Since there are always a lot of questions and things to be done when you newly acquire and old XS400, I'd like to provide everyone with a step-by-step guide. Please comment, provide corrections or suggestions.
OK, so you've got yourself a XS400. Welcome to the forum, and welcome to one of the most helpful communities I know. There are a few things you'll need to do first. Before anything else, get the manual for your model HERE. A nice overview of the helpful threads on this site can be found here.
If you run into any problems on the way, don't hesitate to ask here on the forum. Also, the google custom search function and advanced forum search are pretty good. The amount of stars next to the subject is a rough indication on how difficult the jobs are. The more stars, the higher difficulty.
0. Bike identification *
Before anything, find out if you have a DOHC or SOHC model bike, as the bikes are very similar in many ways but have distinct differences when it comes to a number of jobs. Also, parts are usually not interchangeable so keep an eye on compatibility when you order anything.
If your bike says "Maxim", "Seca", "DOHC" or "YICS" anywhere, it's likely to be a DOHC bike. These are the later model XS400 (1982-1989), of which the Seca has 6 gears instead of 5. Both the Maxim and Seca have (unless limited due to local laws and regulations) slightly more hp than the earlier XS400's. If your bike does not have any of these marks, it's likely to be a SOHC (1975-1982). If it says "Special" anywhere, it's definitely a SOHC. Of course, there has been endless modding and chopping on a lot of these bikes, so if you really want to know for sure, post some pictures on the forum and we'll help you ID your bike.
Further info on the different models of XS400's can be found here
1. Visually inspect the bike **
Before riding anywhere, whether you're looking at buying the bike from someone or you just pulled it out of a shed somewhere, check it. Use the inspections section of the manual to help you find what you're looking for. Here's the list:
- Do the tires look cracked (old rubber), is there at least 1 mm of thread still on them?
- Is the chain flexible, well-adjusted and greased?
- Is the rear brake shoe worn to the limit?
- How far are the front brake pads worn?
- Look under the seat. How are the wires doing? Use your common sense, if it's rusty and horrible, you'll know the bike is poorly maintained.
- Look under the engine for oil spills, look on the engine for drips. Some leaks may be slow, but persistent. An oily sidestand is usually indicative of leaks from clutch rod seal and/or main shaft seal.
- Look for obvious flaws, like holes in the exhaust, serious rust and things that are put together with duct tape, zipties and wire.
- Check the oil level of the bike (instructions here)
- Look for any dangerous aspects, like center- or sidestand springs missing, cables that are way too long, etc etc. Use common sense.
- Have a feel around the levers and cables on the handlebars. Clutch, choke, throttle and brake cables should feel solid and smooth, and all but the choke should spring back.
- Check if both brakes are working
- Check if the clutch works by putting it in gear and pushing the bike, with the clutch in it should be fine, without it you should have a hard time pushing it through the compression (in 1st gear, that is).
- Check the teeth of your sprockets. They should be a bit pointy (not rounded off) and should definitely not look like shark fins or waves (asymmetric is bad). Yank on the chain at the far rear of your bike (halfway the rear sprocket). The chain should not come off the sprocket more than half an inch. If it does, the chain is stretched to the limit.
- Check if there is fuel in the tank. If it's older than 2 months, drain it and put in fresh fuel (get non-ethanol fuel if you can, ethanol deteriorates the rubber boots and seals on our bikes).
- Check for free play on any of the bearings. Push the front wheel against a wall to check the steering head for free play. Yank sideways on the wheels, just check if everything is solid. You don't want to realize your rear wheel is loose when going 80 mph on the freeway.
- Check the rubber intake boots. Weathered and cracked ones likely mean they leak and the bike won't idle right until they are replaced. Intake boots that are covered in silicone, gasket sealant, or anything else, are likely cracked under all that gunk and leaking. Also look for broken bolts and missing/loose/broken clamps, cracked/missing vacuum hose to the petcock, cracked/missing vacuum cap on the right intake vacuum port. All of this will mess with air/fuel mixture in unpredictable ways and make the bike not run right.
- Check the brake hoses for damage and weathering. On OE rubber hoses look for a little plastic ring - it has manufacture date stamped in it. Some hoses have the date printed on them. Yamaha says brake hoses are good for 4 years from date of manufacture. Yours have likely been there for 35. Consider replacing them even if they don't have obvious damage, they can rot on the inside.
2. Electrics *
Put the key in, turn on the ignition and check the electrics. If it's a barn find, you might want to replace and/or charge the battery before hand either way.
- Did the oil indicator light go on for a second?
- Does the neutral indicator light work?
- Do the headlight and tail light work?
- Does the high beam work (both switches, signal light and high/low beam)?
- Does the brake light work on both brakes?
- Do the turn signals work?
- Does the horn work?
- Take out the spark plugs and have a look. Here's how you 'read' plugs. Put some new ones in, regardless of what the old ones look like.
- Check the fusebox, or, better yet, replace it with a modern ATO/ATC blade fuse box. The clips in the old Yamaha fuseboxes get brittle, which makes them lose contact or break, causing weird electrical issues and potentially stranding you on the side of the road.
