-
Enjoy XS400.com? Consider making a donation to help support the site.
XS400.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
1981 xs400 cafe repair/rebuild
- Thread starter adrian
- Start date
Also make sure it is ethanol resistant.
Definitely looks too small. Should be 1/4" inside diameter. Almost looks like 1/4" OD.
You'll want to press it all the way onto each fitting, if you can, and throw on some tube clamps.
You'll want to press it all the way onto each fitting, if you can, and throw on some tube clamps.
Pulled the bike out today and fired her up…still running poorly after the carb cleaning and valve adjustment. My guess is a vacuum leak with the carbs and I've linked 2 videos if anyone wants to chime in.
She's basically running the same as before, right side not firing consistently and bogging out with throttle. The hesitation you hear in the video is when I'm giving it slight throttle twice and then it stalls (the right side has come to life when throttling up slightly and holding until it begins firing on both cylinders.)
The second video is a longer take with it sounding a little better but running just as shitty.
She's basically running the same as before, right side not firing consistently and bogging out with throttle. The hesitation you hear in the video is when I'm giving it slight throttle twice and then it stalls (the right side has come to life when throttling up slightly and holding until it begins firing on both cylinders.)
The second video is a longer take with it sounding a little better but running just as shitty.
All the jets are stock. Pulled the carbs to drill out the EPA caps and re-set the pilot jet 3 turns out. I ordered two more sets of jets, 145 and 147's just to be safe. UNI filters were straight out of the box, so I'm assuming they were oiled from the factory. I'll post more info. once I make more tweaks to the carbs.
Rambo814
XS400 Addict
Video #2 kinda sounds like vacuum leak. Are the carb manifolds ok? (between carbs and jugs)
Filters need to be oiled.
I forgot to mention I pulled the motor from the $50 donor bike last week. It's a '78 running points and from what I've read on the forum, I hope it's not a royal pain in the ass swapping in the electronic ignition with the engine harnesses being slightly different.
At this point on my '81, I'm pretty much giving up the motor. As I found out early on, the kickstart journal was broken by the PO (and had a dead starter motor.) I was going to swap in the e-start from the '78 but that seems stupid to pull that, when it won't take me much longer to swap the entire engine.
The '81 motor is what you've seen in the videos and it's beginning to be a huge headache getting it running right, with the fucked up kickstarter to boot. The kickstarter got locked up the other day and I didn't have any luck when I pulled/reinstalled it. I know I shouldn't be using it but I figured I've got the other motor, so I really don't care if this one gets any more messed up.
Still waiting for the new jets to come in (145, 147's) and I ordered spray oil for the UNI filters. I'll probably be tearing into the '78 carbs now too since they've got the nicer idle air adjusters, which will make it easier to tune with the tank on.
This whole process has been slow-going since I wasn't able to rent a garage this winter, so waiting it out for warm weather was necessary. The donor bike is at my house and the cafe is at work, so wrenching on the cafe hasn't happened as much as I've liked. There's not a great workspace where I work and let's be honest, I'd rather be working on something at home than staying super late days at the office.
To be continued...
At this point on my '81, I'm pretty much giving up the motor. As I found out early on, the kickstart journal was broken by the PO (and had a dead starter motor.) I was going to swap in the e-start from the '78 but that seems stupid to pull that, when it won't take me much longer to swap the entire engine.
The '81 motor is what you've seen in the videos and it's beginning to be a huge headache getting it running right, with the fucked up kickstarter to boot. The kickstarter got locked up the other day and I didn't have any luck when I pulled/reinstalled it. I know I shouldn't be using it but I figured I've got the other motor, so I really don't care if this one gets any more messed up.
Still waiting for the new jets to come in (145, 147's) and I ordered spray oil for the UNI filters. I'll probably be tearing into the '78 carbs now too since they've got the nicer idle air adjusters, which will make it easier to tune with the tank on.
