Ivan's Jet Kit Installation

Ivan's Jet Kit is designed to enable the carburetors to produce the maximum performance that can be obtained. Factory compromises for emissions and fuel economy are replaced with a goal for optimum performance at all rpm and throttle openings.

The bike has several carburetion problems in it's stock form. The kit takes the approach of fixing all of these problems at their source. There is also no need for any additional 'tuning' after installation. The thorough R&D on the kit makes it truly 'plug and play'. Just install it and go.

  1. Vibration at light steady throttle, most noticeable in the 3800 to 5000 rpm range.

    This is due to the excessively large spacing of the three pilot bypass holes. The throttle plate has to uncover the next hole before more fuel can flow from this circuit. Fitting larger pilot jets will make no difference to steady state operation at light throttle due to the fact that the next hole is not yet uncovered. Raising the needle does not help because the throttle plates have not been open far enough to expose the needle circuit during light throttle cruise. The result is some surging and buzzing. The solution is to:

    • Enlarge the pilot bypass holes. Enlarging these holes in the throat of the carb makes available just the proper amount of additional fuel at exactly the correct throttle opening.
    • Adjust the mixture screws for a richer mix.
    • Synchronize the carburetors.
    • Dynamically adjust the throttle position sensor. This also contributes to the smoothness and takes care of all the ignition timing issues under 4000 rpm.

  2. Flooding when parked overnight causing the throttle to be partially opened when starting cold with the choke.

    This flooding condition is due to excessive fuel in the carburetor's float chambers which overspills slowly when the bike is parked. The cylinders become 'wet' and slighly flooded, causing the rider to be forced to open the throttle slightly on a cold start with the choke. With the jet kit installation the floats are readjusted to alter the fuel level vastly improving the condition.

  3. Overly rich fuel fuel mixture at full throttle above 8000 rpm.

    Full throttle operation above 8000 rpm is overly rich. In order to correct this problem, smaller main jets are supplied optimized for use with the needles that come with the kit. The original main jets that come with the bike are of a different size on cylinders 1&4 as compared to 2&3. Repeated dyno testing and exhaust gas analysis has shown a higher and wider power peak as well as a more consistent fuel mixture throughout the rpm range at full throttle with these new main jets. All of these tests were comfirmed by road testing against another bike under controlled conditions.

  4. Excessively lean fuel mixture at part throttle at any rpm.

    The area of part throttle lean condition can only be fixed with a different needle taper. The single, very shallow, taper of the stock needles simply cannot cope with the fuel requirements to keep a consistent fuel mixture, making more heat, vibration, and lazy acceleration. Ivan's custom needles have five separate angles in their design to give the most consistent fuel delivery possible. The result is a seamless power delivery, excellent mileage, and smooth driveability in normal everyday use with no sacrifice in top end power or midrange roll-on. The needles that were chosen are the result of exhaustive testing in all kinds of weather on the road and on the dyno in conjunction with exhaust gas analysis. Over 70 different prototype needles were tested before settling on the ones that come with Ivan's kit. Over 900 dyno runs were logged as well during development on carburetion tests alone.

  5. Lazy throttle response throughout the rpm range as compared to the R1.

    The stock bike has lazy throttle response due to heavy slide springs that regulate the vacuum pistons (carburetor slides).

    • By clipping the springs to the desired tension, throttle response will become instantaneous and the delay on full throttle shifts will be eliminated. The result is a much more responsive engine.
    • By enlarging the slide's air displacement holes, you will be allowing them to lift and return quickly, to match the new spring tension, and provide the desired improved response.

In the UK, Ivan's kit can be obtained from the official importer, SG Motorsport.

Included with the kit are new main jets and new needle jets. Drill bits for drilling out the brass mixture screw plugs, slider holes, and pilot bypass holes are in the kit as is a screw to assist with pulling out the mixture screw plugs.

The price of the kit at this time is $120.

Here is a scan of the updated instructions provided with the jet kit.

