I start by setting the mixture screws first. In the UK we don’t 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 I’ve counted out precisely the right number of turns. Ivan’s recommendation is between 4 ½ to 5 full turns out. I’ve always used 4 ¾ turns as a decent compromise and I’ve 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 what’s 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 you’re careful and don’t force the pace, then there’s 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 aren’t going to snap closed while you’re drilling. That’s the reason for also holding the plates open with the idle screw - insurance!

If there’s one picture from Pat’s site that you should print for reference, it’s the one showing which holes you drill and the one that you leave alone. When you’re certain that you’re drilling the right holes, make your move!

You’ll find that you can’t get a vertical approach to the hole with the pin vice. Don’t 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 I’m doing. More importantly, it ensures that the carb bank can’t 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 Pat’s site he shows the pin vice angled in from the 2 o’clock position but the correct alignment is straight down from the 12 o’clock position. I suspect Pat’s picture is posed to illustrate the limited access and he needed to offset the tool for clarity [correct! :)].

People often wonder how they’ll know when the hole is completely drilled. There’s 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 it’s cold in your workplace, as the drill may be a shade brittle at lower temperatures. The second indicator is that you’ll feel the bit drop through the hole by about 1mm once the hole is opened out and clean.

Don’t rush to extract the bit once you think you’ve 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 you’ve nothing to fear. For what it’s worth, I’ve 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. Don’t do this one carb at a time, as you’ll need to check that all 4 floats are at the same height. The screws are good quality stainless steel, but make sure your ‘driver 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 ‘driver but that’s overkill. Seat the regular ‘driver 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. Don’t disturb the clamps, just use a pair of needle nose pliers to lift the screws out, then wriggle the float bowls clear. You’ll 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.

Pat’s site shows you clearly how and where to measure the float heights. However, gauging when the float is at the correct position for measuring isn’t obvious from his pictures. Fortunately there’s a very reliable way of checking that you’re 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 you’re a lefty.

Rotate the carb bank clockwise and watch as the floats fall away from the carb bodies. Once they’ve stopped moving, rotate the carbs back slowly in the opposite direction. Watch the floats carefully and you’ll 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 you’ve got the right point of measurement. Here’s 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, you’re not measuring it correctly. Out of 400 floats I’ve checked, only one was out of adjustment - by a whole 0.5mm.

Once you’ve 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, you’re 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 it’s obvious when there’s 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 didn’t happen often, though …

Changing the Main Jets

The next bit is easy. Remove the OE main jets and replace with Ivan’s mains. Simple as that. Just remember that you’re tightening brass components so don’t be brutal. Use a crosshead ‘driver that fits properly and just nip the jets up in the holder. You’ll 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 Pat’s 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. Don’t drill out the hole that the needle fits through.

Replace the OE needles with Ivan’s using Pat’s 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 ‘usually’ for a reason. For a start, I have found the mixed spacer combination on a late 2002 model year bike. More frequently, I’ve 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 Ivan’s 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 Pat’s 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 you’ve encountered different sized spacers on your needles, it’a 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 carpenters’ 90 deg adjustable measure as a jig to give me the correct spring length. Pat’s site gives good guidance on this, so there’s little for me to add on the technique. However, there has been some debate about the amount to clip off.

Ivan says ¾" but I’ve taken a little less on most of my installations. Typically I take ½" 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 ‘bouncing’ 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 you’ve 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 don’t pinch them when refitting the carb tops. Don’t 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 doesn’t bind at any point. You should note the same resistance and each slide should return at the same rate. If it doesn’t, you’ve probably got a spring binding or a pinched diaphragm.

Well done - you’ve now got a set of ‘Ivanised’ carbs ready to reinstall in the bike. Time for another coffee break. Then go back and reinstall the carbs.