This whole process has been slow-going since I wasn't able to rent a garage this winter, so waiting it out for warm weather was necessary. The donor bike is at my house and the cafe is at work, so wrenching on the cafe hasn't happened as much as I've liked. There's not a great workspace where I work and let's be honest, I'd rather be working on something at home than staying super late days at the office.
To be continued...
Attachments
Robsteeler66
XS400 Addict
Just wondering, why not just pick up an electric starter off of ebay and put it in the current motor. Pretty much every bike today is just electric start and this one is only $37.
http://www.ebay.com/itm/Yamaha-XS40...ter-/360495955627?hash=item53ef3bbeab&vxp=mtr
http://www.ebay.com/itm/Yamaha-XS40...ter-/360495955627?hash=item53ef3bbeab&vxp=mtr
Update # too many…swapped in the starter from the '78 engine to the '81, since I decided against the motor swap for the time being. Pulled the carbs completely apart and I'm pretty sure I found my issue, torn diaphragms! The right side had three tears in it that had been patched at some point but worn through again. Left side had one tear, so this explains my vacuum leak(s)
There were also no O-rings on the pilot jet screws, only the left side had a small washer underneath the spring. I can't imagine that if there were O-rings originally that they would have deteriorated to nothing. These carbs had the brass inserts covering the pilots, so I would have to assume that's exactly how they came from the factory?
I ordered new diaphragms from JBM and also re-ordered new main jets. Found out mine were 135's and I had gone by the books standard of 142.5. I had originally purchased 145's and 147's but they would be way to rich for my setup. The bike only has pod filters, so the step up to 137.5 should do the trick. Now just have to wait for the diaphragms and jets to come in!
There were also no O-rings on the pilot jet screws, only the left side had a small washer underneath the spring. I can't imagine that if there were O-rings originally that they would have deteriorated to nothing. These carbs had the brass inserts covering the pilots, so I would have to assume that's exactly how they came from the factory?
I ordered new diaphragms from JBM and also re-ordered new main jets. Found out mine were 135's and I had gone by the books standard of 142.5. I had originally purchased 145's and 147's but they would be way to rich for my setup. The bike only has pod filters, so the step up to 137.5 should do the trick. Now just have to wait for the diaphragms and jets to come in!
Attachments
[pic heavy update]
So, my bike is finally running, and running pretty well at that! I took it home from work on Sunday and rode it 15 miles back to my place. It stalled once half an hour into the trip at idle but started right back up without any issues.
As for the fixes…got the diaphragms from JBM and they fit perfectly. The site is a little crazy as far as measuring goes. I checked mine and it didn't match what they were saying for the BS34's but I figured, fuck it, it's gotta be right (I also didn't have calipers, just a crappy ruler.) It ended up being spot on, thankfully. I had to crack off the old plastic clips with wire dykes in order to put the new ones on. All you have to do is follow their directions for matching up the holes in the slides to the engine side.
It took me 3 tries to get the correct main jets for these bad boys. The second go round I got the air jets instead of mains…ended up buying the 137.5 mains from MikesXS as well as 2 little kits with needle jets, o rings, springs, washer and blind plugs.
Getting the bike started up wasn't too tricky but I was pretty hungover working on it and initially forgot to connect the vacuum line from the tank to the right side carb
I ended up realizing it that night and came back to it with a fresh head the next day. I had a little trouble getting it to kick over and ended up putting it to prime several times while cranking and then it finally went (there was some air in the gas line from not connecting the vacuum line initially.)
For the carbs, I bench synced them before putting them on and set the idle mix screws at 3 turns out. Once I got the bike started the idle was way too high, so I adjusted the idle stop knob and cut the mix screw to 2 turns out….it took about 3 or 4 tries to get this all right, pulling the tank each time. Also oiled the UNI filters! @xchris
Once the bike was idling successfully and throttling up with no hesitation, I rode it around my work's parking lot for about 30 minutes with no issues. Once I did stop, I realized I had a decent oil leak coming from the bottom of the alternator cover.