To install the jet kit, the carburetor assembly must be removed. See Here.

Drill Out Mixture Screw Plugs:

This turned out to be very simple and took just a few minutes. Using Ivan's supplied drill bit, very light pressure, and a slow drill speed the brass just falls away. The plug actually just rotates right out as the bit bites into the brass. No need to use the supplied pull out screw.

When finished, turn the screws all the way in then back them out 3 1/2 turns to 4 turns. I have mine out at 4 turns.

From Ivan:

  • If you drill only one of the bypass holes (see below) the spec is 3 1/2 to 4 turns out.
  • If you drill both bypass holes the spec is 4 1/2 to 5 turns out (recommended) steady throttle cruising will be smoothest.
  • The mixture screws will not fall out at 5 turns. (any more is risky though)

When the 2nd pilot bypass hole (closest to the needle) is enlarged (see below), but not yet uncovered by the throttle plate, the larger hole acts as a bleed off and actually weakens the signal to the pilot jet which is why the screws need to be opened further. When the throttle plates open enough to uncover the two enlarged holes the extra fuel fills in the dry spot much better than with one hole enlarged. Fuel mileage should be better than with one hole enlarged because with two holes enlarged the throttle does not have to be opened as much to maintain normal cruising speeds. It gets enough from the idle circuits and does not need to draw from the needle.

Mixture screw plug drilling pics:

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Even after the carb assembly has been reinstalled into the bike, you may still adjust the mixture screws. You will need a long 90 degree slotted head screwdriver. A gear driven model is recommended for precise counting of turns. I bought the K&L part# 35-9653 for $44.95 available here. The slotted head is still a bit thick for the mixture screws and requires a few passes with a good quality file so it will fit in the slot. Use of this tool requires a good knack and some practice to actuate those hard to reach screws. For carb #1 you can use a regular screwdriver. But for carbs #2-#4 this tool is a must. Carbs #2 and #3 can be reached from the left. Carb #4 can be reached from the right and from behind avoiding the long protruding timing chain tensioner cap that gets in the way. You first have to engage the screwdriver into the screw slot. This is not easy. Turn the screwdriver wheel clockwise until you can feel the screw turning. If it is very quiet you can hear and perhaps feel the screw spring compressing. Do not try to engage the screw by turning counter clockwise. You may engage it without knowing it and inadvertantly unscrew the mixture screw all the way and watch it fall out when you retract the screwdriver. If it does fall out, you can just screw it back in though. To set the mixture screw out a fixed number of turns, it is recommended that you screw it in all the way first then back it out the desired number of turns. You will never be able to keep proper track if you try to adjust it from its current position given the difficulty of engaging the screw in the first place.

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Remove Float Bowls:

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The float bowl screws can be difficult to remove. Here is some sage advice from Bill Jinks.

The 4 bowls times 4 screws each = 16 cheap soft cadmium plated phillips head screws can become locked in place as the thread engagement areas suffer from varying degrees of dissimilar metal corrosion. To remove them without stripping out the heads:

  1. Turn your carbs upside down on a flat solid surface so that the screwheads are facing straight up.
  2. Insert your #2 phillips head screwdriver (firmly and squarely seated) into the screw head.
  3. With a mallet or block of wood give the top of the screw-driver several light but sharp raps. At this point, if you observe closely, you may see a very small puff of white dust emit from either end of the screw. This is the thread corrosion breaking free.
  4. With the bank of carbs held firmly in place (may require an extra set of hands) ALWAYS apply more downward force on your screwdriver than turning force and the screw should finish breaking loose and back right out. If the screw still demonstrates a great level of resistance, STOP! and repeat step #3. If you still manage to mangle the screw head all is not lost. Don't run out buying screw extractors and/or special left hand drill bits just yet, first try the following.
  5. Using a Dremel tool with a 1" diameter cut-off wheel (or a swiss slitting file) cut a common slot in the buggered-up screw head to accept a standard flat-blade screwdriver.
  6. Repeat steps 3 & 4 above.

