Scott R. Nelson
8-August-2000
The proper jet kit for a 1997 M900 (actually 93-98) is the "CRB-D12-1.1-ti Ti ProKit" which includes the following;
The only ones you can't get directly from Mikuni are the needles and springs. The needles are significantly different from the originals with much more taper.
I had originally intended to desmog the bike at the same time, but decided against that because I didn't want an extra variable in case the bike didn't run right afterwards.
The following steps are slightly revised from the order I took my bike apart and installed things. Knowing all of the steps, it is obvious that some things can be done earlier and will simplify other steps. For example, to get the airbox off, I just kept loosening things until it would finally come off. I wrote down all of the steps to make sure I put everything back in the right order. It was worth the extra trouble.
Park the bike where you can work on it for a few hours undisturbed. You might want to spread a cloth underneath it to make it easier to catch dropped parts. I put an old bedspread under mine and it helped. I also set up a card table to put all of the parts on. That kept me from stepping on things or accidentally kicking something out of the way.
It's a bit easier if the bike is on a rear stand rather than just the side stand. It is more stable and everything is horizontal. If you have a bike stand, use it. All references to left and right are relative to when a rider is sitting on the bike, ready to ride.
Tools needed: 8mm, 10mm, and 12mm open end wrenches. 5mm and 6mm allen wrenches. Medium phillips and small flat bladed screwdrivers. 8mm and 10mm nut drivers. Some clean rags. A small steel ruler with a T-shaped adjustable mark or some other way to measure float height. Spray carburetor cleaner. An electric drill.
1. Remove the seat and raise the tank. Use that little rod on the left side to hold it up. There is no need to remove the tank.
2. Drop the oil cooler down below the level of the front fender and leave it there until everything else is back together. You need it out of the way to get to the other things. Take the mirrors off too, since they'll just be in the way.
3. Remove the airbox top and filter. It's easier to pull them both off together rather than to pull off just the top and then the filter. Don't drop any of the clip pins. Use two hands to remove each clip and pin.
4. Remove the ignition switch so that the airbox will come out of the frame. Remove the plastic cover over the ignition switch, then using a 6mm allen wrench and a 12mm wrench, remove the bolts holding the switch in place. Move the ignition switch over to the side, out of the way.
5. Unplug the two positive battery connections from the connector on the main positive wire. This works better than disconnecting the battery at the battery terminal. (I've tried it both ways.)
6. Remove the 10mm nut for the negative connection underneath the battery box, remove the 2 wires and the gold colored wire that holds the air breather hose in place. Take a good look at how that gold wire piece is placed so that you can get it back the same way.
7. Disconnect the clear battery overflow tube, unclip the two rubber straps, and remove the battery. Put it somewhere out of the way.
8. Remove the two allen head bolts under the battery and the one 8mm bold under the front of the airbox.
9. Loosen the two hose clamps connecting the carburetor intakes to the airbox.
10. Disconnect the big hose from the airbox to the canister at the back of the bike. It's easier to disconnect at the back than at the front.
11. Pull off the starter relay under the battery case. Be careful to not unplug the wires from the ignition, or at least be aware if you do. I didn't realize that I had disconnected those wires and had to undo some of the reassembly to be able to plug the wires back on.
12. Disconnect the tube at the bottom front of the airbox that goes down to the bottom of the frame. This is easier to disconnect at the bottom by sliding the rubber grommet out of the holder, assuming you intend to put it back afterwards.
13. Unbolt the coil assembly from the airbox.
14. Unhook the 30A fuse on the right. This is easiest if you pull off the clear cover and pull out the fuse. Then insert a flat screwdriver into the back to release it and pull the assembly up.
15. Remove the airbox.
16. Pull off the two tubes going to the grey plastic thing on the right side of the bike.
17. Loosen the top hose clamps under each carburetor.
18. Pop the carburetors loose. If you are capable of setting the float height with the carburetors on the bike, you can skip the steps involved in removing them from the bike. Everything else could be done with the carburetors on the bike, although it might be a bit hard to see some of the smaller parts. (Reconnecting the throttle cables can be tricky.)
Stuff rags into the intakes to keep any dirt out of there.
19. Disconnect the choke cable. An 8mm nut driver works better than a screwdriver for this one.
20. Disconnect the tube from the middle of the carburetors to the grey plastic thing on the left side of the bike.
21. Disconnect the two overflow tubes on the bottom of the float bowl. Your fingers should be strong enough to remove the clamps. Remember which of the two connections these tubes came off of.
