paultsmith

Thanks, I'll recheck all of the wires. It is only intermiten, as I have only been shocked once, and was holding onto the HT wires with out a problem. Must be a fault somewhere. I think this may be related to the problem I was having before, when sometimes I would here a puff sound, when I turned on the ignition, I think the coil was discharging or send a high voltage to the spark plug.

Hello, Well yesterday I was running low on gas, so as I was driving I reached down and turn the petcock from On to Reserve. But just as I finished doing this I got a huge electrical shock. I am now trying to find out what could cause this. Any thoughts? I might have touched the pickup coil wire when I was turning the petcock, or maybe the spark plug wires. The spark plug wires are brand new and have new plug caps on them, so I didn't think this would be the problem, but the shock was very strong. Is the pickup coil on top of the cylinder outputing a high voltage too? Any thoughts would be much appreciated.

Is there a way to know if I need to rebuild my master cylinder? I can squeeze the lever and it feels fine and is moving the piston/

Thanks, I haven't rebuilt the master cylinder. I just thought everything was fine since it wasnt leaking, but perhaps the internal seals are not great. Perhaps that is the way to go, but for the price of the rebuild kit I think I might just buy the entire cylinder, $20 for the kit and $70 for the entire control. Besides my reservoir diaphragm is on its way out and the metal retainer is starting to rust. Should I be concerned at all with the caliper piston, there was some slight rust on the outside portion that makes contact with the pads. I cleaned it up and it seems to be fine, but woulld this hinder performance? I also have a rear drum brake. I replaced the pads, however it is very poor also at braking, perhaps just how it is or should I scuff up the drum with some sandpaper for improvements.

I just buttoned up my XS400, turning it into a cafe racer. I am a little concerned about the stopping power. It doesn't come close to stopping on a dime, and I was wondering what componenet is most likely responsible for this. I can really pull on the brake lever and it won't lock up, perhaps I have ABS I am sure I have the air bleeded from the system. I also put it in new brake pads and replaced the seals in the caliper What should I replace to get some more stopping power, brake lines, rotors, piston, cylinder reservoir? I was thinking it may be my brake line, as it is the original and after placing some lower bars I need to snake the line around quite a bit.

I am having an intermittent noise sometimes when I switch the ignition of my bike on. It is an 81 XS400. The noise sounds like a large puff or release of air. It only happens sometimes and occurs about a second or too after I turn the key to run. It happens before I start the bike. It also seems to happen when the bike has been sitting and moved around without turning it or starting it for hours. Any thoughts on what could be causing this? I thought it may be the battery breather venting or perhaps the engine breather releasing some pressure, but am not sure why it would happen all of a sudden once it gets the 12V of power. May also be the carb breather vent or gas tank venting???? It happens every once and a while and I cant seem to pinpoint the problem as it happens pretty quick Thanks

thanks, going to use my 5kohm new caps

I am replacing the spark plug caps and high tension wires on my XS bike. The service data sheet says that spark plug cap should have a resistance of 10kOhm resistance however the new caps I bought have a resistance of 5Kohm and I am having a problem finding the 10kohm caps. Any one know if there will be a problem using the 5kOhm resistance caps? The bike has CDI ignition. There was not a problem with the old caps and whe I measured them they were at about 6kohm.

got it, took out main jet and tapped it out

How do I remove the needle jet on a Mikuni 34 carb? I want to take it out of my 81xs400 and give it a good cleaning, but they both seem really stuck in there.

Is there a way to open the tachometer and speedometer gauges on an XS? I have a spiderweb on the inside and would like to crack it open to clean out the web. I would also like to paint the metal ring around the glass, without having to tape everything off. It looks like there is a metal ring crimped around the plastic to hold the glass on these gauges, but was wondering if there is an easy way to open it up. Thanks

Hello, I have an 1981 XS400. The exhaust headers on the bike are rusted up quite nicely and I have the presence of some RTV where I joined the slipon pipe to the exhaust header. I was thinking about wrapping the header with exhaust header wrap to conceal these uglies but was wondering if it is a bad idea. AS the bike is air cooled, I was wondering if using exhaust header wrap if it would prevent proper cooling, and was wonderig if this would cause my exhaust valves to get too hot and eventually end up burning. Any thoughts?

If you have the transistorized ignition you can check the resistance of the pick up coils resistance. It should be about 700 +-150 Ohms

To check Ignition Coil Measure Ohms Primary coil resistance 4.0 ohms, red/white & Orange Wires Secondary coil 8.6-9.5KOhms orange and spark plug lead

Thanks for your help everyone. I did a bunch more compression tests and each cylinder was giving me the same pressure +-10psi. I also checked the valve clearance and adjusted them. One cylinder was very loose and the other very tight. I reasembled everything and was still having the same problem! Checked compression again and it was good again, so I decided to take apart the carbs. I cleaned the carbs again and put them back on the bike. I will probably need to do some synchrnoization soon. One slide comes down much faster and not as smooth as the other. I also took out the mixture screws and noted that one of the small orings had caught on the spring, so it was probably not seating correctly. I put everything back on the bike and still not much of a change. I left the bike idle for many minutes and then held it at 4-5K rpm. The bad cylinder was sputtering and oil/mositure or gas was visible all over the inside of the left exhaust pipe. It started backfiring a bit and some white smoke was coming out. I just kept it idling at 5k and after a while it seemed to clean itself up. It seems to be running fine now. The bike had been sitting for a number of years and I had put in some oil in the spark plug holes, before along with some carb cleaner into the carbs too. Perhaps there was just a bunch of gunk and buildup in that cylinder that was giving me the trouble. Currently the bike is at the dealer getting safety inspected and new tires, but I drove it for about 20mins today and it sounded good, and there was a lot of heat from the bad cylinder.

