1st post: just acquired XS400

[Lemonysword]

I just picked this XS400 up from my buddy for $500. Brief history on the bike is that he bought it from the original owner, who hadn’t ridden it in years, about four years ago. He wasn’t able to ride it until about two years ago and only rode it for the summer. He did put new tires on it and told me that his friend “cleaned the carbs,” but who knows if he truly cleaned them. It’s been sitting in his (unheated) garage ever since.

We got it to run on some fresh gas, but after a while it refused to run unless the throttle was held open. The intake boots are cracked pretty badly, so I suspect that is the main problem. I tried to take it around the block yesterday and it maxed out at 2000rpm going maybe 5mph at wide open throttle.

First order of business is to clean and rebuild he carbs, replace the intake boots, put new air filters in, and replace the fuel and vacuum line. The tank also has some very minor rust, though that is an easy fix with evaporust. Is there anything else I should do while I’ve got it pulled apart? Anything special or unique quirks about these bikes I should know?

 

[xschris]

Welcome to the forum. The bike is a 80-SG and looks very stock and original. That will help with getting it running and keep it running it's best. Nice find! You don't see them like this much anymore.

 

[Lemonysword]

Welcome to the forum. The bike is a 80-SG and looks very stock and original. That will help with getting it running and keep it running it's best. Nice find! You don't see them like this much anymore.

Thanks, I know the Japanese bikes from this era run best when bone stock, for the most part. I’ve seen some really good looking builds people have done off these bikes (pic related, it’s simple but incredibly aesthetic), and while I’d love to do that, I’d hate to ruin an increasingly uncommon bike. This bike makes me want to watch Terminator and hook up with a girl with big hair listening to Motley Crue.

The only thing I’m considering changing is jetting up. I know pretty much every import comes very lean from the factory due to the EPA, so I’d like to know if there’s a recommended jetting size for these bikes in stock config.

 

[Specdog]

Very nice original XS. I can't see anything cosmetically wrong. I get a kick out of those wheelbarrow handlebars, I'm OK with them. I run stock jetting in my original and don't see a lean problem. If you think you want to enrichen the fuel, turn the mixture screws out to three turns. That might satisfy your issue. The engine is robust, so no known historical headaches to deal with, just the routine things that happen to 40 year old motorcycles. Bleed the brakes with fresh fluid, and consider changing the line and rebuilding the caliper and MC. Welcome to our little forum.

 

[xschris]

These don’t need any larger jets if the bike is stock. Like specdog said just turn out pilot mix screws to three and that’s about it. I have five of these bikes and they run just fine that way.

 

[Lemonysword]

Ok, thanks for the info gents. I haven’t done a ton of research yet, just wanted to check that box off so I knew whether to order jets or not. If they run wel stock then I will leave it.

I definitely need to dunk the carbs and throw a new boot on. I noticed earlier today that the left boot has been replaced, but the right is factory with the original rusty screws and all. It’s incredibly cracked so I’m sure lots of air is leaking in there.

 

[xschris]

Make sure to fully take the carbs apart before putting them into any harsh solution. Shaft seals should be replaced as well as any rubber bits. Make sure the diaphragms are not cracked or have holes in them. jetsareus.com has real mikuni jets. Always use real mikuni jets as the aftermarket stuff is poorly made and the sizes can be off.

 

[Lemonysword]

Got a link to quality rebuild kits? I doubt I’ll need jets if the stock ones are good, but pretty much every rebuild kit I’m seeing is from Taiwan

 

[xschris]

I don't buy kits just the parts I need as the quality is better and can get better deals. https://www.ebay.com/itm/Suzuki-GS850G-GS1000-GS1100-GS1150E-Carburetor-Carb-Idle-Passage-Plugs-Set-of-4/163472474277?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649 Pilot jet plugs. https://www.ebay.com/itm/4-Bowl-gaskets-82-XJ1100-80-81-XS1100-80-83-XS650-ALL-gasket/192162418602?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649 Bowl gaskets. https://www.ebay.com/itm/PAIR-of-1980-1984-XS650-Float-Valve-O-RINGS-8F2-14147-00-00-XS-650-BS34-carb/182034756195?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649 Float seat o-rings. If your float needles are beyond service I would just replace the entire assembly. https://www.ebay.com/itm/Yamaha-25G...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

 

[MoonClipper]

Welcome to the forums! I love the retro luggage rack you have in your bike. Good luck with getting it running right!

 

[Lemonysword]

Thanks guys. I tore into the carbs tonight, what a fuckin' nightmare. My friend assured me that his buddy did a proper cleaning of the carbs when he first acquired the bike 4 years ago. Not a chance in hell he even cracked them open. The gasket was ancient and brittle. I had to dremel a slot in one of the top cover screws and use a fat flathead to get it out. One of the float pins is seized, punching did nothing. The screw holding the float needle valve in place on the carb whose float I was able to remove is also seized. I have JIS screwdrivers, and an impact driver with a JIS bit. It only helped me on one of the top cover screws. I doused it all in liquid wrench and left for the night before I really bugger a screw I don't want to bugger.

On the plus side, both pilot and main jets came out easy, and the diaphragms look to be in excellent shape.

