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Thread: Winter Layup - 1995 Ducati 900 Supersport

  1. #631
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    14th July 2006 - 21:39
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    2015, Ducati Streetfighter
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    Christchurch
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    (2) be good for another 25,000. And you know something else will shit itself before that

  2. #632
    Join Date
    3rd February 2004 - 08:11
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    1982 Suzuki GS1100GK, 2008 KLR650
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    The carbs were rattling before, you just couldn't hear them over the noise the clutch was making. fix the clutch, now its the carbs. Fix the carbs, it will be something else (loose rivets inside the exhaust cans, for example) Ducati Whack-a-Mole.
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  3. #633
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Quote Originally Posted by pete376403 View Post
    The carbs were rattling before, you just couldn't hear them over the noise the clutch was making. fix the clutch, now its the carbs. Fix the carbs, it will be something else (loose rivets inside the exhaust cans, for example) Ducati Whack-a-Mole.
    Well... I was a good sport about this sort of thing before but maybe not this time.

    If I post something, it's because I believe it's useful to someone else out there. That's it. Most of the work I'm covering these days is stuff that's completely off the manual and / or not covered elsewhere on the web, that's why I go into such detail about it.

    The latest with the carburettors, for example... it's four cheapo aluminium rivets that somehow are affecting the entire bike. The job itself is almost trivial. It's just that as far as I've searched, nobody else seems to have posted about the rivets. The closest I got was a post on the ADV forums talking about the rollers having worn. There's quite a few of these FCRs out there. This problem will have happened on other bikes. Other riders could use this info.

    Your latest replies are not helping with that.

    I have little or no time for the game of Get One Up On The Other Guy, Pete, or the people who play it. Now you helped me out before and I appreciate that, but not the cheap shots. Try and be better than that, at least in this thread, alright?

  4. #634
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    a few bits and bobs and a surprise

    Right, some work over the last week.

    I've opted to re-clamp the FCR roller pin rivets. Relatively quick job, using a toolmaker's vise and winding it up via an Allen key - seems to have worked so far. The rivets aren't loose any more. The slides still have free play though... this will reset a rivet, it won't compensate for wear on the roller wheel.

    While I was in I also rebalanced the carbs, using a drill bit shank as a feeler gauge instead of comparing vacuums. The balance adjustment is via a very cute push screw and pull nut, which raise and lower the yoke arm on the throttle shaft. They lock against each other but otherwise don't restrict each other, however it's generally best to loosen the nut first. It is possible to balance the carbs via vacuum, it's just that it's much faster and easier to do it this way.

    The brake and clutch levers were improved. This turned out to be as simple as changing the bolt on the position selector pivot... the original uses a threaded portion of the fastener as a bearing. The marks can be seen inside the brass bushing. It's also carved its way into the aluminium of the lever itself. The shouldered bolt that I wanted (shoulder anywhere it functioned as a bushing, thread after that) turned out to have to be cut down from an M5 x 50 cap screw... I had to use a die and die stock on the original fastener to get a thread of the right length, then shorten the screw to suit. Such a small thing - roughly 10% of clutch travel was restored by doing this, the lever has gradually been getting closer to the handlebar due to the screw thread cutting into the bushing.

    The surprise from the week was found while working on the ST2's clutch. I finally compared a near new clutch basket with a very well worn unit. Guess what... Ducati actually did get the axial clearance right, a brand new unit has very little free play on the gearbox input shaft. The 2.75mm clearance seen earlier was due to wear. Whoops. My mistake.

    The broad, flat, 6-point washer cuts its way into the aluminium clutch hub over time. This is shown clearly in the last photo, the two hubs side by side are from the same manufacturer, it's just that one has a lot of k's on it compared to the other. The washer has sunk its way down into the hub. I've never seen anything like this before.

    I don't know what the wear mechanism is. The washer is a near perfect fit to the worn hub, there's no looseness or free play. It sockets into place perfectly. A mystery, but for now I'll simply take it as proof that I should replace the hub currently in service.

