Beginning the CB900C Carb Rebuild

It’s been a while since I’ve done some work on the bikes (winter time projects were in the way).  Bringing the CB900C back to the middle of the garage, I fueled her up to see where the project was left off.  Engine started after a bit but still running rough.  Taking some quick temps, I noticed that the header off of cylinder 4 was much colder than the other 3, so it’s time to pull the carbs, give them a clean, and see what’s really going on.

After pulling off the carb pack, I started breaking things down to single carbs.  After stripping a few of the screws on the braces I finally started getting into the single carbs but needed to break for the night.  Found a great reference for breaking these carbs down here:

Definitely will be making my way through that document in hopes of getting them back together.  Will post more and pictures as the project continues.

1979 CX500C, time to sell it!

Well the CX500C is finally completed. It’s time to put it up on the block for sale. Here’s some parting shots of it before I let it go to the next owner


So form the last set of pictures a few changes, header wrap, cleaned =)

Yamaha Petcock Partial Rebuild

After getting the prettied up tank onto the XS400 we found a fuel leak.  At first the theory was a leak up around the mount point of the petcock, but further investigation found that it was a passage way on the diaphragm assembly that was causing the problem.

It’s difficult to see from the image, but the diaphragm is all on the outside (right-side in the picture).  This was basically allowing fuel to make its way to the passage and puddle onto the bike.  Taking the vacuum side apart wasn’t too difficult, just four screws.
Basically you’ve got the diaphragm block, diaphragm, spring and the valve cover.
The diaphragm is actually made up of two thin sheets, each goes on one side of the diaphragm block.
The piece put back together, now the diaphragm is covering both sides and should be good to go.  All reassembled it’s hard to see the overall difference, but having the diaphragm on both sides did the trick.
No more leaks, at least not from the petcock.

Paint day for the CX500 side panels and XS400 body parts

Finally got the CX500 side covers painted, I’m really excited as this is the last major bit of the puzzle on this bike

We also managed to get the XS400 tank, starter cover, and side covers painted. They’re a really neat burnt copper finish and should look great on this ratty old bike

Quick update on the XS400

Today after work I put a spare fuel bottle on the bikes and filled the carbs for the first time since they were rebuilt. Plugged it all back in and fired it up.

After a quick vacuum balance with my DIY manometer the thing was running pretty good. I still have a bit of a idle down lag at 3K rpm’s but it’s a whole lot better than when I got the bike (or before I vacuum balanced the carbs).

I’m still working on getting the tank and fenders completed, but as it stands now, with the temporary fuel bottle hooked up, I can actually ride the thing around and get an idea as to it’s overall performance.


XS400 and CB900 tanks stripped and ready for more cleaning

Well I managed to get the XS400 and CB900 tanks stripped down. On the XS400 tank there is a bit more work to remove some of the more stubborn paint around the lip but that shouldn’t be too bad. This weekend I’m hoping the new charger arrives so I can strip the inside of the tanks next.


BS34 carb pack back together for the XS400

Today I finished reassembling the BS34 carburetor pack for the XS400 project, it came out pretty well.

Upon disassemble I noticed that the right side carburetor main jet was completely turned out and sitting loose in the threads at the bottom of the bowl.

On the left side the float valve housing was loose because it’s O-Ring had failed.

Both carburetors got a total top to bottom internal cleaning with the ultrasonic.


Fork seal job for the XS400 (reassembly)

Hi Folks,

Well I had a bit more time over the weekend to complete the fork seal job. I cleaned and polished all the critical bits, inspected the springs and pilot holes. the bits that needed it went into the ultrasonic cleaner and everything was well dried before any further work took place.

Once I had finished the bits I made sure to lay everything out on my work table to ensure all parts are still present and available. Some bits got reassembled right away, such as the nylon slides on the damper spindles and the bleeder screws on the main fork tubes (I didn’t want to lose these tiny parts):

So now that we know everything is still here, step one is to lock the fork tube into the vice and insert the seal seat:

Once the seat is reinstalled the next step here is to use a small amount of rubber safe heavy grease around the inner fork tube were the oil seal will mate with the metal. This is useful in reducing binding of the rubber while you’re driving the seal down into the fork tube:

Again, a little bit goes a LONG way and we don’t want globs of this stuff in the fork tube.

Next set the oil seal back into the fork tube. Make sure that the sealed side (the solid side) is always up. Carefully press the seal in by hand as far as you can go. Make sure that it seats evenly.

Once pressed in as far as you can get it by hand use your fork seal driver and a hammer to set it the rest of the way down. It should seal past the seal locking spring groove. In my case I used a bit of PVC piping that just happened to be exactly the right size for 33MM fork seals:

As you can now see from the image blow, the seal is seated far enough down that the locking spring can cleanly snap into place:

The next step is to install the new dust wiper, you could do this after you reassemble the shock more completely however I’ve found with the “inner” style wiper, it’s a lot easier to drive it into place without the inner tube assembly in place:

All done with the lower fork tube at this point. Now we need to reassemble the inner tube assembly. Below is an image of how this assembly will look once fully installed within the fork tube:

Note that the shiny aluminum part on the top (the taper spindle) will NOT be on this assembly while I’m setting it into the inner tube assembly. Prior to inserting the bottom end (the non-spring side) into the inner tube assembly it should look like this:

Next guide the damper spindle, and rebound spring into the inner tube assembly. I use an old wire hanger to push this through as the nylon guides will tend to stick a bit, however the main spring works just about as well to guide it in. Also, you’ll also want to do this while the tube is laying down as it makes it MUCH easier to keep the springs in place as well as threading the spindle through the lower inner tube assembly:

Once threaded through successfully reinstall the taper spindle:

Now reposition the lower fork tube so that it’s clamped horizontally. After that carefully guide the inner tube assembly into the lower fork tube:

Next temporarily insert the main spring down the inner tube assembly:

Using the main spring to keep the damper spindle in place, thread the damper spindle / rebound stay bolt back into the bottom of the fork tube. At this point you should be able to get this threaded with out much problem. Use the spring to apply pressure so that the threading is assured.