22. Disconnect the fuel line from the fuel pump.
23. Drain the float bowls using an 8mm nut driver or any screwdriver on the bolt at the bottom of the float bowl. You might want to use those overflow tubes to direct the gasoline to a proper container.
24. Remove the float bowls, or at least the two screws holding the throttle bracket in place. One of the 8 screws on my bike was buggered up. I don't know if that was done at the factory or at my 6000 mile tune up.
25. Disconnect the throttle cables by sliding each cable out of the slot that holds the end of the cable. Look closely at how they're positioned, because this was the hardest part for me to get back in place. You might consider just dealing with the carburetors with the throttle cables still connected. If you don't loosen any of the bolts holding the throttle cables to the throttle bracket, you can keep your original settings.
Finally, you can start doing something with the carburetors.
I set the float height first, but I would recommend doing that last, after you're through banging into the floats half a dozen times.
1. Using a very small flat screwdriver, remove the pilot jet. It's down in a hole a little ways, right next to the main jet and the other jet marked "70". My old pilot jet was a 37.5 and the new one is a 42.5. They were shaped a little different from each other, but obviously work the same way. Put the new one in and tighten snugly, but carefully.
2. Remove those two jet thingies marked "70" and the little brass arms holding the main jets in place, then pull the main jets out with your fingers. Twist a little if you have to. They're just held in by a rubber O-ring. My old mains were 142.5 and the new ones were 145. It was a real dilemma whether or not I should go to 155, but I felt it would be easier to detect a lean condition and I wasn't going with a fully open airbox anyway.
Put the O-rings on the jets you'll be reinstalling and push them back into place. You may have to do some twisting to get the jets back in all the way. Make sure the O-rings go down into the holes. Tighten the screw/jet thingies marked "70".
Do not remove the 8mm brass screws that cover up the needle emulsion tubes unless you will be replacing those tubes.
3. Remove the big black covers from the side opposite the float bowls to expose the CV (constant velocity) section. Remove the old springs and put the little plastic pieces onto the new springs. Carefully pull out the slides, remove the needles, and replace with the new, much pointier needles. There is a stainless steel washer, a nylon spacer, and a circlip on the needle. The circlip can be removed with a small screwdriver. The nylon spacers were very difficult to get off and to get back on the new needles. Be patient and don't bend those needles! I considered drilling the centers of the nylon washers slightly to get them back on.
I started off with the circlip on the #3 (middle) position. The jet kit came with a set of 8 new circlips, although only two are needed. The new ones may not be as high of quality as the old ones, so you might consider just reusing the originals. I have 8 spares now.
4. Drop the needles into place in the slides, making sure the metal washer and the nylon washer are on the pointy side of the needle and that the nylon washer is snug against the circlip.
5. Carefully reinstall the slides into the carburetors, lining up the needles as they drop through. If your bike has very many miles on it, check the "emulsion tubes" that the needles slide into to make sure they're still round (you'll have to remove those 8mm brass screws I previously said not to remove, to do this). Mine looked good.
6. Install the spring, being sure to line up the plastic end-piece with the needle. Put the black cover back on. I intended to use the new 16mm hex-head screws here, but I couldn't get the washers off of the old screws so I just used the old screws. The philips screws work better here than for holding the float bowls on anyway and I found a use for two of the 16mm screws when I put the throttle bracket back into place.
7. Set the float height to 14mm. I called Factory Pro and they said to rotate the carburetor until the floats are hanging free, then back just until they touch. If you rotate them more, they'll compress the small spring in the float valve and you'll get an incorrect measurement. Be sure to measure from square side of the float rather than the more pointed side. The measurement is made from the float bowl surface to the part of the float furthest away from the surface. Note that the float is at more than a 45 degree angle to the measuring surface. My floats measured 9mm, which is why I felt the need to call Factory Pro to make sure I was measuring from the right place.
To adjust the float height, pull the pin that the float pivots on, then bend the metal tab that pushes against the valve that stops the gasoline from entering the carburetor. Small adjustments can be made without removing the float. You don't have to bend the tab by much to make a big change in float height.
