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Get the bike's wiring diagram and identify the relay control wire, cut this not the pump feed.

If you only use the kick starter yes you can fit a much smaller battery. I wouldn't fit a battery less then 5 amp hours with the standard regulator

Hehehehe someone got out of bed the wrong side Its well documented the XS 400 has marginal charging. I've not had good results rewinding these generators to give more power - they have an odd fixed field winding which limits their potential . Expensive too.

Lets think about this........ 36 watts at 13.8 volts = 2.6 amps. 55 watts at 13.8 volts = 3.9 amps. So your sat nav IS NOT 'bugger all' power in terms of the system's capibility, its in fact drawing more then half what the head lamp does. If it's internal battery is flat I'd bet it draws a damn site more, I wouldn'be surprised if it took 2 amps to charge its battery - so it would be like adding a bigger second headlamp! Most of the wiring on the bike is 1mm squared area with a 11 amp rating. Lets think about that, headlamp 4 amps, instrument lights, pilot light and rear lights lets say a total of 25 watts, so 1.8 amps. So your lighting alone is drawing nearly 8 amps. Admittedly this won't all be felt on one single 1mm squared wire. Your ignition draws 2 amps and you have to consider battery charging which varies, but could be as high as 4 amps (normally less then .5 amp) So engine running lights on theres 8 amps, 2.6 amps is approx a 33% increase in load. If you replaced the tail lamp, pilot light and instrument lights with LEDs you'd free up something like 1.25 amps, so it is worth doing. If you have a twin bulb tail light, LEDs are bright enought to just use one, freeing up more power (the XS650's charging system is even more marginal then the XS400. I have fitted LEDs in all lamps bar the headlamp and now there is never an issue with battery charging or bulbs blowing)

...Assuming your multimeter is calibrated. i wouldn't fret over slightly off readings with a cheap one. If its a wet battery, it still has its electrolyte in it? A good check to see if the charging is working is does the headlamp brighten up when you rev the engine off idle. Nothing like winter to kill off a battery, have you used an optimate on it?

Sat navs are fairly power hungry, there's a receiver and processor running all the time. If it were my bike I'd feed a relay directly off the battery, via a fuse (this will protect the circuit). The output of the relay I'd supply my accessory socket from. On most Yamahas the brown wire in the loom (do not confuse with the brown on the left indicators) is live only when the ignition is on. I would use this to control the relay IE Ignition on = socket on. Ignition off socket dead. Feeding directly off the battery puts no extra load on the wires in the loom plus you avoid loading the contacts in the ignition switch. But thats just the way I do it if you bought your bike to my workshop. If you want a simple lash up connect the socket direct to the brown feed. You will be running the brown wire very close to its maximum rating, plus feeding through the contacts in the ignition switch. You'll get higher losses this way, but it will work. Switching to LEDs is a good idea.

A good thorough ignoring works wonders in the short term

I'd say that was a very reasonable price for a regulator. As to if he should sell the bike I can't answer. If you were in the UK I'd offer to test the TCI to see if it was faulty (I have a proper test rig that will run most ignitions on the bench)

it could do if you have a TCI. If the voltage dips below the operating thrashold of the igintion unit it may cause the timing to drift off, or the unit to stop working althougher.

For automotoive parts, if you are going to subject them to more use in winter, Id get the parts blast cleaned, this will remove all the corrosion thats there.Yes you can do it with abrasives but it takes forever and on diffeicult shapes you never get rid of all the corrosion totally. Blasting on the other hand will. I very much doubt you'll find anodising kits on the commercial market, but you will find chromate based etch primer in aerosols (look on aviation sites). This stuff reacts with moisture and releases chemicals on the metal's surface to kill any further corrosion. Then finish with normal top coat. This is no good if you want to use clear laquer, unless you like militray looking yellow or green as a finish.

Add on alarm - bin it. They cause nothing but problems.

i doubt you'll find an odd ball wattage like that these days, unless you live in a market where that is the the legal requirement. try this guy... http://www.norbsa02.freeuk.com/whatsnew.htm I ran a XS400 on 55/60 with no problem.

Same as rebuilding any brush type motor, google it!

Disconnect the brushes (reomove the holder assy to be sure nothing is connected across the slip rings)and measure the resistance between the 2 slip rings on the rotor. anything less then 4 ohms or an open circuit and the field windings have failed. very common on the XS, more so then regulator/rectifier failure.

First of all you need to work out what type of wire is used in the loom, there are two standards; traditional and modern thin wall. This will effect what wire you need. Second don't confuse wire diamenter with cross sectional area. wire is identified by the area of the conductor. A wire with a 1mm squared area is too big to fit in a 1mm dia hole. If you measure with calipers you will find the wire diameter. Most standard wire in the loom has a 1mm squared area, main feeds will be bigger. Stick to what ever standard is used on that loom. I know the thin wall looks too thin to most people, but its the better option.

Thats odd, drilling the discs is a popular mod that works well on these bikes. Just don't drill too close to the edge! See XS650 brake mods (google it) as the 650 had a very similiar set up. Most modern discs are drilled and I never heard of discs being heat treated (apart from after each hard stop from high speed)or cast with holes! Dumping the rubber hose will help greatly!

so long as its secure, works without affecting other lights it will pass. You need a reflector if it hasn't got one in the lens.

OK if that diode is connected to the kill switch is there to aid the kill function.

Thank you for your patience 1 3 4 2 sound right for an in line 4. Coils are normally paired up - odds and evens. Loquacious intro btw.

I have to buy these in boxes of 100 as the cost of one is tiny. But the ones i use have running voltages too high for what is needed here. They need to be matched to application. These can drift off spec so i'd change it to be sure. This type of diode is a little more complicated in its operation then a simple onewway valve.

I suspect you still will have a fault as that diode is in the AC circuit for the lights, not the battery side. That is the voltage regulator shown next the the generator. Are there any numbers on the diode?

Right that resistor/diode with the green bands near the brake switch that cant be identified...... ......its what is known as an avalanche diode. Google it, but trust me thats what it is. It gives a very stable break down at a controlled voltage like a zener, so I'm guessing thats what is used to regulate the voltage. I think if you look at the wiring diagram there is one generator coil for lighting and one for running the battery and other lights? If thats right there won't be any control on the power for the headlamp, it'll be AC as well. Can you post the wiring diagram...I'll have a proper look at it?

That set up would be 1000% better if he ditched the points. He's got all the hard stuff sorted!

13 volts is about right, direct off the generator, don't forget you'll lose a fair bit at the rectifier then the voltage regalutor will control to a lower level. If that was the level measured AFTER the rectifier and regulator then you do have a fault.

I wouldn't bother. I used to sell these kits years ago. I binned them as the warranty issues where too much to deal with and I got fed up with having to take the systems off customers bike and putting the orginal points back on. The 2 stroke kits were OK, but the 4 stroke kits were terrible. The had a nsaty plastic rotor that caused some of the trouble.