    I did manage to get the bike out for a brief ride which was pretty good.
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  5. #635
    Join Date
    28th January 2015 - 16:17
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    The ongoing mission to sort out why the hell the bike is running badly continues... I've been at it again off and on for the last few months.

    The first suspect was failed crimp connectors in the wiring loom to the coils. This came about after noticing heat damage to one of the connector boots.

    The connector is carrying 12 to 14 V to a load resistance of 5-ish ohms - that's around 2.25 Amps current. It doesn't take much of a resistance on the crimp itself to turn a previously healthy connector into a minature heater element.

    After replacement (some wiring included) and refitting - nope, it wasn't that.

    The next suspect was the fuel pump and the wiring to it, the stuff that goes through epoxy in the connector under the tank. A pretty quick voltage over the pump test showed it was fine - and getting a mechanic's mirror and a penlight into the tank showed that the pump was putting enough fuel through the line that the return was basically a fountain. The pump terminals are accessible without disassembly, if you have long enough test leads or can improvise them.
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  6. #636
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Magnetic circuit around ignition coils

    I got stuck into thinking about the ignition setup last night, after noticing minor damage to the coil HT leads insulation from contacting the battery box. Why were the coils and modules so close together, was this a problem and why? I did a lot of reading and realised something - I haven't paid any attention whatever to the ignition coil's magnetic circuit.

    The bike uses an inductive discharge ignition - transistorised is the term frequently used - which depends on energy stored in the inductance of the coils.

    I found a very good document online from McLaren Electrical Systems which discussed CDI vs Transistorised Ignition Coils. Key points of Transistorised Coil Systems were:

    - the coil stores energy as well as acting as a voltage transformer

    - coil inductance must be relatively high

    - switching rate is limited by time to charge the inductance

    - primary voltage is low and current is high so connecting cables must be thick and short

    - magnetic circuit design is critical and can be affected by location in the engine

    - burn time is long

    - EMI (electromagnetic interference) is severe in high performance systems

    Food for thought. Is it possible that the coils are interfering with one another, not electrically, but magnetically? Is it also possible that the HT leads (which are rubbing on the steel, non-grounded, battery box) are coupling to input wiring via stray capacitance?

    Further checking showed me something else. The coils are mounted in what originally looked like a strange arrangement: there's a threaded spacer which is bolted to the coil bracket. The coil is then screwed to the spacer. There's a fastener at each end of the spacer. Odd. Why not just use a through bolt and a nut?

    It turns out that this aluminium spacer functions as a magnetic insulator post. There's something called permeability, the ability of a substance to carry a magnetic field.

    Air, most plastics, aluminium, water, bone, wood... these all have the same permeability as free space, i.e., not much.

    Magnetic steels, ordinary steels, iron etc has much higher permeability - around 4000 times as much. It's very non linear.

    I've cut the aluminium spacers right down in order to get the coils and HT leads to fit (just) into the home made steel battery box. The spacers originally had 5mm space internally between fasteners. They now have around 0.25 mm (I spent a while being picky and making things only just fit). If there was magnetic impedance there, I've greatly reduced it.

    The other thing is that the steel Ducati OEM coil mounting bracket, which originally fit onto an ABS airbox, is now mounted directly on a thick walled mild steel battery box. The steel is thick and wide enough to be comparable in cross section to the coil inner laminated core.

    I have no idea how to measure or prove this, but it looks like I've mistakenly installed a magnetic short circuit network.

    The coils on the ST2 are set forward, on outside and opposite sides of the frame. They're barely tucked away inside the side fairing panels. It isn't possible to get them further away from the rest of the bike, the control wiring, ignition pickups, ignition control module or each other. They're also mounted on aluminium brackets via rubber grommets and feature what look like completely closed iron cores. It couldn't be more different to the basic design on the 900SS.