3. Give it a try *
Try to start. Make sure the killswitch is not on, that won't help. Try the electric starter (if you have one) first. If it runs, do a happy dance and go for a little ride. If not (or it barely runs and stalls), continue at 4. If it doesn't even turn over on the electric starter, measure the battery voltage and troubleshoot from there. Search/post on the forum for more help, and look in your manual. In any case, continue at 4.
4. Carburetors **
Watch these videos. Take off the carbs and clean them. Unless the PO is on the forum and knows what he/she is doing, they're most likely dirty. These infamous carbs are the biggest cause of problems on these bikes, every XS400 owner has had to deal with dirty carbs at one point. Here is another handy post on cleaning. Even if your bike is running, it's a good idea to clean them. 9 out of 10 bikes on this forum which are not running, running poorly, have starting issues, or stall sometimes, can be fixed by cleaning the carbs.
Here is an exploded view of some '79 and earlier carbs, to help put everything back together.
5. Fuel filter *
Install one. Seriously. And install it the right side up. Find out how here. It'll keep your carbs out of trouble for a long long time, and for $3 and 5 minutes work you'll regret it if you don't.
6. Engine oil change *
Do one. Even if the PO says he changed it last week, you can't be sure enough with oil. Take out the oil filter too and change that. Put in something like 10W40 motorcycle oil, just make sure it's suited for wet clutches. Read about oil changing here and about different oils to use here. In short, the 20w40 (SOHC engines) or 10w30 (DOHC engines) recommended in the manual is fine, but since these bikes were made there have been newer and better oils developed. Make sure you don't over torque the oil filter bolt, use a torque wrench if you can. This goes for a lot of other bolts as well, but the oil filter bolt has been notorious for being made of butter.
7. Air filter *
SOHC bikes have two filters, one under each side cover. Check them. They are oiled foam type. If the foam is good, wash and re-oil. If the foam is rotted, replace or re-foam the filter. UNI sells foam in sheets. This is especially important for barn bikes where it is likely disintegrated, you don't want the chunks gumming up carburetors.
DOHC bikes: Open the air filter box (left side under the side panel) and inspect it. Clean out the critters, crabs and spiders by blowing air through it. If that doesn't seem to get it clean, replace it.
8. Front fork oil change *
Follow the manual for this. You can use the recommended 10w30 for it (what the manual says) but nowadays there are all sorts of options for front fork specific oil. I used a 10W front fork oil by Eurol.
CONTINUE ON NEXT POST
OK, so you've got yourself a XS400. Welcome to the forum, and welcome to one of the most helpful communities I know. There are a few things you'll need to do first. Before anything else, get the manual for your model HERE. A nice overview of the helpful threads on this site can be found here.
If you run into any problems on the way, don't hesitate to ask here on the forum. Also, the google custom search function and advanced forum search are pretty good. The amount of stars next to the subject is a rough indication on how difficult the jobs are. The more stars, the higher difficulty.
0. Bike identification *
Before anything, find out if you have a DOHC or SOHC model bike, as the bikes are very similar in many ways but have distinct differences when it comes to a number of jobs. Also, parts are usually not interchangeable so keep an eye on compatibility when you order anything.
If your bike says "Maxim", "Seca", "DOHC" or "YICS" anywhere, it's likely to be a DOHC bike. These are the later model XS400 (1982-1989), of which the Seca has 6 gears instead of 5. Both the Maxim and Seca have (unless limited due to local laws and regulations) slightly more hp than the earlier XS400's. If your bike does not have any of these marks, it's likely to be a SOHC (1975-1982). If it says "Special" anywhere, it's definitely a SOHC. Of course, there has been endless modding and chopping on a lot of these bikes, so if you really want to know for sure, post some pictures on the forum and we'll help you ID your bike.
Further info on the different models of XS400's can be found here
1. Visually inspect the bike **
Before riding anywhere, whether you're looking at buying the bike from someone or you just pulled it out of a shed somewhere, check it. Use the inspections section of the manual to help you find what you're looking for. Here's the list:
- Do the tires look cracked (old rubber), is there at least 1 mm of thread still on them?
- Is the chain flexible, well-adjusted and greased?
- Is the rear brake shoe worn to the limit?
- How far are the front brake pads worn?
- Look under the seat. How are the wires doing? Use your common sense, if it's rusty and horrible, you'll know the bike is poorly maintained.
- Look under the engine for oil spills, look on the engine for drips. Some leaks may be slow, but persistent. An oily sidestand is usually indicative of leaks from clutch rod seal and/or main shaft seal.
- Look for obvious flaws, like holes in the exhaust, serious rust and things that are put together with duct tape, zipties and wire.
- Check the oil level of the bike (instructions here)
- Look for any dangerous aspects, like center- or sidestand springs missing, cables that are way too long, etc etc. Use common sense.
- Have a feel around the levers and cables on the handlebars. Clutch, choke, throttle and brake cables should feel solid and smooth, and all but the choke should spring back.