Install New Main Jets:

Please note that the drawing on Page 7-8 of the Service Manual is an incorrect depiction of the location of the needle, pilot, and main jets.

FYI, the stock main jets are #132.5 for Carburetors 1 and 4 and #130 for Carburetors 2 and 3. Ivan's main jets are smaller, all #122.5 for both the slip-on and full system kit.

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Set Float Heights:

Mine are set at 13.5 mm but Ivan had since updated his recommendations. A range of 14 mm to 14.5 mm is now recommended with 14.5 mm being the target figure. Use 14.5 mm.

The carbs must be placed or held at the correct angle to properly measure the float height. The correct angle is that where the floats are just resting on the float pin without compressing the float pin spring.

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Measure the float height from the metal frame around the floats to the highest point on the float. If the line of sight makes it difficult to read the height for the center carbs with the ruler there is a special tool that permits a horizontal as well as vertical registration of the float height. Then you don't need a side view. You can set the height on the tool beforehand and then use it to check as you adjust by sliding it up and down over the float bowl and you don't need to horizontally eyeball it every time.

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If the two float sections for one carb appear to be at slightly different heights from one another they can be aligned to the same height with slight bending pressure applied carefully.

To adjust the float height, bend the tang on the float pin that holds the float pin spring as shown. Note that the correct angle at which to hold the carbs may change as the float tang is adjusted and the angle where the float just rests on the spring without compressing it changes.

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Owner's Association member Keith ("Chips Ahoy") made a vinyl template to make the float height measurement easy. The carbs must still be held at the correct angle but this eliminates any ambiguity about how to measure. The overall width of the template is 103mm, the opening is 53mm, the float height is shown as 14.5mm (critical dimension), the top is 15mm wide and 10mm high to clear the main jet, the overall height is 45mm.

Replace Float Bowls:

Make the screws tight without damaging the heads.

Remove Stock Needles:

The stock needle specification ID's are 5D129-3/5 for carburetors 1 and 4, and 5D130-3/5 for carburetors 2 and 3.

  1. Remove Carb Tops
  2. Pull out Diaphragm/Slider/Needle Kit Assembly
  3. Push Out Needle Holder and Needle Kit
  4. Disassemble Stock Needle Kit

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Drill Slides:

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Clip Slide Springs:

I clipped two loops (1/4 inch). Ivan now recommends clipping four loops (3/4 inch). The benefit is even more snap response. The downside is that full throttle openings from low rpm (~2200 rpm or so) will be much softer. This is an optional step and is a matter of preference. The springs can be removed and more clipped later without pulling the carbs if you're not sure how much to clip. I would go with Ivan's 3/4 inch recommendation.

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Install New Needles:

Ivan's needles are the same for carburetors 1-4 and feature a multiple taper design.

  1. Assemble new needle kit.
  2. Drop needle kit carefully in place in slide through center hole.
  3. Place needle holder (with needle spring attached) on top of needle and press down until it snaps into place. Make sure the needle assemblies are seated properly. You may feel them "click-in" when you push the needle holder/spring assembly back into the slide, but you have to make sure that all the legs that click in around the needle holder are seated properly. Just a click is not enough. Give each needle assembly a close examination to make sure they are not only clicked in but are fully seated as well. You'll know all the legs are seated properly when you can't see any of them bulging out around the needle holder assembly. In poorly illuminated environs you will need a light of some sort to see this clearly down the slide throat.

See addendum from Ivan at the bottom of this page if yours is a 2003 or newer model or if the white plastic spacers are not all the same thickness (height).

