Speedshop

a 120 is too big, 110 is a little big, but acceptable. The wider the tyre the slower it makes the steering. BT45s work really well on 70's Yams, they calmed my XS650 right down.

You might be lucky and find the pin outs in the wiring diagram for the bike.

google it, 87,000 results for mikuni bs32. Take your pick!

I be extremely surprised if a duplex chain chain was worn in such a small mileage. It should out live the rest of the bike! I'd do some more research first. You will get a small amount of slack turning the engine backwards, thats normal, you don't want the chain bowstring tight! If the tensioner is backing off I'd say it was faulty. It would have to be VERY lose to skip the sprockets, I had a tensioner break up on an XS400 and even with a very worn chain and no tensioner it didn't skip the sprockets. Made a hell of a din though.

Why not discount some of the things that don't cost anything to look at first? EG lose wires/connections, before jumping in with something that's expensive to replace!

I get over run with them sometimes! I have loads of engines at the moment, I had to break on as I was running out of space!

If you know someone with a TIG welder you can buy pre-bent sections of exhaust and get them cut and welded to suit. If not its down to the breakers for a good session of trial and error!

I'd set them so they just about remain in the same position when you let go, only just though. Any slight nudge should cause the swing arm to drop down.

What are we talking about here the rudder on your boat? Swing arm? Suspension arm on a car? With bronze bushes they are only going to get worse with age, so I set them up a little on the tight side to start with. Not too tight though, I've never measured with a spring balance, just checked to see if it feels right.

What are we talking about here the rudder on your boat? Swing arm? Suspension arm on a car? With bronze bushes they are only going to get worse with age, so I set them up a little on the tight side to start with. Not too tight though, I've never measured with a spring balance, just checked to see if it feels right.

Have you kinked the fuel pipe when you put the tank back on?

If its anything like the SR500 it will be TIGHT, with a very capital T. You need the correct puller (i think its the 20mmx1mm thread) and make sure you get the puller screwed right in. Then an air impact driver on the center nut to remove the flywheel. Over the years I've come across this problem so many times I bought my own compressor and impact driver.

When something isn't working right forcing it is rarely the answer! (nor is pretending that a changing the oil is the mechanical equivilent to a trip to Loudes)

It depends entirely on the rest of the engine set up. I had a xs400 that I fitted a very open pipe to and that made it run very rich. Rule of thumb increase the main jet size until you get a rich misfire, then come down 2 sizes.

Not all the mods have to be published on the VOSA web site, if its a mod to stop a later failure but doesn't have a safety issue they won't publish it. And yes legally you might be correct, but when you come to sell the bike no amount of stating that legally you are in the right will put a buyer's mind at ease about a 'dodgy' first service!

Diodes are simple to check, capacitors less so. I have a test rig that will run the box off the engine so its easy for me to check if the parts I replaced have fixed the problem

I have a test rig that will run AC cdi boxes. I built it myself and it simulates the generator, altering the voltage and frequency as the engine would as it runs up and down the revs. there's a few other features I included to test other functions as well

I would STRONGLY advise you to have the service done. You're thinking that it is straight forward is correct, servicing a bike is not rocket science. BUT Yamaha could have service bulletins and modifactions that need to be incorporated and specific items to be looked at to ensure your personal safety and avoid you having mechanical problems in the future. You may not be informed of these, they will just be carried as part of the service(I used to work in Yamaha dealership) Besides this a bike with a missing first service will be worth significantly less when you sell it or if you have a warranity claim the first service not being carried out will be used as a reason for the claim being refused. If I were a dealer I wouldn't entertain buying back such a bike at part ex.

If you can get the number from the old transistor it is usaully possible to find a data sheet for it, then you can choose a commonly available modern replacement. I've done many over the years, just because they use a heavily rated transistor doesn't mean its required. I've seen it wher they have used transistors rated at 5 amps, then changed a minor detail for a newer model but then used a transistor rated at 0.5 amp for what is essentially the same system. They play lots of tricks to stop ignition boxes being universal. With the pulse coil input there are 3 basic designs of filter stage, none offers any real advantage over another, but one system will not be compatable with another so have to be accurately matched to the pulse coils. So they will swap and change the filter stage to prevent boxes from similiar models being used as replacements for other machines. I'm talking about older analogue set ups - this isn't the case for new digital systems where programming is specific to an engine. 9 times out of 10 its a transistor, but a resistor can catch you out too

true, its often a simpler fault; spark plug, wiring or a generator coil, i was assuming these had been tested? But i can test the cdi box if needed as i have a specialised test rig that will run the box off bike. Generally they can't be repaired, unless you can open the case and see the circuit inside. Most of that type of cdi was sealed with epoxy compound meaning you can't get at the circuit board.

Copper or solid plug wires are the most reliable, an NGK resistor cap will be fine. It is maybe an odd thought, but the resistor actually makes the engine run better. Why? The voltage has to build up more before it can jump across the resistance, giving a much cleaner, higher voltage spark. You'd think it would be the other way round, but will high voltages and high resistance odd things happen! Without the resitor the spark with be more spidery and lower voltage, although you'd need test gear to see the difference.

As an aircraft engineer I'll tell you what we use PR1005L for.....its to protect the main fuel tank sealant while it cures. Its painted on with a brush over the PRC sealant so we can get fuel back in the tanks quicker. I'm not sure I'd trust it for the sort of repair you have in mind, its too thin for a start. I'm guessing all the holes are in the bottom? I'd use something called deox-c (google it) to remove all the internal rust then depending on how bad it is weld or braze the bottom of the tank up. If you want extra piece of mind Pr1005l would protect the repairs inside the tank for a very long time. And yes avoid the epoxy sealants, unless you enjoy picking bits of it out of the carbs.

No such thing as cheap! i may be able to help with the cdi box. I build them for some of the big single 4 stroke yamahas, there's not much difference to the 2 stroke machines in terms of cdi ignition systems.

I can't imagine XS400 carbs being expensive, they'd come up cheap at either a breaker's or on ebay. But if the diaphragms have pin holes in you need new ones my friend!You could replace them with a pair of mikuni VM carbs, but by the time you bought the carbs and all the bits you need you'd be well over the cost of a replacement XS400 carb assy. The 400 had a weird rotating field magnet and stationary current windings similiar to the 650. Unlike the XS650, which has slip rings to take the power to the rotating field coils, the 400 uses mutual induction to a slotted piece of metal, very odd. I seem to remember issues with the wiring around the gear selector - worth having a good look at the wiring and check with a multimeter before lashing out the cash. The lack of charging MAYBE be adding to the running problems, I remember one of my old XS400s running very rough when the regulator gave up on it. Do you have a solid state rectifier/regular or the seperate rectifier and vibrating contact regulator?

Yup that's my XS650. I don't have a picture of the running SR500 with me, but you can see one of the SR500's I'm building up here.... http://www.sr500forum.com/forum/viewtopic.php?f=15&t=44 I'll dig out some more pictures when I get home I'll be looking for an American import XS650 when the SR500 tracker is done, I've got a 750 bigbore kit and a desire to build a new frame around an XS lump