- Check if both brakes are working
- Check if the clutch works by putting it in gear and pushing the bike, with the clutch in it should be fine, without it you should have a hard time pushing it through the compression (in 1st gear, that is).
- Check the teeth of your sprockets. They should be a bit pointy (not rounded off) and should definitely not look like shark fins or waves (asymmetric is bad). Yank on the chain at the far rear of your bike (halfway the rear sprocket). The chain should not come off the sprocket more than half an inch. If it does, the chain is stretched to the limit.
- Check if there is fuel in the tank. If it's older than 2 months, drain it and put in fresh fuel (get non-ethanol fuel if you can, ethanol deteriorates the rubber boots and seals on our bikes).
- Check for free play on any of the bearings. Push the front wheel against a wall to check the steering head for free play. Yank sideways on the wheels, just check if everything is solid. You don't want to realize your rear wheel is loose when going 80 mph on the freeway.
- Check the rubber intake boots. Weathered and cracked ones likely mean they leak and the bike won't idle right until they are replaced. Intake boots that are covered in silicone, gasket sealant, or anything else, are likely cracked under all that gunk and leaking. Also look for broken bolts and missing/loose/broken clamps, cracked/missing vacuum hose to the petcock, cracked/missing vacuum cap on the right intake vacuum port. All of this will mess with air/fuel mixture in unpredictable ways and make the bike not run right.
- Check the brake hoses for damage and weathering. On OE rubber hoses look for a little plastic ring - it has manufacture date stamped in it. Some hoses have the date printed on them. Yamaha says brake hoses are good for 4 years from date of manufacture. Yours have likely been there for 35. Consider replacing them even if they don't have obvious damage, they can rot on the inside.
2. Electrics *
Put the key in, turn on the ignition and check the electrics. If it's a barn find, you might want to replace and/or charge the battery before hand either way.
- Did the oil indicator light go on for a second?
- Does the neutral indicator light work?
- Do the headlight and tail light work?
- Does the high beam work (both switches, signal light and high/low beam)?
- Does the brake light work on both brakes?
- Do the turn signals work?
- Does the horn work?
- Take out the spark plugs and have a look. Here's how you 'read' plugs. Put some new ones in, regardless of what the old ones look like.
- Check the fusebox, or, better yet, replace it with a modern ATO/ATC blade fuse box. The clips in the old Yamaha fuseboxes get brittle, which makes them lose contact or break, causing weird electrical issues and potentially stranding you on the side of the road.
3. Give it a try *
Try to start. Make sure the killswitch is not on, that won't help. Try the electric starter (if you have one) first. If it runs, do a happy dance and go for a little ride. If not (or it barely runs and stalls), continue at 4. If it doesn't even turn over on the electric starter, measure the battery voltage and troubleshoot from there. Search/post on the forum for more help, and look in your manual. In any case, continue at 4.
4. Carburetors **
Watch these videos. Take off the carbs and clean them. Unless the PO is on the forum and knows what he/she is doing, they're most likely dirty. These infamous carbs are the biggest cause of problems on these bikes, every XS400 owner has had to deal with dirty carbs at one point. Here is another handy post on cleaning. Even if your bike is running, it's a good idea to clean them. 9 out of 10 bikes on this forum which are not running, running poorly, have starting issues, or stall sometimes, can be fixed by cleaning the carbs.
Here is an exploded view of some '79 and earlier carbs, to help put everything back together.
5. Fuel filter *
Install one. Seriously. And install it the right side up. Find out how here. It'll keep your carbs out of trouble for a long long time, and for $3 and 5 minutes work you'll regret it if you don't.
6. Engine oil change *
Do one. Even if the PO says he changed it last week, you can't be sure enough with oil. Take out the oil filter too and change that. Put in something like 10W40 motorcycle oil, just make sure it's suited for wet clutches. Read about oil changing here and about different oils to use here. In short, the 20w40 (SOHC engines) or 10w30 (DOHC engines) recommended in the manual is fine, but since these bikes were made there have been newer and better oils developed. Make sure you don't over torque the oil filter bolt, use a torque wrench if you can. This goes for a lot of other bolts as well, but the oil filter bolt has been notorious for being made of butter.
7. Air filter *
SOHC bikes have two filters, one under each side cover. Check them. They are oiled foam type. If the foam is good, wash and re-oil. If the foam is rotted, replace or re-foam the filter. UNI sells foam in sheets. This is especially important for barn bikes where it is likely disintegrated, you don't want the chunks gumming up carburetors.
DOHC bikes: Open the air filter box (left side under the side panel) and inspect it. Clean out the critters, crabs and spiders by blowing air through it. If that doesn't seem to get it clean, replace it.
8. Front fork oil change *
Follow the manual for this. You can use the recommended 10w30 for it (what the manual says) but nowadays there are all sorts of options for front fork specific oil. I used a 10W front fork oil by Eurol.
CONTINUE ON NEXT POST
Last edited:
Try to use the biggest diameter tube you can, while still being able to attach it properly (air tight) to the vacuum ports (use zip ties or something). If the tube is too thin, you'll get air bubbles in the oil and you'll never be able to sync well.