    The ST2 has run like a charm in the entire time I've had it, the ignition and fuelling have always been super smooth. Maybe this is the next thing to try - separate the coils and get these mounted in similar physical placements.
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  7. #637
    Join Date
    2nd March 2018 - 15:32
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    1998 Yamaha R1
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    Auckland
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    524
    Yes, the coil mounting can be important. Also whether or not the secondary is grounded, although get that wrong and they tend not to work at all.

    I certainly wouldn't put coils inside a steel box.

    Can you easily go back to the factory mounts?

  8. #638
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    The yellowish bracket is the original factory mount and the alloy spacers mounting the coils can be replaced, so, yes, not really an issue. Refit the original ABS airbox and I'm back to the stock system. There were issues with that setup which was the reason to go to pods, which were the reason to replace the battery box (which was part of the airbox), etc etc.

    The main issue to my mind with a return to stock is that it was compromised design in the first place. It works - but not well...

    - coils right next to each other and 270 degree timing
    - coils mounted on a common bracket made of a high permeability material
    - coils under fuel tank, effectively a three-sided metal box, well it's good for keeping the rain off
    - ignitor units and pickup leads right next to coils and HT leads

    Anyway I'm keen to try a rough copy of the ST2 arrangement. Shouldn't be too hard to trial a setup.
    Last edited by OddDuck; 4th December 2018 at 17:45. Reason: spelling

  9. #639
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    28th January 2015 - 16:17
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    Right, have put the coils onto the flanks of the bike - see photos. The coils are mounted on non-magnetic plates which have basic vibration isolation. I haven't weather sealed the LT connectors yet, wanting to keep this easy to work with for now.

    Testing showed that this is working, there's clean idling and then advance to the maximum position on both cylinders.

    While doing this I finally noticed something about my cheapo fabulous Supercheap Auto timing strobe gun: the inductive pickup has a direction. The arrow on the top points to the spark plug, as properly clipped onto the relevant HT lead. I've carefully coloured it in via Sharpie so that the thing stands out for the picture. Normally it's just moulded plastic which is all the same colour, hence my total failure to notice it. Clip the pickup on backwards and the gun simply doesn't work.

    I've spent years thinking that there's something untraceably weird going on with the ignition for the horizontal cylinder. Gun just won't fire. The ignition has been fine all along, the issue is (and always has been) that the HT lead for the vertical cylinder goes to the right, the HT lead for the horizontal cylinder goes to the left. That's all it took. Whoops.

    Right... putting that aside, I might have something useful for anyone running FCRs on a twin: it's possible to vacuum-synchronise them. All you need is reasonably quick access to the top cover plate of one carburettor. In this setup I have the throttle cables disconnected. Pop them out of their mounting rubbers, take the top plate off, and move the slide position by a marked increment via tweaking the pin screw and nut on the slide yoke. Reassemble, re-test, move again as needed.

    Anyway, the bike's running, still running rough though. Attention to the carburettors looks like the next step.
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  10. #640
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    28th January 2015 - 16:17
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    FCR's - Part 1

    I've attached a chart of Keihin's FCR needle sizing and their geometry. I'd had EMT's supplied with the carburettors and for a long time I've been thinking that they weren't right for the pod filters. The carbs would run OK at about 1/8th throttle to maybe 1/4 and then get progressively more and more lean. After another effort tuning recently, attempting to sort the super rich behaviour at and just off idle, the bike's lean as soon as it's on 1/8th throttle. According to the tuning chart, that's when the needle root diameter becomes the dominant variable.

    I'd taken a punt earlier on a pair of needles with the next steeper taper angle, FMU's by code. I hadn't properly appreciated the importance of the root diameter: they're the next step bigger than the EMTs, and the bike simply wouldn't run past 4000 RPM or over 1/8th throttle. It just bogged out.

    So... a pair of useless carb needles, which happen to have the taper I want. I've got another order in, with a series of F taper needles in various root diameters, but from experience it could be six weeks before delivery. So: the current FMU needles are expendable, it's not the end of the world if I stuff them. Is it possible to reduce the root diameter to a controllable number while keeping this d1 straight?