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To summarize the washer/spacer/eclip configurations, for the standard 2.5 mm thick nylon spacers, from the top of the needle:

  1. 0.5 mm washer
  2. eclip on 3rd position from top
  3. 2.5 mm nylon spacer

For the 3 mm thick nylon spacers the order from the top is:

  1. 0.5 mm washer
  2. eclip on 2nd position from top
  3. 0.5 mm washer
  4. 3 mm spacer

For those rare instances where one spacer is only 2 mm thick the order is:

  1. 0.5 mm washer
  2. eclip on 3rd position from top
  3. 0.5 mm washer
  4. 2 mm nylon spacer

Reassemble Carbs:

Note that if the carbs are not drained of gasoline immediately upon removal, the soft rubber diaphragms attached to the slides can stretch or swell and become difficult to replace back into the grooves of the carb body. This does not affect carb function but reassembly is made more difficult.

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Enlarge Pilot Bypass Holes:

Ivan now recommends, primarily for full exhaust systems, enlarging the rearmost (closest to the needle) bypass hole as well if sufficient smooth operation is not obtained by enlarging just the front bypass hole.

Note: Drilling depth is less than 1 mm for each hole.

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More valuable advice from Bill Jinks on this delicate procedure.

Do NOT divert from the recommended procedure of using a finger driven pin vise only! This procedure is very quick and simple and a finger driven pin vise is all you need. The drill bit is small and the amount of material you're removing is minimal. If you use any motorized device, even a Dremel or dental drill motor (which by the way is far too high-speed anyway) you will lose your feel and, more than likely, break off the slender drill bit.

  1. Lock the butterflys open so you can see all three pilot bypass holes and have a good line-of-sight for your drill bit to follow (you only open up the back two holes in each carb throat).
  2. With one finger applying slight pressure on the back of the free-rotating pin-vise head, use the fingers of your opposite hand to turn the pin-vise body clockwise.
  3. Don't try to go straight through in one shot. Every few turns stop and pull your drill out to clear/clean the metal chips from the hole and the drill bit flutes.
  4. As you come close to penetrating through the opposite side of the hole you will feel increased resistance almost as though the drill has come to a dead lock stop. This is because the drill is beginning to break through the other side of the hole. At this point you need to:
    • Stop.
    • Pull the drill out for one last clearing of chips and
    • Lighten up on the push pressure and increase the turn pressure and she'll pop right through without breaking the drill bit.
  5. Once through, give the drill bit a few extra free spin turns to clean things up a bit and make certain the hole is clear and break-through chip-free.

If you elect not to use the rag stuffed around the throttle wheel to hold open the butterfly valves and instead turn the idle speed adjustment knob then be careful and turn it back properly. Also, if you remove the idle speed adjustment cable, make sure that you thread it back properly so that it makes contact with the throttle on reassembly.


After reinstalling the carburetors, verify that the fuel petcock is in the ON position.

When bike reassembled perform a:

  1. Throttle Cable Adjustment
  2. Throttle Position Sensor Adjustment
  3. Carburetor Synchronization

My subjective impressions of the bike after installing the jet kit are:

  • the low end lost after installing the slip-on is back
  • the vibes are a bit less at all rpm but markedly less at high rpm
  • the 4-5K buzz was never really an issue for me and its still not noticeable
  • the power delivery is more linear and smoothly progressive
  • high rpm power was plenty scary before but now is even more so
  • runs cooler


From Ivan:

On the 2003 models, the factory has made an attempt at low speed mixture improvement. The white nylon needle spacers are not all the same thickness. Two of the needle spacers are 2.5 mm thick and the other two are 3 mm thick.

The needles on all previous model years use all four spacers at 2.5 mm. The needles themselves are still the same. They are just installed at different heights.

So what does someone do with a 2003 model when using my carb kit?

On the needles that have the 2.5 mm white nylon spacers, just run the 3rd clip as normal.

On the needles that have the 3 mm white nylon spacers, you will need to run the needles in the 2nd clip position (counting from the top of the needle) with one of the original 0.5 mm shims (previously removed) installed under the e-clip. This will give all the needles the same installed height. I have done all the measurements to verify this.

