Cy Welch

I'm not sure that the part numbers would be the same for the 1981 model as for the 1980. If you go to their web site, you put in your model and year and they give access to the parts diagrams. It's easy to get the parts number from there, and as far as I can tell, the only way to order them is from the parts diagram listings. There might be another way, but I haven't seen it. IIRC you said you have the DOHC model which will have different parts than my SOHC model, but being a year newer if anything they should have more parts available not less.

I got mine from bikebandit.com. They have a LOT of parts for vintage yamaha's available.

That's interesting since the name says the opposite. WD stands for Water Displacement and it was designed initially to displace water off of parts. We used to use it in ROTC as one of the final steps in cleaning M1 Garrand rifles (used hot water for part of the cleaning and WD40 to get the water out). As for that, as soon as you start the motor you get oil onto the cylinder walls from the oiling system which replaces the WD40.

And make sure it's on the center stand when you check it. If you fill it to between the lines with it on the side stand it will be way overfilled.

I would still recommend adjusting them with it running if you can at all get it set up to. Then you can actually find the best setting. When the idle is highest that is about where you want it. You might go back just a little in from that point if you want it slightly lean (slightly lean is not really a bad thing at idle) but running gets it best. When it's right it will drop right back to idle when you let off, no hanging at all. The idle hanging high is a prime sign of it being lean.

My experience with exactly the same symptoms was that I was still way lean. I setup so I had gas with the tank lifted enough to get to the idle mix screws and then adjusted them out till highest idle and starting back down and then came back to the highest idle coming down. I did this to both carbs and had to turn the idle speed WAY down in the process as it went from 1200 RPM to almost 4000 just by adjusting the mixture. I ended up about 5 and 5 1/2 turns out on the mix screws, I know that is way out from spec, but what works works. If you haven't replaced the o-rings on the idle mixture screws you probably need to, but try adjusting it first just in case.

If it's anything like mine was, after sitting 13 years (prepped for storage first) the seals in the top end all turned to rubber rocks. I had to replace all the external rubber seals (cam seal, the rocker rod seals etc) to get the hemoraging to stop (it's the only way I can describe it). On mine the seals that had oil against them while stored all seem to still be fine, and I think I still need to replace the valve seals yet, but the major leakage is gone (90% was from the cam oil seal).

That's why I replaced my OEM junky fuse block with an aftermarket one that uses the newer blade fuses. Must better connection and much more reliable.

Leaking vacuum? There are several kits available, and frankly when they work right, I love not having to worry about turning them off and on all the time. When I shut it off fuel flow stops, when I start it fuel runs. I have two of them and one leaks and the other doesn't. Haven't really dug into the one that leaks yet since I have a working one, the other is just a spare.

Make sure you got the idle passages clean when you cleaned the carbs as that will keep it from idling. At that age the o-ring around the idle mix screws may have deteriorated and need replaced, this may be hard to find depending on the carb.

The XS400 doesn't use wasted spark, but only fires at the proper time for each cylinder.

Make sure that the float level is correct. If their too high or too low it won't run well. Also when adjusting the idle mix I found that adjusting it out until the idle speed started to go back down and then leaning back out for max idle speed worked well for me. Mine starts on the first tap of the starting button now and if cold I use full choke for about 30 seconds and half choke for about 2 minutes. No high idle even with the choke on any more (which is used to do always). One thing I found wrong as well was that one float didn't have the float chambers at the same height (apparently I bent it slightly at one point) so I made sure that then were both at the same height and adjusted according to the manual and I was rather surprised at how much better is was. Very careful attention to detail making sure things are correct and it should work fine.

Make sure you have enough slack in the cable. There should be enough to prevent this happening. You should be able to twist the throttle a bit before it starts to open the throttles with the bars in the middle, and if it's right it should prevent your problem. If the cable is too tight it will do as described as the cable tightens when the bars are turned.

Fuse Block. These things are famous for the fuse block going bad. Consider replacing with an aftermarket block if it's chewed up too bad.

Well I found that in is lean and out is rich. I also found that the floats were about 3-4 mm's low so after adjusting them and then adjusting the idle mix it's running really good.

That will be my next project, to work on the lean issue. I got the leak fixed finally by using the recommended sealer (finally found it, and it specifically states it's used for mated machined surfaces as one of it's applications) and making sure that the cam seal was fully seated (found it was not fully seated and I think it was leaking around the edges) and it's looking good now. It's nice to have a dry engine (on the outside) for the first time in a while. Now to replace the tach cable (which is damaged and leaking) as I'm getting a slight leak there, but I knew that and expected that, and it's actually very minor, not wet, just kind of a slightly oily look just below it. I have richened the idle mix a LOT and idle is quite good now, but it's had little to no affect on higher RPM running. I'm pulling the carbs this week sometime and when I do I'm going to raise the fuel level by a couple of mm's and see how that affects things. I guess worse yet is that the 1980's use the bs34-III's and they were intended to not be adjustable. No adjustment on the primary needle etc, so I'm hoping I can accomplish what I need by just raising the gas level slightly rather than having to change jets (I don't really want to go there at this point).