    Some careful work with a micrometer, 800 grit paper, a drill press on roughly 750 RPM, and a rough tool to try to keep sanding pressure even along the length of interest, and the answer is a very conditional yes.

    It can be done (sort of), it's painstakingly slow and fiddly, and there's a very high chance of bending the needle along the way. Rotating speeds have to be kept low. Initially I tried in a Dremel and it doesn't take much in the way of RPM before the needle starts to bow, if I hadn't been ramping speed up gradually it would have been very easy to bend the needle purely by spinning it.

    Cutting speed (ie diameter reduction) depends greatly on pressure, if the paper is squeezed directly between two fingers then the cut takes off and also tends to dish. This can be useful if sorting specific marked areas along the d1 length though.

    I managed to reduce both needles from 2.785 mm to between 2.755 to 2.760. There's no way they're as straight or precise as stock needles. However I now have a pair of FMR-ish needles and these should give a slightly richer mixture at 1/8th throttle. I haven't had the chance to try them properly yet.
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  11. #641
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    28th January 2015 - 16:17
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    FCR's - Rattling Slides, Part 1

    While playing with the latest round of tuning (sorting the mixture at idle, slow jets etc) I noticed inconsistency in the idle mixture, as shown by the AFR sensor. It'd indicate variation from 12 to nearly 17.

    Rattly slides. OK... maybe they're rattling far enough that the vacuum breaker plate is opening up, letting more air in than is supposed to be there. The rattle back and forth wouldn't be in sync with the engine vibration, hence the variation. I tried revving the engine a bit and listened closely: the rattling doesn't appear to go away with revs. It gets quieter, and certainly gets covered with other noise, but it's still there.

    The way that Keihin designed the FCRs is based around a solution to a problem: simple slide carbs tend to stick at partial or closed throttle, due to high manifold vacuum. Keihin's solution was to use a vacuum breaker plate, which reduces the pressure differential to the point where there's minimal clamping force, while still controlling airflow.

    The vacuum breaker plate is carried in a slide, equipped with rollers. This slide also carries the needle. The rollers are some kind of high-grade engineering plastic, made to survive heat and petrol. Three of the wheels are mounted on roller bearings, the fourth (right upper I think) is pure plastic and very slightly smaller than the other three. The whole thing rolls up or down in a rectangular chute in the carburettor body.

    Basically, the vacuum plate controls airflow. The slide governs position and copes with force from pulsating airflow, keeping the vacuum plate in place as lightly as possible.

    This very light placement is necessary for two reasons:

    1) the lighter the contact force, the longer the vacuum plate / carburettor body interface surfaces will last against wear.
    2) light placement force (and immunity to vacuum force) means a light throttle action. The throttle will close properly when released and won't require a strong twist to open again.

    The photos show the seal between the vacuum plate and the slide - from the edge, it's a tapered, face contact seal. There's a small amount of squish range available which it'll seal over, ie there's a tolerance for the slide moving inward or outwards inside the carburettor body. It's not a broad tolerance and the way this seal works, it'd be best if there was no movement at all.

    The issue with the FCR (these ones at least) is the free play in the slide assembly. I managed to get a 0.203mm feeler gauge to fit between roller wheels and their tracks in the carb body.
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  12. #642
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    28th January 2015 - 16:17
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    FCR's - Rattling Slides, Part 2

    Limited to 6 photos for previous post.

    The first shot is a tighter pic of the slide and sealing face of the breaker plate.

    The second shot is a look down the slideway of the carburettor: I've found a couple of dips in the rail surfaces, apparently due to wear. They look like they match the wheels and there seem to be two sets, one at idle and another at my most frequently used open road throttle setting. One of these dips is center in the photo. It seems very small and was difficult to get a picture of unfortunately. This is on the vacuum plate side, so would actually increase clamping pressure on the plate. The inlet side's slide surfaces still looked OK.