Addendum II:

From UK-based mikegtx2002 who has personally installed numerous Ivan's jet kits in this motorcycle. I thank him for his kind permission in allowing me to include these tips in this web page. See also his carb removal and replacement instructions.

Ivanís kit is a terrifically well developed product. In only wish I could say the same about the instructions that come with it. Thankfully we have Pat Glennís site to show us precisely what is entailed when it comes to modding the carbs. Between us I think we can guide you through the next stage without any difficulty.

First, get a clean, solid and well-lit work surface to operate on. A large square of clean cloth to rest the carbs on is a good idea, as it prevents little springs and washers from wandering off on their own. If the carbs are dirty, clean them off with a liberal dosing of WD40, a soft brush and a cloth. No need to be paranoid about this but small specks of dirt in the carbs can cause niggly problems later Ö

Setting the Mixture Screws

I start by setting the mixture screws first. In the UK we donít have to bother with removing the blanking plugs that our US cousins have inflicted on them by the Federal authorities. Just turn the screws in fully clockwise until they seat lightly. I use a fine marker pen to mark where the screw crosshead stops relative to the screw housing. That way I can be sure Iíve counted out precisely the right number of turns. Ivanís recommendation is between 4 Ĺ to 5 full turns out. Iíve always used 4 ĺ turns as a decent compromise and Iíve never had a problem reported back to me.

Drilling the Pilot Circuit Bypass Holes

Next I drill out the pilot circuit bypass holes using the smallest drill supplied in the kit. Make sure the bit is square and secure in the pin vice, with about 12mm of the bit protruding. Anymore and you risk the drill flexing and breaking. Too little will prevent you seeing clearly whatís happening at the cutting end when the tool is in the carb throat.

This is understandably the part of the job that worries most DIY mechanics but if youíre careful and donít force the pace, then thereís nothing to fret about. First, wind the idle screw in as far as it will go to open the throttle plates. Then, open the throttle plates a bit further until you can clearly see all 3 pilot circuit bypass holes. Jam the throttle plates open in this position with a rag stuffed into the throttle linkage. Make sure that the plates arenít going to snap closed while youíre drilling. Thatís the reason for also holding the plates open with the idle screw - insurance!

If thereís one picture from Patís site that you should print for reference, itís the one showing which holes you drill and the one that you leave alone. When youíre certain that youíre drilling the right holes, make your move!

Youíll find that you canít get a vertical approach to the hole with the pin vice. Donít worry, take the angle of cut as it presents itself and start to drill. I cradle the carb bank against the inside of my left forearm to keep it at an angle that lets me see what Iím doing. More importantly, it ensures that the carb bank canít move while the drilling is taking place. I turn the pin vice slowly in my right hand using just a light pressure. Let the drill do the cutting, you do the turning! Remove the drill a couple of times to clean off the swarf on the bit and in the carb throat. I use compressed air cans (the sort for cleaning computer keyboards and such) to blow the swarf away.

Note on Patís site he shows the pin vice angled in from the 2 oíclock position but the correct alignment is straight down from the 12 oíclock position. I suspect Patís picture is posed to illustrate the limited access and he needed to offset the tool for clarity [correct! :)].

People often wonder how theyíll know when the hole is completely drilled. Thereís a couple of giveaways. First, as you approach the point where the bit is about to break through into the chamber below the bypass hole, you will feel it get tight against your fingers. This is the time to be extra careful, as the twisting force on the drill is at its greatest. Be especially careful if itís cold in your workplace, as the drill may be a shade brittle at lower temperatures. The second indicator is that youíll feel the bit drop through the hole by about 1mm once the hole is opened out and clean.

Donít rush to extract the bit once you think youíve completely drilled through. Continue to rotate the pin vice for several turns until the hole is properly cleaned out and the drill bit will retract easily with a little rearward pull.