I think we have a confusion of terms. When I say lower, I mean as far as the measurement which is done with the barb upside down so IIRC decreasing that measurement which I am calling lowering actually raises them in operation. I'd say the confusion is all my fault though. I found yesterday that while things seem pretty good at temps at or below about 70 degress ambient, that at around 80 it gets really baulky once off the idle circuit. Loss of power and such. So, cooler air runs good, warmer (hot?) air means not so good. So, lean or rich? The plugs are pretty white when I check them when I get home after getting off the freeway, but with the temp thing I'm not as sure now. I do get the same bit of jumpiness, but around 5-7 k and when it was hot it was trying to bog. So, warmer thinner air means less opening of the vacuum slides right? So less fuel and leaner? Or do I have it backwards? I'm going to try raising the fuel level a bit as see if the problem gets worse or better and go from there I guess.

Ok, so what do you use? I'm still having seapage problems and I'm just about at my wits end. I'm going to try plain old thin brush on gasket sealer this weekend (the next point where I have time to work on it) and see if that helps. Somewhat off topic, my idle seems almost perfect now, but I get just a bit of hesitation between idle and main circuit as a pass the 1/4 throttle point. I'm also pretty sure at this point that I'm a bit lean above idle so I'm thinking about raising the fuel level 1-2 mm (lowering the floats) which of course means I'll have to adjust the idle mix all over again. I just want to get everything working smoothly at the same time and then keep it going for a bit over a year, then I tear it down and go through it.

Properly maintained the drum brakes can work pretty well. Granted not as well as disks, but generally your stuck with what you have unless your willing to do pretty massive modifications (like switching from spokes to alloys etc). I love a somewhat easy way to convert to disk, but I've accepted the fact that I would pretty much need to turn my 400G into an SG to get there.

Additionally on those I have seen, lever straight down is on, forward is reserve and facing the rear is prime. Putting it in prime will indeed tend to make gas run out the carbs if there is ANY problem with the needle valves. I would suggest that if there is no problem with the lever straight down there is no reason to replace the petcock. Actually I find that if they are working properly it's much simpler since you don't have to remember to turn the fuel on and off each time, since starting the engine turns it on and stopping it turns it off. My 27 year old petcock works just fine, while the one I got on a replacement tank doesn't (but then I haven't really spent any time trying to fix it either).

Well I tried again and followed the directions on the tube and it seems to have worked so far. I'll see how it goes over the next few days but it seems to be properly sealed without seeming to have affected the valve lash or other aspects. I will be keeping an eye on it of course as I'm a bit nervous about it.

Both carb holders should have a vaccum barb on them, one should already be plugged and the other should be hooked to the petcock, just cap that one when changing the petcock and your good.

Ok, I attempted the job today and got the new seal installed and that leak seems fixed but I'm having a real problem. The manual calls for liguid gasket for reassembly, which I can't seem to find. I tried RTV gasket maker and it's not sealing (I've got leaks all over the place). Reading the instructions on the package for the RTV gasket maker I think I did it wrong so I'm going to try again tomorrow and follow the instructions (run the bead, place the part, finger tighten until the material starts to press out and then stop and wait 1 hour before tightening and torquing the bolts.) I'm hoping this works properly since seeing how this is put together I'm pretty sure that the thickness needs to be pretty close to zero to give the right tolerances. My other option may be to try a product that is similar to what I've been trying but that says no wait is required, just apply, assemble and tighten and use right away. Other than that, is there something else to look out for?

Ok, this weekend I finally removed the blind plugs from my idle mix screws on my 80 xs400G and before doing anything else at all I removed the mix screws. Interestingly, they are NOT pointed be have flat tips!!! Exactly the same length and appear machined this way, and since the unit is sealed (and being the second owner and knowing the first owner didn't open the carbs EVER) I'm pretty sure nobody screwed them in and damaged them. So, I sprayed carb cleaner into the openings and then blew compressed air through them to clear them out. Then I put the screws back in and took them down carefully (didn't force them at all) then turned them out 2 1/2 turns (no specs for 1980 so I used the 1979 specs) and it does seem better if its a bit warmer out, but if it cold boy it idles bad till the weather warms up. So here is the question, it's a lot better than it used to be (at least it will idle nicely and doesn't backfire like crazy when decelerating anymore) but to make it richer do I turn it in, or do I turn it out? I seem to find conflicting information on this thing, most sites say that a mix screw in this position adjusts amount of fuel and air mix screws are adjusted from the back of the carbs but I have recall having seen here I believe that the bs34's are mixing air and opening them leans the mix. I'm not looking to get real precise quite yet, just trying to take small jumps in the right direction as I know it's still a bit lean so I want to richen it a bit and see how it does. Next payday I'lll probably spring for a colour plug so I can get it precise, but for now it would be nice to get it in the ballpark until then. Thanks in advance for any help you can give.

I'm hoping someone can help. I have an oil leak from what appears to be the seal on the camshaft behind the electronic ignition module on the head on my 1980 XS400G. I'm hoping there is a way to replace this seal without breaking down the whole top end as this is the only leaking seal on the engine and if I can solve this leak I should expect to easily be able to get at least another year or two out of the engine before I take it out of service and refresh it. BTW this is the original engine with 45000 miles on the clock, compression still in spec and no apparent oil burning, just seeping (heaving seeping) from the cover over the igniter module. It's using about 1/2 cup of oil every 250 miles or so, all of it running down the side of the engine. Can this be done without breaking it down? Can I take the ignition module from the end of the camshaft and get to the seal to replace it without pulling the head (and can I get this seal without a complete seal kit)? Thanks in advance for any help you can give.