Using a lot of pressure on the main spring, perform the final tightening of the damper spindle / rebound bolt. Refer to your manual for the exact torque values, in my case it said “tight” which I took to mean around 15lbs or so. The manual also recommends using a thread locker, however I find this unnecessary and problematic in the future if you need to get back in there.

Once tight, reposition the now nearly complete assembly in the clamp so that it’s held at a mostly vertical angle

Now measure and fill the fork tube with oil

Now slowly insert the main spring back into the inner tube assembly. Remember you don’t want to yank it back out again as it’s covered in oil. Also note that on progressively wound springs the tighter windings need to go to the top of the shock assembly

Once inserted all the way you’ll notice a bit of the spring still coming out of the inner tube assembly. If it’s much more than this try tugging on the inner tube assembly so that it’s all the way extended

Now set the cap back on the top of the spring and using a Phillips screw driver, plunge the cap all the way back down into the inner fork tube. You might need to grab the inner fork tube to prevent it from depressing back into the lower fork tube. Once seated you should be able to get the inner fork tube plug stay spring into it’s slot, this will lock everything back into place

The last step is to reinstall the black rubber cap on top. After that reinstall the fork tubes back onto the bike and enjoy your now non-leaking and much safer suspension setup.

Fork seal job for the XS400 (disassembly)

This weekend I decided since it was shitty and snowy out side it would be the perfect weekend to do the fork seals, the ones on the bike now are clearly shot with very little oil in them and zero rebound control (which makes for a dangerous ride).

I started by removing front wheel, after that the top triple tree had to go. Normally this isn’t required however on this bike the pretty chrome pieces completely obscure the lower fork clamp bolts, so the only option was to remove the top triple tree then slide the chrome out of the way. Once done the lower bolts where easily accessed and the fork tubes slid right out.

Once off the bike I prepared a work space on my bench. You’ll want to lay down heavy paper (in my case paper yard bags over a large table, this is because the remaining oil in these forks is pretty nasty. In many cases the older Japanese bikes used a type of fish oil, it has a very unique smell and you’ll know it when you get it.

You’ll want to have the following tools and parts available BEFORE you start:

  •  Small flat blade screw driver to pull the seal springs
  • Phillips screw driver (#2 should be good)
  • Large flat blade screw driver to pull the seals (Or better custom seal puller)
  • Heat gun to soften the old seals
  • Impact gun or breaker bar with long shaft hex socket to pull the lower fork rebound / drain bolt
  • New fork seal kit with dust wipers (chances are the wipers are shot)
  • New fork oil (on these older bikes I like 20w)
  • Large vice to hold the parts with
  • Cloth to prevent damage to the parts while in the vice
  • Loads of paper towels
  • Vinyl gloves (this will be messy)
  • Oil drain can for the old used fork oil
  • A few cans of heavy duty engine degreaser
  • Something to measure out the proper amount of fork oil
  • Factory service manual

So lets get started. As you can see from the below picture of the dust cover and inner wiper seal these are shot and need to be replaced. The tell tail signs of these are grease / oil on the fork shaft it self, in this case we can see water there as well

So first things first, lets drain this thing. Start by clamping the lower fork assemble in your vice, then using your long shaft hex socket and impact gun remove the lower rebound / drain bolt.

Once complete I was able to slide the inner fork assemble out without problems, however there was lots of oil so the first thing I did was set them on my oil catch and let them sit for a few minutes. A quick squirt of engine degreaser helped speed along the process

After it had a bit to drain it was time to pull the old, and failed inner seals. To make my life easier (which I’m always all about) I fashioned a custom tool out of a thick bit of scrap reenforcing steel I had laying around (the last time I did a fork seal job). I ground it down all the way around then cut a lip into it. I did this all with the bench grinder and it took me all of 20 minutes or so, you can of course use a large flat blade screw driver, however this beast is MUCH stronger and won’t scuff or slip on the seal:

The next step is to get out the heat gun, you’ll want to heat up the top of the fork seals until they’re nice and warm. I always look for a slight bubbling around the seal, that indicates that the glue (yes sometimes they used glue) is soft and the seal is ready to come out. You don’t need to perform this step, however it makes removing the old seals MUCH easier:

Using your custom fork seal removal tool (or screw driver) proceed to remove the fork seal, it should pop right out but may require some force:

Works like a charm =)

In some cases there will be a removable seal seat. You’ll want to take this out as well and clean it with the rest of the parts. If it’s rough from rust, etc. try and sand it smooth with high grit sand paper, otherwise it may need to be replaced completely.

Ready for some serous cleaning:

Next take the upper fork tube and remove the springs and rebound stay. In some cases (on honda’s) this can be done by unscrewing the fork cap. However on this Yamaha you simply pop the rubber cap off the top, force down the spring holder and unhook the spring holder stay spring. Be careful, there’s always some spring pressure on this and you don’t want parts flying all over the place:

Now that’s complete we can remove the remaining parts and get ready for cleaning and rebuilding. Once I start the rebuilding process I’ll update this post with more information.

CX500 tachometer noise

Well yesterday on my way out to grab more degreaser for the XS400 project I noticed the tachometer is sounding much like a dying cat. After a quick search of Chopper Charles forum a solution was found. Now I just need to stop by the local hardware store and pick up some graphite.