I'll admit it, I got lazy when I swapped in the new starter motor and re-used the old gasket. The bottom allen bolt had punctured through the gasket and I probably lost 1/2 a quart from it sitting overnight. Luckily, I had a new gasket and slapped it on the following day and voila, oil leak fixed
I've had the bike out twice since I've got it running good and the only hang up I've noticed is that the idle won't drop right away when I really go hard (rev out) on it for a while. For instance, I'm in the city so I won't start out in first, just do a rolling stop in second and rev up to 5 or 6K to the next light or stop sign (block to block.) It will drop down if I let it sit for a minute but I'm not too concerned overall. I'll probably lube up the throttle cable, in case that what's hanging up.
I'll put some videos of her running in the next post
So, my bike is finally running, and running pretty well at that! I took it home from work on Sunday and rode it 15 miles back to my place. It stalled once half an hour into the trip at idle but started right back up without any issues.
As for the fixes…got the diaphragms from JBM and they fit perfectly. The site is a little crazy as far as measuring goes. I checked mine and it didn't match what they were saying for the BS34's but I figured, fuck it, it's gotta be right (I also didn't have calipers, just a crappy ruler.) It ended up being spot on, thankfully. I had to crack off the old plastic clips with wire dykes in order to put the new ones on. All you have to do is follow their directions for matching up the holes in the slides to the engine side.
It took me 3 tries to get the correct main jets for these bad boys. The second go round I got the air jets instead of mains…ended up buying the 137.5 mains from MikesXS as well as 2 little kits with needle jets, o rings, springs, washer and blind plugs.
Getting the bike started up wasn't too tricky but I was pretty hungover working on it and initially forgot to connect the vacuum line from the tank to the right side carb
I ended up realizing it that night and came back to it with a fresh head the next day. I had a little trouble getting it to kick over and ended up putting it to prime several times while cranking and then it finally went (there was some air in the gas line from not connecting the vacuum line initially.)For the carbs, I bench synced them before putting them on and set the idle mix screws at 3 turns out. Once I got the bike started the idle was way too high, so I adjusted the idle stop knob and cut the mix screw to 2 turns out….it took about 3 or 4 tries to get this all right, pulling the tank each time. Also oiled the UNI filters! @xchris
Once the bike was idling successfully and throttling up with no hesitation, I rode it around my work's parking lot for about 30 minutes with no issues. Once I did stop, I realized I had a decent oil leak coming from the bottom of the alternator cover.
I'll admit it, I got lazy when I swapped in the new starter motor and re-used the old gasket. The bottom allen bolt had punctured through the gasket and I probably lost 1/2 a quart from it sitting overnight. Luckily, I had a new gasket and slapped it on the following day and voila, oil leak fixed
I've had the bike out twice since I've got it running good and the only hang up I've noticed is that the idle won't drop right away when I really go hard (rev out) on it for a while. For instance, I'm in the city so I won't start out in first, just do a rolling stop in second and rev up to 5 or 6K to the next light or stop sign (block to block.) It will drop down if I let it sit for a minute but I'm not too concerned overall. I'll probably lube up the throttle cable, in case that what's hanging up.
I'll put some videos of her running in the next post
Attachments
Last edited:
VIDEOS
https://instagram.com/p/3AAAN0ImcP/?taken-by=_barno_
(idle/throttle response good)
https://instagram.com/p/3FbveRImdi/?taken-by=_barno_
(parking lot test ride)
(idling after riding for 30 minutes)
(from initial startup, idle too high)
Put up a photo of the oil leaking from the alternator side of the bike. Replaced gasket and she was good as new.
https://instagram.com/p/3AAAN0ImcP/?taken-by=_barno_
(idle/throttle response good)
https://instagram.com/p/3FbveRImdi/?taken-by=_barno_
(parking lot test ride)
Put up a photo of the oil leaking from the alternator side of the bike. Replaced gasket and she was good as new.