So, I followed the advice and got a compression tester. I hooked it up on the right (good) cylinder and got 150psi after a few cranks. I then hooked it up to the cylinder that was giving me trouble, I ended up getting 150 psi in this cylinder too. However I noted that it took many more cranks to get this pressure as compared to the numer it took on the right cylinder. (Perhaps the battery was just running lower on the second cylinder test??) On the bad cylinder I got it up to 150psi and it held that pressure for 8 minutes with no leaks, until I released the pressure. So it looks like I may be having a carb issue now? Also, when I first did the test on the bad cylinder, it would only go up to snd hold at 120psi, but I noticed when I cranked the started, air was leaking from the spark plug hole. I hadn't screwed the tester in tight enough on this cylinder. Perhaps I had not screwed in the spark plug with enough torque?

I am fixing up an 81 XS400 that has been sitting for about 15 years. I have cleaned the carbs and replaced the exhaust and have got the bike to idol. I have also just took the bike out for a spin for a few miles. I have noticed that the plug on the right side looks great, however the plug on the left cylinder is almost completely covered in black soot. Today I replaced the carb boots and when I started it back up I noticed the the right muffler was noticeably louder and pushing out quite a bit more air pressure than the left muffler. I revved the bike up to 5K and held it ther for a few minutes, white smoke was coming from the left cylinder and this cylinder backfired a few times too, however after a bit the smoke seemed to be reduced. When I examined the spark plug again, I had one good and one bad. The right cylinder and exhaust pipe was also much hotter than the left one. I thought it might be a weak spark, but I checked the resistance on the windings and they were good on both sides, I also swaped the leads and spark plugs from each cylinder, but the problem seems to persist. I cleaned the spark plugs and I started up the bike and let it run for jus a few seconds, removed the plugs and the plug on the left cylinder was slightly wet. It was clear and seemed to have some gas on it, but could this be oil? I have not had a compression test done. I was wondering if my problem could be an idle mixture screw problem. I am hoping it is not a valve problem, as I will not be looking forward to taking the cylinder head off and cleaning the valves and ports or replacing the piston rings. Is there any problem with operating the bike with one cylinder running and producing more power than the other? Again the bike has been sitting for 15years, is there a chance that if I just add some intake cleaner to the tank and ride the bike that this problem will eliminate itself? Thanks for your help.

you can try taking the ignition key apart. On mine, when I popped off the bottom cover of the assembly it was badly corroded and good contact wasnt being made when the key would turn. I eliminated this for testing and connected all 3 wires leading from the main key switch together, you may want to try this and see if that fixes the problem. btw my bike was an xs400

mikesxs.net sells boots for both 38s and 34s. also cross reference your bike with the part numbers on the xs650 to see if they use the same parts. Yamaha part numbers can be found here http://www.yamaha-motor.com/sport/myyamaha.../starthere.aspx

Thanks to all, for the record, the bolt was the large 17mm bolt on the bottom that extended the farthest towards the ground. It was stuck on like a MF however after taking a torch to it for several minutes I was able to finally get it loose. Thanks to anyone whom read this post.

Ok so I have a 1981 XS400 and am going to change the oil for the first time. (In the process of rebuilding it) On the bottom of the crankshaft underneath the oil filter housing, there are 2 bolts, but I am not sure which one is for the oil drain plug. There is one bolt that hangs down quite a bit lower than the other. I tried looking at the parts diagram however the iso view is not quite clear. By the way is there also appears to be another similar bolt on the left hand crankcase. Thanks

I am in the process of rebuilding an 81xs400 and am having a hard time finding some parts. I am looking for the shaft with the attached hooks that are underneath the sea, used to hold down and lock the seat. My current seat is in great shape, so I don't want to buy a new seat from ebay for $75, since I just need this one part. I was hoping that someoe may have an extra lying around if they replaced a seat. If not I will have to build one by welding a hook on a shaft and if anyone has a photo of the hook or an outline please post a photo. Thanks

I am in the process of getting an old 81xs400 back on the road. It hadn’t been started in over 10years, however I have it idling now. Here is what I suggest, as I too had a similar problem. -Check the fuse box underneath the seat. My fuses looked fine however the contacts were so dirty and corroded that they would work sometimes and not others, causing a bunch of confusion. I ended up removing the existing fuse box and replacing it with individual fuses between the wires. If the electrical is not making good contact it wont fire up. -Remove the air box from the carbs and spray carb cleaner directly into the carbs. I rebuilt my carbs and replaced the jets however there were some passages that were still clogged after soaking for weeks. Make sure you can apply compressed air to all the holes in the carbs and ensure they are free. Initially my bike would only idle if I stood behind it and sprayed a carb cleaner into the carbs. It idles fine now that I cleared the passages.

I have a 1981 XS400SH and am looking for a muffler to install on the bike. The bike has head pipes that are cut behind the point where the muffler was welded on to the headers. There is a slight flare before the cut point and I can see another pipe inside. I have tried MikesXS.com and was looking at their slip-on options, however I am concerned that these mufflers may interfere with the controls. Anyone have any experience with these or can you recommend something else? I have no preference to style or sound, just looking for the cheapest solution that will not burn my valves.