    The last image is the shot of the test for whether the slide clearance lets the vacuum breaker plate open up: lay a ruler or straight edge between the two lower slide wheels, with the feeler gauge in place to simulate the slide having been thrown forward and away from the breaker plate, then see if there's a visible clearance. A torch behind the ruler helps.

    Yep. There is a clearance on this unit, albeit very small. It's opening up due to vibration.

    Maybe the wheels have worn a bit and lost diameter, maybe I've lost material from the rail surfaces. Maybe both. Anyway, if this has been happening, what this means is random, cycle by cycle variations in air fuel mixture, which might explain persistent rough running.

    There's a second, very good reason, to sort the rattle out. It hasn't happened to me (thankfully) but I've read reports of the vacuum plates breaking up and then being sucked into the engine. Being hammered back and forth isn't good for anything and these are simply cast aluminium.
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  13. #643
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    28th January 2015 - 16:17
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    FCR's - Rattling Slides, Part 3

    After measuring slack clearance at 0.203mm, I had a try at shimming and found that a clearance is needed for smooth operation. My shims ended up at 0.127mm, which seems to work OK.

    The shim material is brass, not stainless. Brass obviously works, that's what jets etc are all machined from, and I was concerned about the galvanic reaction between stainless steel and aluminium. Fabrication didn't require much gear: drilling between washers, tinsnips, 800-grit paper (for the edges), folding in a bench vise, etc. I used a Dremel to carve the oval slots and should have done the round edges for the throttle throat in this way instead of tinsnipping them. There was a lot of back and forth fine-tuning to make sure that the shims didn't bind up the slides.

    I also wanted the shims positively retained, hence the fold and attachment through the carburettor top cover. If these move, bend, bind or jam, they'll jam the throttles. The far end of the shim plate locates into a narrow gap between two bits of the throttle body so that's supported. The brass is very soft and appears to have picked up wheel marks already, so I'm not sure how long (reasonably) I can expect in terms of service life. They're easy enough to pull and inspect.

    Anyway, results: highly effective at stopping slide clatter and rattle, also effective at restoring consistency to idling mixture. This shimming has affected tuning. The vacuum plate leakage effectively leaned out the mixture. With the rattle reduced, the idle and just off idle tuning has become richer.

    While doing this work I noticed a few fine shreds of rubber caught in the retaining spring of one of the slow air screws. It looks like the ribs on the pod filter necks were being cut by the carburettor trumpets on refitting. I've taken some paper to the trumpet edges and smoothed off the radius.

    The photo of the red coiled air line hose might be useful for someone on a budget, or with limited room: it's a one-shot air duster. Very useful for cleaning out carburettor jets. The bicycle pump (which I owned already) will go up to 120 psi. The hose, gun, nozzle etc was purchased from Repco on special for $20 and all it took to connect to the bike pump was an old inner tube valve and a hose clip.
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  14. #644
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    28th January 2015 - 16:17
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    Some further work - I'm still trying to smooth the bike engine out a bit.

    I've put a baffle between the pod filters. The reasoning for this is that, given the bike's asymmetrical induction timing, one intake will steal from the other if given half a chance. I'm sure that this is the reason that the ST2 features an airbox with a center divider.

    The baffle was worked up via cardboard and a bit of fitting and filing. The black patch stuck to it is a bit of stick-on Velcro, used as an anti-rattle measure. Clearance to the internal roof of the tank cavity is around 4mm, give or take. Working this up took most of a day.

    The second thing was the installation of an O-ring seal on the emulsion tubes. This followed detail measurements taken on the premise that it just might be possible for me to turn up my own emulsion tubes. I decided against, in the end. Too much work. However it did highlight something: the tubes carry petrol on the inside, with flow governed by the needle. On the outside, where they're not supposed to flow, they're sealed only by a close fit between a 5.5mm shoulder and a reamed hole in the carburettor body. It's a clearance fit, metal to metal. There isn't a compressible sealing element. It's totally dependent on tight manufacturing tolerances and the clearance not having opened up via mileage, thermal expansion and contraction and subsequent wear, or the engine shaking like hell and thus rattling the tubes (as might happen during a main bearing failure, for example).