Be precise and patient with this part of the installation and youíve nothing to fear. For what itís worth, Iíve had 3 drills break on me in 100 installations. One was clumsiness on my part; one I put down to a brittle drill on a very cold day and I suspect the third was down to a manufacturing weakness in the drill itself. All 3 snapped off leaving plenty for me to grasp with needle nose pliers, and all came out without damaging the carbs in anyway. Lucky? Perhaps, but you make your own luck, I reckon.

Adjusting the Float Levels

Remove all 4 float bowls together. Donít do this one carb at a time, as youíll need to check that all 4 floats are at the same height. The screws are good quality stainless steel, but make sure your Ďdriver is a good fit. A poor quality, ill-fitting driver will still muller the screw heads. If the screws are tight, you may have a little corrosion in the threads. Some guys reach for the impact Ďdriver but thatís overkill. Seat the regular Ďdriver in the screw and tap the handle a few times with a hammer to break the corrosion. A couple of the screws sit underneath the spring clamps on the carb heater hoses. Donít disturb the clamps, just use a pair of needle nose pliers to lift the screws out, then wriggle the float bowls clear. Youíll also need to remove the idle adjuster holding screw from the middle of the No 1 float bowl.

As with all components removed from each carb, make sure you lay the float covers out so that you can refit them to the same carb later.

Patís site shows you clearly how and where to measure the float heights. However, gauging when the float is at the correct position for measuring isnít obvious from his pictures. Fortunately thereís a very reliable way of checking that youíre doing it right.

First, take the carb bank in your left hand and place one end on the workbench. You want the open float chambers to the right, so that you can get at them with your right hand. Obviously you reverse these directions if youíre a lefty.

Rotate the carb bank clockwise and watch as the floats fall away from the carb bodies. Once theyíve stopped moving, rotate the carbs back slowly in the opposite direction. Watch the floats carefully and youíll see them stop as they just make contact with the float needles. THIS IS THE POINT WHERE YOU MEASURE THE FLOAT HEIGHT. If you continue to rotate the carbs anti-clockwise, the floats will eventually move again as they overcome the float needle spring pressure.

Repeat this drill several times until you are confident that youíve got the right point of measurement. Hereís the reliable way of confirming that point. Measure the standard float height. I promise you it will be 12.5mm [or less :)]. Guaranteed. If you get a reading any different, youíre not measuring it correctly. Out of 400 floats Iíve checked, only one was out of adjustment - by a whole 0.5mm.

Once youíve established the datum for adjusting the float heights, the rest is pretty easy. You need to bend the float tangs down by about 0.5 - 0.75mm to increase the float height to 14mm as recommended by Ivan. The actual outcome of increasing the measured float height is to reduce the fuel level in the chamber, which is what we want.

Again, if you need to bend the tangs more than the amount above to get a 14mm float height, youíre probably taking your measurements incorrectly.

If you sight along the line of all 4 floats, you should see them lined up at the same height. I use the moulded ridge around the edge of the floats as my reference for this and itís obvious when thereís any deviation between adjacent floats. Keep making small adjustments until you have all 4 floats at the same height, between 13.5 - 14mm.

I found this to be the most time consuming part of the installation, except on those days when the magic was upon me! On those occasions, I got the bend of the float tang perfect on each carb first time. It didnít happen often, though Ö

Changing the Main Jets

The next bit is easy. Remove the OE main jets and replace with Ivanís mains. Simple as that. Just remember that youíre tightening brass components so donít be brutal. Use a crosshead Ďdriver that fits properly and just nip the jets up in the holder. Youíll need a spanner on the holder to stop it unscrewing from the carb body as you remove the OE mains.

Give the float heights one final check and replace the float bowls. No need for gasket sealant, just tighten the screws and replace the idle adjuster cable.

Needles and Springs and Things

Flip the carbs and remove all 4 of the carb tops. Watch out for the spacers under the TPS cable holder screw and the choke mounting screw. Lay the carb tops out in sequence for refitting to the correct carb later. Check to see whether the small O-ring has remained on the carb body or is stuck to the carb top. Put it safe for refitting.