Attachments
Reviving an old thread here. Going to do the motor swap about a year after I got this thing running. The old motor has been okay but I recently posted about some ignition gremlins that I can't track down. Seems like the TCI is dying as I'm not getting a good spark on the right cylinder. The motor kicks over but barely idles at half choke and the right plug has no sign of firing. Tested coils and they checked out and even bought a spare, which also checked out okay. On top of the TCI issue, the OG motor burns oil like mad and started a nice leak at the top end a few months back. It's also got the dreaded broken kickstart journal to boot.
Since the TCI's are hard to come by and if you can find them, cost upwards of $300, I'm going to take my chances with the $10 spare motor. Ironically enough, the spare motor was locked up when I looked at it the other day but I got it moving again soaking the heads with WD-40. Going back in time to points/condensor on this one. I'll post updates of the swap as it goes in. Pic is of current motors leaky head.
Since the TCI's are hard to come by and if you can find them, cost upwards of $300, I'm going to take my chances with the $10 spare motor. Ironically enough, the spare motor was locked up when I looked at it the other day but I got it moving again soaking the heads with WD-40. Going back in time to points/condensor on this one. I'll post updates of the swap as it goes in. Pic is of current motors leaky head.
Attachments
So this project turned into more of hassle then I predicted but it's pretty much back on track after about a month of futzing with it. There were some typical pitfalls/unknowns that came up during the project, which I'll list below:
-Rear motor mount on the '81 is bigger than the '78. I can remember when I pulled the '78 motor it had the rear motor mount bolt set up top vs. the '81 was at the bottom. Went to a local shop to machine the old bolt down and they pointed me in the direction of Fastenal, a company that primarily deals with custom bolts and whatnot. Took two tries but finally got something that fit (3/8 by 9 or 10".) Cost of $9
-Didn't remember to pull the condenser off the '78 so I had to buy a used one. Tested bad and bought another one off MikesXS to no avail. Had some spark on the right cylinder but nada on the left. Re-tested coils and found they were bad (primary read 6 ohms and secondary nothing) 2 condensers around $30 total.
-When the condenser tested bad I also ordered another set of points since my OG's were slightly blackened. $19
-Dead coils equals new ones from MikesXS. $69
-Thankfully I had the wire loom from the '78. I pulled out a lot of unnecessary crap that was still on the bike (no signals, horn, TCI harness, couple flasher relays.) I just nipped the points wiring off the '78 loom and spliced it into the '81 harness. Also cheated and used that stator off the '81 but from the wiring diagram it shouldn't have been an issue from '78 to '81 but better safe than sorry (3 wire stator vs 4 wire.) Extra wire was just for the headlight but didn't want to mess with it if I didn't have too. $0
$127 bones isn't too bad considering I could get a TCI for possibly that price but knowing that if the points fail, it's not an expensive fix.
In the beginning of the process I decided to make the bike kick-only (less wires, cleaner look, less weight with no starter motor.) I also wanted to do it since the '81 engine had a cracked journal, thus making the kick-start useless. I had the battery die on me a couple times with only the starter motor to rely on and never want to bump start this bike again! I went with the freeze plug route for the starter motor block off based on a thread here. Hoping that it doesn't fail, though. Right after I did it, I saw a post from a local bike shop about a freeze plug blowing out on a ride and spewing oil everywhere.
Pics show a choppy process of the swap. The picture of the condenser is interesting because thankfully, the '81 still had a mounting point tab for it even though it wasn't used in the TCI ignition. Another pic illustrates the mounting point for the '78 engine and also an example of the OG '81 motor mount bolt vs. what I had to get to fit the '78 on the lower rear.
I'll do another update this coming week. Coils are supposed to come Monday and hopefully she'll be turning over that day too.
Attachments
If you are using an 81 frame you must use the 81 lower engine bolt and dampers. The 81 frame don't have a upper (and lower) rear motor mount like the 78 and will need the stronger lower bolt. It only has a lower. You will need to drill out the case hole to fit that larger bolt. The 81 motor/frame mounts is meant to have more movement to absorb the vibes of the engine.
Last edited:
