gmkieran

Welcome to the forum and the joy that is re-building an XS!!! I just finished (mostly) bringing a '79 back to life that had sat the past 15 years. I got nothing until I went back into the carbs for the 6th time and took them *completely* apart. Turns out the idle jet passages (not the jets themselves) and the atomizers in the main jet passage (brass tubes into which the main jet threads - didn't even know there were removable to begin with) were both clogged. If you can, tear the carbs all the way down and soak them. If you can't do that, at least pull them as far down as you can and use pipe cleaners to get to the passages. Don't forget to get the choke passages, while you're in it. make sure that the jets attached to your floats move freely, too. Take a look at the service manuals stickied at the top if this thread, if you don't already have one for your bike; they're invaluable! To the electronic ignition question, not sure if you mean electric start (check for a push-button control on the right-hand bar with a wire running to a cover directly below the carbs) or electronic ignition timing (check the cover on the top left of the cylinder heads - if you can remove it, you have points, not electronic advance ignition). My '79 has both, I would expect your '80 to, also. Rather than putting gas directly into the plug wells, pull the air boxes (leave 'em off, for now) and blow a little starter fluid into the carb air passages (both sides) while holding the throttle open. Then try to kick it. If it tries to fire at all, that indicates that your coils are good, at least. BTW, if the carb rubbers are cracked on the outside, they're probably not going to seal properly (no matter what the inside looks like) and will need to be replaced sooner rather than later. best of luck and have fun!

Google turned up these guys for me: http://www.650central.com/carb_oem.htm

Guess that's what I get for cheating. The local boneyard has given up on cables, because they never got any salable ones. So, anyone got a line on stock minus 6-8 inch cables for an XS400? Or know of another bike that had a 36" clutch cable or 41.5" brake cable (yeah, I had those reversed above) that might work on the XS?

So, I'm cheating. I've measured and marked the lengths on my current (too-long) cables and I'm taking them to my local boneyard to see if they have anything the right size. If I can't find anything I'll look into having custom cables made at motionpro or something. For anyone who might be interested, the brake cable was 92 cm / 36" (ferrule to ferrule) and the clutch was 105 cm / 41.5" (ferrule to ferrule) for the superbike bars.

It Fits! IT FITS!!! far too much hammering and sanding and checking and more hammering and more sanding and some painting later, the bloody tank FINALLY seats correctly (and the seat has been modified to fit behind it until I can get a new one). Photo evidence below. what I had to do to the frame the results

Ok, so I finally got around to switching out the bars in my cafe project. The new bars look great (will post pix once I get things back together), but nearly all of my cables are waaaay too long. Anyone happen to know the appropriate lengths for clutch cable, front brake cable, speedo cable and possibly throttle on a 1979 XS400_2F with superbike bars in place of the stock buckhunters? The current clutch cable (may or may not be stock) is 51.5", current throttle is 31.5". Haven't measured the brake or speedo, yet. Any help would be greatly appreciated as I'd like to avoid the trial and error method on this one!

looked at it today, in fact. may or may not work (there's a *lot* of difference between those two tanks, in fact) - have to check the measurements if I ever get the 750 tank installed. On that note, any chance you could give more detail on *how* you modified your frame to fit the petcocks with the 750 tank and/or attach a photo of the modded area? I spent another 4 hours tonight trying to find some combination of frame mod and petcock re-configuration that wouldn't put one or the other of the outlets dead center of the frame uprights; complete failure. Out of curiosity, did you go with the 750 petcocks or something else? I'm thinking I may get a second 400 petcock and just run 2 of those - with just a *tiny* bit more mod I can make them work, but I'd rather have the 750 petcocks if I could just get them to clear the frame (esp after the time and effort that went into obtaining the bloody things!). Thanks!

I can't, either, but there appears to be no significant wear on the guide. If I can track one down, I'll replace it, just to see what that does (can't hurt and it's cheaper and easier than anything else I can do).

The parts finder lists that as a chain guide rather than a tensioner. I was hoping, when I first got into the case, that it was actually a tensioner, but there's no adjustment to it. It's just a piece of hardened rubber that lays along a section of the case and keeps the chain from making a racket. I was referring to the idler gear like the 850 has (part 1 in the image) when I said tensioner (sorry if I used the wrong term!).

bznchris, what did you do seat-wise when you changed over to the 750/850 tank? I'm trying for a cafe look and I'm almost done with the frame mods to get the tank in place, but it's either going to end up sitting lower than I want it to or interfering significantly with the stock seat. Trying to figure out a) what I can do with the stock seat so I can ride until I can track down a cafe-style seat that will properly fit with the tank wherever it finally ends up. Thanks!

Chain's brand new - I replaced the old one thinking that might be the problem, but the new chain (which looked and measured exactly the same as the old) still slips past the main sprocket teeth without grabbing. Initially it had more tension than the old chain (1/2" of play v 1.25"), but after the first run at starting the bike the new chain was back to 1.25" of play and there's no bloody tensioner in '80 400. Neither sprocket nor the chain guide appear significantly worn, so I was hoping the added diameter of a couple extra teeth would tighten things up enough to get the chain to grab.

I posted a diagram of the BS34 Mikuni's that I found very helpful in figuring mine out - it's in the stickied Links post at the top of this thread.

Unfortunately, I'm looking for the starter sprocket, not the front drive sprocket. Sorry if I wasn't clear on that. Thanks, though!

Finally got the new tank! It's better even than I'd hoped (at least in terms of looks). think I've figured out how I'm going to do the mounts - no welding, but it will involve grinding the old catchers off the frame and some drilling. Has anyone else mounted a '78 XS750E tank on a '79 XS400_2F frame? I'm running into clearance issues with getting the rear of the tank to fit down onto the frame and wondering if any one has suggestions. Although it occurs to me I may want the tank to set more level than the old teardrop did, so suggestions on how to mount the tank with the back end raised would also be welcome! getting petcocks and a cap to go with it - should have those soon. Something else that's beginning to bug me - the electric start won't work. I've pulled the cover and replaced the chain. both sprockets appear to be in good condition (teeth aren't worn or broken) and I've verified that the clutch engages correctly, but the chain just spins past the teeth on the main sprocket and doesn't turn the engine over. Kick starts fine (when the carbs aren't clogged with rust from the old tank), so I know there's no issue there. I've been trying to track down a starter-side sprocket with more than the stock 13 teeth, but haven't had any luck. Anyone else ever encountered this? Or have a source for 15-17 tooth starter sprockets that will fit the XS400?

According to the OEM part finder here: http://www.stadiumyamaha.com/pages/parts/viewbybrand/parts.aspx they are not the same part. The 400 takes damper 256-23434-01-00 while the 650 needs 1T4-23434-00-00. That said, here's an ebay listing for NOS dampers for the 400: 160357582033 (I know, the listing says they're for the 650, but the part number is clearly the 400 #). Good luck!