Sonic’s Workshop: Yamaha XS400

For those of you who still remember OMG, the following may seem a tad familiar. It was originally published back in 1996, but since it’s never been posted on CMG (hell, CMG wasn’t even around then – which accounts for the black & white pictures), and Sonic is taking his sweet time with a new piece, what the hell. Tell you what, if you don’t like it we’ll give you your money back!

The Yamaha XS400 makes a good starter bike that is very user friendly, with the exception of a crap starter gear design, common to many Yamaha’s of that era, e.g. the XS 650, and the early Virago 920 and 1000 models. Other than that, the motor’s a reliable unit.

The bike I picked up was in fair shape cosmetically, with few miles on the dials, a complete motor still in the frame, and a brand new two into one chrome header. Always a bonus.

Anyway, here’s the usual breakdown:

Engine: Complete unit with a compression of 140 psi on #1 and 146 psi on #2. A minor oil leak from the shifter shaft seal and drain bolt was visible. With the unit not running it would be difficult to accurately access the transmission. Also, we’ll assume for now that unless the starter gear has been replaced, it’ll be crap.

Suspension: Both fronts and rears were in good shape. The steering head bearings had been replaced at some time and as a result the nut that secures the upper clamp to the lower one had the b’geses torqued out of it. Fortunately the bearings and races survived the ‘Armstrong technique’ of installation.

Wheels and Tires: Both rims (mag style) were in good shape along with their respective bearings. The back tire was passable but the severely cracked ‘Chen Shin’ front tire wasn’t even safe for the bike to be parked on – New front tire required!

Chains and Sprockets: This was a bit dry and loose but still had plenty of life in it. Both sprockets were in good shape.

Brakes: Both front and rears were down to about half their life but still quite usable.

Cosmetics: The overall appearance of the bike was good, although the seat was pretty rough and should really be replaced. The paint was still original on the tank and both side covers.

On any motorcycle, the engine is the machines heart, so it’s a good place to begin. There’s no point in buying a new tire and having it installed, only to find out the motor needs a rebuild, thereby possibly making the project unfeasible.

I picked up a new Yuasa battery, charged it S-L-O-W-L-Y (very important) and installed it in the bike. I checked the oil level, which was a bit high, but nothing to worry about. Besides, my neighbour said he would do the oil change later himself. I then set the valve clearances, the points (ignition timing), and finished with two new spark plugs. Fortunately, this bike comes with a kick starter, as well as the electric start, and so allowed me to slowly hand crank the engine (with the ignition off) to circulate the oil prior to starting.

On a bike that’s sat for any real length of time it’s a good idea to whip the carbs off and have a look inside for any varnishing left from old gas. This varnish can easily clog the jets, stick the floats, and completely plug up the choke circuit. My local dealer recommended Yamaha combustion chamber cleaner for all the non rubber parts of the carburetor. It’s about $8.00 a can and does a fantastic job in a very short time. The carbs on an XS400 are a breeze to remove and install, but as always, I recommend you have a manual before tackling any job.

With the carbs removed I discovered that the rubber intake boots, that the carbs fit into on the engine side, had severe cracking on the inside of each boot. These cracks would have made starting difficult and smooth running impossible to achieve. Yamaha’s $37.00 price tag for one of these items provoked me to look to the used part dealers for a cheaper alternative. However, beware when buying items like these used! Inspect them closely before buying as they may also be on their way out! As it turns out, I found a parts bike for sale while cruising the Buy & Sell newspaper. $50.00 for a whole bike, or almost whole bike, that also had good inlet rubbers and so was well worth it.

Sonic with ‘bitsa’ XS

With the new inlets on and the carbs back in, I fired up the bike. It started first shot, idled and revved out smoothly, and emitted a nice exhaust note from that new two into one header pipe. The rest of the bike went without incident. The owner picked up a used tire, with good tread life still left, and it was installed without undue stress. There were a few lights out, but they were simply blown bulbs. The charging system also checked out, which can be a weak spot on some of the early Yamaha’s. Even the transmission checked out fine on the test ride – finally, a simple one! (No, this is not what the readers want. We need pain, suffering, death? – Editor ‘arris)

The owner came round and drove it off a happy camper. Of course, he called two days later to say it was running rough and difficult to start. This is the Sonic article after all – something always has to go wrong!

He brought it back and so I whipped the plugs out to find them covered in black soot, too rich! I checked the air filters, the carb set up (including the stock jet size) and removed and inspected the exhaust for blockages. Everything checked out, so why wasn’t it running then? I decided to try it without the air box and filter, and it suddenly ran fine, albeit a bit lean now. With the bike still running I reinstalled the air box followed by the filter and the bike continued to purr along.

It wasn’t until I reconnected the crankcase breather hose to the air box that the motor began to stumble and quickly die. I removed the hose and restarted the bike, it ran fine again. What’s the deal with the hose? I put my thumb over the end, man there’s a lot of pressure coming out of that thing! Stop the bike, let it cool and re-check the oil level. It was high, but now that it was warm it looked like dirty varsol and reeked of fuel. I grabbed a pan and drained the oil. Seven liters of gasoline contaminated oil filled the pan – Three liters of oil and four liters of gas!

When I had originally checked the oil the bike hadn’t been run, so all I can think of is that the gas was probably already in there but it must have never really mixed with the oil. Gas on its own would be difficult to see on the XS400’s silver dip stick. It’s a good point to remember that the carbs on an XS400 do not have an over flow pipe, so if the floats stick the gas will dribble straight into the engine.

All in, the bike was still a good deal.

The cost of an XS400 ranges from $50.00, for a good parts bike, to about $1000.00 for a good running example. There are still a few good deals out there, just be careful and leave the rose colored glasses at home!

Sonic