8. Reinstall the float bowls using the new 5 x 12mm hex head screws. But first, spray some carburetor cleaner in the float bowls to get rid of any fine residue that has collected there. Every motorcycle I've ever owned with a few thousand miles on it has had some kind of residue in the float bowls. Use the two longer 5 x 16mm screws for the throttle plate because the 12mm screws are too short. Don't forget to put the throttle plate on. Gently tighten the screws a little at a time until the float bowls are snug. Remember that this would be a very bad place to strip a thread.
9. My bike still had the brass inserts covering the mixture adjusting screws, so I had to remove them. They're located right next to the float bowls on the tube-shaped piece that is in the way when installing the float bowls. You can see a matching hole on the carburetor intake that lines up with it.
What worked well for me was to use a very small bit to drill the center, then about a 3/16" bit to get them out. Don't go in more than 2-3 mm with the small drill or you'll be drilling on the mixture screw itself. Also remember that brass is quite soft and drill bits cut into it very quickly. To remove the inserts, I drilled with the 3/16 bit until the bit grabbed, then it spun the insert and I was able to gently pull it out as it was spinning. There may be a better way to remove the brass inserts, but this worked for me.
10. To check the previous setting of the mixture screws, I suggest a screwdriver marked on one side. I got mixed up counting half-turns to find out what the old settings were. I think they were both 3 1/2 turns out. Set the mixture screws to the desired setting. I used the recommended 3 1/2 turns out.
1. If you completely removed the carburetors from the bike, put the throttle cables back in place. The cable that "closes" the throttle is harder to get in place than the one that opens the throttle, do it first. After quite a bit of struggling here, I got it into place only to find I had put the "open" cable into the "closed" position. Double check this first. I think this is actually the point when I tightened down the float bowls. I hope you don't keep reinstalling and removing the float bowl screws like I did.
2. Remove the rags from the intakes, feed the carburetor assembly back through the frame, and push them into place in the rubber connectors. Make sure all hose clamps are in place. Tighten the clamps on the intake runners.
3. Put the fuel line back on the fuel pump, under the frame tube, and tighten it.
4. Put the overflow tubes back on the carburetor float bowls. Make sure they're on the opening without the drain screw.
5. Reconnect the two tubes to the right plastic grey thing.
6. Put the two hose clamps in place and install the airbox.
7. Clip the 30A fuse back in place on the right side of the airbox.
8. Bolt the coil assembly back into place.
9. Reinstall the tube from the bottom of the airbox.
10. Lift up the airbox and put the starter relay back into place, under the battery holder. Make sure the small 2-wire connector is attached to the relay.
11. Put the top hose clamps in place and attach the airbox to the carburetors.
12. Put back the 3 airbox screws and bolts.
13. Reinstall the battery. Reconnect the positive wires. Put the gold colored wire and the two negative wires back in place and tighten the 10mm nut. Be sure the gold wire hooks around the breather tube to the carburetor to hold it out of the way of the choke mechanism.
14. Put the ignition switch back into place.
15. Reinstall the air filter and airbox lid. Pull out the two rubber snorkels if you're keeping the standard lid.
16. Put the oil cooler back into place.
17. Lower the fuel tank back into place, reinstall the seat, and you might be done.
You'll have to crank the engine for a while before enough fuel is pumped into the float bowls to make a proper air-fuel mixture. Make sure you don't crank the engine for more than about 10 seconds before waiting a little bit. Mine took more than 20 seconds of overall cranking before it finally started.
Go ride it and try to figure out if it's running right at all different speed ranges. Factory Pro offers many good hints as to what adjustments to make and how to tell what is needed.
Changing the idle mixture screw adjustment to 4 turns out rather than 3 1/2 makes it run better when cold and improves the transition from no throttle to part throttle.
Later testing showed that the bike pulled strongest at high rpms with only one of the two snorkels removed from the airbox. Looks like the main jet should either be a 155 or maybe a 150.
Wow, I really don't get around to updating this, do I?
A few months ago I cut open the airbox to give about 30 square inches of opening and switched to a 155 main jet and it all runs very well, I also dropped the needle one notch from the middle to lean out the midrange just a bit. The idle mixture screw stays at 4 turns out.
With this setup the plugs are the right color and it runs smoothly nearly all of the time. When the temperature gets into the 90's I can tell that it's just a touch rich but it is not a significant problem. I don't have to let it warm up for more than about 30 seconds before I can turn the choke off and ride it away, probably due to the mixture screw setting.