjustments. Just waiting for the battery to charge as I had drained it a bit cycling the engine without the plugs in to prime the carbs. BTW while cycling the engine, when I'd let go of the starter there is a ratchet-like noise as the starter spins down and stops - is this normal or is it something like the sprag wearing out?

22-03-2020, 07:31 PM	#3
FrankenDesmo Member Join Date: Sep 2019 Location: Glasgow Bike: M900 Posts: 108	And it's alive! Ended up jumping it off the car since I was too impatient to wait for the battery to get enough charge. After I'd dialed down the idle and let it warm up, I put the carbtune on to find that they were both more or less in sync, but I did fine tune them a wee bit - managed to get them within 1cmHg. In the end, having the airbox off the carbs (but still sitting on top), I could use the mounting holes to get a sight to the sync screw and get a small screwdriver in there (pain in the arse but once I had it lined up it was easier to get it back there between throttle blips). Idles beautifully at around 1100-1200rpm, pulls away nicely up to past 9k rpm. When part-throttle cruising at around 4k, it does pop a wee bit, and if I go from part to full throttle (chopping down a gear as well, usually), there is a decent hesitation for a second or two before it pulls away. So something to smooth out (unless it turns out to be due to the valve clearances, in which case it'll wait till winter...). All in all the bike is running pretty damn nicely and is perfectly rideable as-is. I'm going to take it for a longer ride tomorrow for more of a shakedown. Edit: This is my 69th post. Nice.

20-03-2020, 09:43 PM	#6
FrankenDesmo Member Join Date: Sep 2019 Location: Glasgow Bike: M900 Posts: 108	I appreciate the the write-up utopia, always good to hear from those that have been there and done that a few times. This was my first time doing a valve clearance check on any vehicle, and I'm fairly sure it's the first time I've ever use feeler gauges in anger. I know that the principle is for there to be a small amount of 'drag' and for the feeler to go in without being forced (or even encouraged), but you know what they say about theory and practice. I'll go through the checking process again tomorrow. Also I can't believe I didn't think of a mirror! I ended up getting what would seem to be a very flat tile from B&Q but a mirror has a much better chance of being true. I am, however, very tempted to leave them well alone for now - if the impact is on efficiency and less than perfect low RPM running, then I'll take the hit for now while I sort out the more acute low-RPM running issue I've been facing (which I don't think is likely to be caused by valve clearances given it wasn't anywhere near that bad before being parked up over winter). I think at this point I run more risk of getting it wrong, which puts the bike out of action for longer. Whereas over the winter I can take my time with it (and possibly get a shim kit ready from emc ahead of time). Also - I really, really want to ride the bloody thing! I've owned it for 6 months and have barely ridden it - I'll happily do the things that require attention right now, but I am willing to put off those tasks that aren't a pressing issue at the moment. Going off of the link that flip has shared, it seems that I should be aiming for the assembly tolerances? I do want this bike to last 'forever', however that would mean a full re-shim if my measurements are correct. I think I'd like to take the heads off for that, and do it in the off-season. Am I being too impatient? Is it silly to leave the valves as-is (for now) if my measurements are correct?

20-03-2020, 09:48 PM	#7
FrankenDesmo Member Join Date: Sep 2019 Location: Glasgow Bike: M900 Posts: 108	flip - with the battery, I'll see how it goes once I've got the carbs back on. If I've still got the exact same problem, then that's probably the only 'cheap' bit remaining to replace before I start looking at more serious bits.

23-03-2020, 08:10 PM	#11
FrankenDesmo Member Join Date: Sep 2019 Location: Glasgow Bike: M900 Posts: 108	If you mean those wee pods on either side of the front of the frame, they're still there (for now). I have had one or two backfires on deceleration, would I think suggests a bit of a lean condition. My suspicion is that this is something to be fine tuned via the pilot screws, and possibly the needle clip, but I'll do some more reading. Unfortunately now that we are in lock down, test runs will be limited to shopping for essentials (though I'm sure I can include the M77 in my route to/from the shops). After my riding today I think the area where this is occurring is more 4-4.5k rpm, and it is definitely ony under partial throttle (I think up to about 1/4-1/3). From memory of reading lots of posts, this is the typical trouble area for these motors/carbs. Skim reading the sigma performance link you've provided earlier also suggests that the valve clearances could be playing a part. It's a problem that seems to 'build up' while cruising, too - if I'm constantly up and down the rev range then it barely even coughs, after a wee bit of cruising I'll get a slight hesitation, but after a few minutes of cruising it'll bog down/hesitate quite badly for a couple of seconds before pulling away.

23-03-2020, 11:44 PM	#13
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	Well, just as I was reading the last couple of posts I was beginning to think .. hang on, I wonder if its still cold/damp enough around Glasgow to cause carb icing. My 750 seems particularly prone to this and I can tell you that just two weeks ago, en route to a norfolk meet-up, I experienced the symptoms on the early morning outward run, though by the afternoon return they had disappeared. In my experience, the symptoms usually arise when I slow down following a period of steady throttle, for example when slowing for a roundabout at the end of a dual carriageway. Tickover is at first erratic, sometimes non-existent and I need to blip the throttle to stop the engine dying altogether but after being stationary (or very slow) for just a brief period (maybe 20 seconds) the tickover returns to normal, presumably as the engine heat soaks back into the carbs. If there has been insufficient time for this heat soaking to fully take place, then pulling away is also erratic and requires a handful of throttle to avoid stalling. That's about the best I can describe my symptoms. It may not be the cause of your residual issues but one fairly simple test would be to dose the fuel with Silkolene proFST, which will eliminate carb icing if used in sufficient quantity. Folk also say that using premium fuel also helps, but I always do that anyway. Oh and it seems to be cold and damp conditions which are the most likely to cause carb icing .. and somewhat counter-intuitively with the accent on the damp rather than the cold. You could try a run on a warm, dry afternoon. Good call by Flip on the carb pods, by the way. I was hoping he'd nailed it there. But anyway, you seem to have cured the majority of the problem. Here's a bit of carb pondering that I was going to post earlier but held back in the hope that Flip's suggestion lead to a solution.... I'm no carb expert by any means but if there is a hesitation at mid throttle but it pulls strongly on full throttle, my best guess would be that the needle stage needs a tweek. But please don't take this as sound advice as I don't have the experience to back it up .. its just food for thought based mostly on received knowledge and limited work on my single cylinder dommie which has recently been revamped with a pod filter and free-flowing exhaust. I only mention it in case you might find it convenient at this point in time (when you are familiar with the carbs and associated bits and pieces) to try a small adjustment of the needle clip position.

24-03-2020, 03:15 AM	#14
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,026	As per Utopia and Flip if its not carb icing or the pods then you could try dropping the needle clip to raise the needle. I'm no carb expert myself but that's what I would try. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

24-03-2020, 04:36 AM	#15
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	The fact that it occurs at consistent revs/throttle position seems to suggest carburettors and at 4000 to 4500 rpm I think he would be on the transition between the needle and main jet. If it is popping a bit then as well that suggests a weak mixture so raising the needles would be exactly what I would do as well.