Extract the springs and the slides. Remove the needle assemblies from each of the slides. See Patís site for illustrations. I use a pair of needle nose pliers to grip the needle holder. Watch out for the needle springs as you extract the needle assemblies.

Lay out each set of components neatly corresponding to the carb they came from. Using the medium sized drill in the jet kit, enlarge the air bypass holes in the throttle slides. Note that only a very small amount of swarf comes out, as this is only a minor enlargement. Donít drill out the hole that the needle fits through.

Replace the OE needles with Ivanís using Patís site for reference, noting that on pre-2003 bikes you omit one of the OE shims on each needle.

From 2003 onwards, Yamaha changed the size of the nylon spacers on the needles. Pre-2003 models have 2.5mm spacers on all needles, but later machines usually have 2 x 2.5mm and 2 x 3.0mm spacers.

I say Ďusuallyí for a reason. For a start, I have found the mixed spacer combination on a late 2002 model year bike. More frequently, Iíve come across late 2003 and 2004 machines that have 3mm spacers on all 4 needles. So, I suggest you need to check the spacer size irrespective of the model year.

The procedure for getting the correct installed needle height with 3mm spacers is simple. Move the e-clip on Ivanís needles from the 3rd groove to the 2nd groove from the top. Put the nylon spacer under the e-clip, then one of the OE metal shims under the nylon spacer.

Follow Patís directions for refitting the needle assemblies. I use the needle nose pliers to insert them back into the housing, being careful to ensure that they fit squarely in the slide. It will be obvious if the needle holder is off centre in the housing. If it is, remove it and try again. Note that there are splines on the needle holders that correspond to cut-outs where they fit in the slide body. Push the needle up to check that the spring is correctly seated. It should move about 2-3mm or so.

If youíve encountered different sized spacers on your needles, itía good idea to check that all 4 needles are installed at the same height before you refit the slides. Measure with a gauge or ruler.

Once all 4 slides have been drilled and the needles changed, refit the slides to the carbs and set aside while you clip the slide springs.

I use a carpentersí 90 deg adjustable measure as a jig to give me the correct spring length. Patís site gives good guidance on this, so thereís little for me to add on the technique. However, there has been some debate about the amount to clip off.

Ivan says ĺ" but Iíve taken a little less on most of my installations. Typically I take Ĺ" off, which gives a final cut length of 3 3/8". I prefer to err on the slightly long side, rather than end up with a spring that is too short. If the spring is too short it can lead to the slides Ďbouncingí in the carbs causing inconsistent fuelling.

Whatever method of measuring you choose, be sure to get the springs the same length as each other. Place them alongside each other on a flat surface to check this.

Once youíve cut the springs, refit them to the carbs and replace the carb tops. Be sure that the carb diaphragms are seated correctly in their grooves and donít pinch them when refitting the carb tops. Donít forget the little O-rings either, and remember the 2 spacers for the TPS and choke mounting screws.

When the carbs are back together, push each slide up inside the carb throat using your fingers. Make sure that it moves all the way to fully open and doesnít bind at any point. You should note the same resistance and each slide should return at the same rate. If it doesnít, youíve probably got a spring binding or a pinched diaphragm.

Well done - youíve now got a set of ĎIvanisedí carbs ready to reinstall in the bike. Time for another coffee break. Then go back and reinstall the carbs.

Addendum III:

After having let my bike sit for some time I proceeded through the list of things you have to do and check before riding the bike again. One of those things is to check the carbs particularly the needles and floats. Old gas can clog up the needles and it's a good idea to pull the carbs and make sure the needles and float bowls are clean and the float heights are correct. I did this and even though the gas looked and smelled good even after years of sitting I let the needles soak in carb cleaner for a while. After reinstalling the carbs and making sure the bike was ok to start I did start the bike but it ran very poorly, would not idle, leaked gas all over the place, and would not restart after shutdown. I saw that there was a lot of fuel seeping out from the float bowls.