    Philisophically speaking, that means it leaks. No question about it, the metal isn't tight. The question is then, how much?

    The detail measurements, and running some numbers, told me that it's significant in terms of carburettor tuning. Without actually taking measurements or documenting flow around the outside, on the horizontal cylinder, the clearance amounts to roughly 9% of the flow area inside the tube, with a perfect bore and a perfect needle. On the vertical cylinder, it was 20%. That's enough of a mismatch to cause issues.

    The small bore transfer gauges pictured were used to help with making sure that the O-rings would make it into place without getting carved up by either the emulsion tube thread or an internal shoulder. The gauges aren't all that precise, unfortunately. I had to make sizing calls via guesswork: if the 5.5mm hole has been reamed, what are the standard tolerance classes of reamers used, etc. The hand drill and Dremel burr shown were used to open out the thread, clear the sharp-edged feed passage, and put a taper shoulder into the carburettor body bore, with final finishing of the taper surface done by very lightly twirling the burr by hand. It was pure chance that the OD of the burr was 6.35mm and that the taper was about right; the O-ring in its groove was between 6.30 and 6.35 mm OD. And so on. Tight clearances, fiddly and careful work. I can see why Keihin didn't do this.

    While I had the carburettors apart, I took a close look at the emulsion tubes. These are a wear item, since the needle runs in them. They're scored. There are vertical lines of wear running in them. That isn't really surprising, with over 20K miles on them, and I've ordered replacements. Cutting O-ring grooves into worn-out emulsion tubes therefore sounds like a waste of time, but I wanted to test my theory: that leakage around the outside of the tubes was causing some of the engine vibration. The only variable changed was that O-rings were installed.

    End result: both the baffles and the seals helped. I tested these one after the other so can be sure of that statement. They have helped, they're worthwhile. They haven't brought the bike back to 100% the way it should be.

    The annoying bit is that I'd gone for a ride, pre O-rings and baffle, and the bike had been rough as guts until I'd parked for lunch. After lunch, for ten minutes or so, it had been as smooth as it had been earlier. I don't know for sure why. My best guess so far is that enough petrol had turned to varnish on the emulsion tubes that it had covered the scoring and the leakage up.
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  15. #645
    Join Date
    28th January 2015 - 16:17
    Bike
    2000 Ducati ST2
    Location
    Lower Hutt
    Posts
    1,091

    Auxiliary lights

    I've put some aftermarket LEDs onto the bike - both a pair of positioning lights and a pair of auxiliary headlights. The positioning lights have tucked onto a bracket underneath the front fairing. The auxiliaries are mounted on outrigger posts attached to the bike via frame clamps.

    The reason for doing this is pretty simple: be seen, avoid SMIDSY. As a bonus the auxiliary headlights complement the low beam headlight very nicely despite the difference in colour.

    The mounting pattern was chosen for a couple of reasons - I wanted to make the bike as visually wide as possible, also with a broad frontal area vertically. The reason for this is both to get seen and also to give drivers a wide target to estimate oncoming speed and distance properly with. It's difficult to do this with a single point source such as a single motorcycle headlight.

    Kevin Williams - of Science of Being Seen fame - covered this point in his talk at Shiny Side Up. The research clearly indicated that cage drivers had a tendency to see bikes as further away than they were, and also as moving more slowly than they were, simply due to how small and narrow the bike is compared to a car.

    The trick is to make sure that it's still recognisable as a motorcycle. Hopefully the yellow headlight will help with that.

    Part of my installation has the auxiliaries back a bit on the frame so that they're side-lighting the fairing flank, front guard and front wheel. That's so that the bike's obviously a bike, when seen at a side angle at intersections, rather than some random pattern of lights floating around in the dark.
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