So I pulled the carbs again and checked the rubber gaskets that seal the carb float bowls. They were old, dried out, and brittle so I changed them all with four new ones. They are about $6.00 each from various sources. Now a new gasket will not stay inside the channel on the float bowl so when reinstalling the float bowl you have to lay the gasket down on the carb mating surface and carefully replace the float bowl over it so that the gasket is placed inside that channel and the bowl seats correctly before screwing it back down.

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After changing the float bowl gaskets and installing the carbs I tried again to start the bike and it still ran poorly but no fuel was leaking from the bowls. After a short time I could see fuel dripping under the bike. Checking the source revealed that the carbs were still leaking fuel out one of the two overflow/vent hoses attached at the top of the carb bank.

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Some research on the FZ1OA message board led me to the possible time disintegration of the o-rings that seal the float needle assembly in the carb. My thanks to FZ1OA member eskort for starting the thread that put me onto these o-rings that solved my fuel leakage problem. If this o-ring is not doing its job then fuel can leak around the float needle assembly directly into the carb filling it with gas and eventually leaking out the top of the carb down those vent/overflow hoses. This floods the carb causing the poor running and the no restart problem I had experienced. From Yamaha you have to order the entire float needle assembly but you can get just the o-rings from McMaster-Carr. The cost is about $6.00 for 100 o-rings plus shipping. You will only need four. The package states that the shelf life is 15 years. My bike is 15 years old. In service the life of these o-rings must be much less, perhaps half that.

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To access those o-rings you have to remove the float needle assembly on each carb. Remove this Phillips screw. Note how it is holding down the roller pin in its slot so you can then reassemble it the same way. The screw is soft brass so use a quality screwdriver and good technique so you don't mangle the head.

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Next, pull out the floats, float needle from its holder, float needle spring, and roller pin as an assembly. Do yourself a huge favor here and be careful so you don't drop or lose track of any of these tiny parts.

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Next, remove the tiny screw holding down the float needle holder. Once this is removed you can pull out the float needle holder. The friction felt as you pull it out is the o-ring providing the seal that keeps the fuel from flooding into the carb and float bowls.

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This is the float needle holder. You must replace the o-ring around it with a new one. I used a pair of tweezers to grab the old ring and pull it up and out. They were all so brittle that they immediately split. The new ring will stretch a bit so you can slip it over the screen side of the holder and into its proper position. Note when you reinsert the holder that you feel some friction. When you place the float assembly back make sure the float needle slides into the shaft in the holder and that it dangles from the adjustment tab with that tiny little spring. Again make sure the roller pin is in its slot so that the float assembly attachment screw holds down the pin.

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Here is a problem I ran into. The float needle holder hold down screw for carb number three had its Phillips head mangled at the factory. This is the first time it saw the light of day since then. As you can see in the first photo no Phillips screwdriver would bite into it enough to permit its removal. Fortunately, at some time in the past I had picked up a set of Craftsman damaged head removal tools. These are made of sharpened hardened steel and they cut into the soft brass screw head so it grabs and turns the screw. So that I could then still reuse it (because it is a highly specialized screw that would have had to be ordered) I held it in a pair of pliers and cut a slot into the head with a hacksaw blade so that a flat head screwdriver could be used to tighten it.

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All four of my o-rings were shot and leaking some fuel. When all the new o-rings are installed check the float heights again. In the second photo I have removed all coolant hoses from the carb bank as they are no longer used having performed the carb coolant bypass mod.

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These o-rings were indeed the reason for the gas leakage. With new o-rings there is no more fuel dripping out those vent/overflow hoses.

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Last Updated: 12-15-2016

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The information presented here reflects solely my personal experience with my motorcycle and is presented for entertainment purposes only. No information presented here is to be relied upon for issues of rider safety nor to replace the services of a qualified service technician. Any attempts to follow or duplicate any of these procedures are done so completely at your own risk. By reading the information on this site, you agree to assume complete responsibility for any and all actual or consequential damages that may arise from any information presented herein.