I just rebuilt the Mikuni carb on a 1981 Suzuki GN400 that had been rebuilt maybe 10, 15 years ago. It was incredibly easy. That one is essentially a slightly larger version of this carb.
https://imgur.com/gallery/wgpbYV7

 

[MoonClipper]

My guess is his buddy simply cleaned the float bowls, and at the time the gasket was probably usable by his standards so he reused it.

Good luck with the carb rebuild, they look like a nightmare!

 

[Lemonysword]

Welp. More fun tonight boys. I've got it all apart except for the pilot screw and the actual bracket holding it together.

I discovered something absurdly strange. In the part of the body that holds the needle and main jet, there is a small brass plug near the bottom that seems to fit into the notch on the needle jet to keep it from rotating. IT'S FUCKING MISSING on one of the carbs. I don't know what it is called, or where I would even start to look for one to replace it with.

https://imgur.com/gallery/URguhrQ

 

[Yellow0206]

Welcome to forum - i got my XS400 last year and did mostly cosmetic mods, not mechanical, but did a lot of mechanical work on deferred maintenace and some repairs - some tips from me based on experience / mistakes I or PO made that i discovered so you can try to avoid:
1) when you replace oil filter be cautious not to overtighten the bolt for the filter housing - mine was cracked slightly when i got it and very cery tight and got worse when i took off so i had to replace lucky i found NOS one cheap
2) your instinct about running best stock is correct - only thing not stock on mine is exhaust and ive got mine tuned almost perfectly but i think non stock exhaust is culprit for a small remaining issue i have at high rpm
3) as xschris said dont buy full carb rebuild kit you will likely grt unneeded and poor quality parts - get the stock jets parts where possible and i have found K&L and Emgo - both are longstanding Japan/Taiwan (K&L) or Taiwanese (Emgo) mfgs of high quality aftermarket parts - do not confuse Taiwan (“kinda China”) with Mainland China - i have had bad experience with latter, good with former...
4) if/when you have issues do try to diagnose rather than throwing parts at it - i have done a bit of the latter and while it made me replace a lot of maintenance items which is good in a way, i spent more than i needed for example i have new coils I likely did not need
5) set float height carefully and make sure your petcock does not leak - one or both can get you extra gas in your engine that will end up in your oil/crankcase which is not good - smelled gas in oil when i got mine and petcock was indeed leaking and floats not set right
6) Also be careful with left side cover bolt tightness - this is another crackable item - mine has a tiny crack from PO and I JB welded it in meantime as I try to source reasonably priced NOS or used
7) in terms of getting carbs on and off - first time took me like 4 hours, now i can do in 45 mins or less - keep tank and seat off, take air filters out completely, (assuming you have in yours mine is 77) put breather tube on both the carb to air filter manifold and crankcase first on reinstalling it, and put it in place then squeeze carbs in, have all clamps on but as loose as possible with clamp bolts starting on threads and pushed forward or backward

Hope this helps things go smoother for you. I am sure you will enjoy the bike...

 

[Lemonysword]

Well. Finally got the two carbs apart. My impact driver and propane torch were heavily used, an extractor kit was completely useless, and even then, two of the big screws on top needed a big slot cut in and a large flathead to remove them. Wow.

so my only thing left to do is pull the brass cap off the pilot screw, which so far has been impossible. Heating and pulling has been fruitless. I don’t think it’s moved. I even put the screw i stuck in it in my vice and pulled on the carb as hard as I could, to no avail.

 

[NewHavenMike]

Going to town on that thing!

Now would be the time to invest in a decent set of tools. The phillips screws are actually JIS and use a slightly different head, just so you know. Practically everyone uses normal tools anyways but the JIS drivers fit like a key.

Im pretty sure those plugs get drilled out. I havent had to do this to my carbs but the general consensus is that carbs and drill bits do not mix well together. Youre playing with fire haha.

 

[xschris]

I would avoid any heat as the rubber o-rings will get damaged. The plugs get drilled out going very slow and by starting with a smaller size then going to the size of the plug. The plug is only an eighth inch thick so don’t go any more than that. Most of the plugs I have removed come out before I get to the size of it.

 

[Lemonysword]

Going to town on that thing!

Now would be the time to invest in a decent set of tools. The phillips screws are actually JIS and use a slightly different head, just so you know. Practically everyone uses normal tools anyways but the JIS drivers fit like a key.

Im pretty sure those plugs get drilled out. I havent had to do this to my carbs but the general consensus is that carbs and drill bits do not mix well together. Youre playing with fire haha.

My JIS screwdrivers were ineffective as well. So far the only things that didn’t need heat, impact driver, or having a slot cut in them were about half of the top cover and float bowls crews. Surprisingly the jets came right out. Idk why this one is so, so incredibly difficult. I just rebuilt a 1980 GN400 and the carb opened right up for me.

I will try drilling this out. I put tape on my small bit to drill the initial hole, only exposed 5mm of the bit. I’ll opening it up since my method is not working. This needed to happen though, these carbs were disgusting and dirty with actual dirt and grime.

too late to not use heat, but I’ve got new O rings coming so I don’t care too much. I’m excited now to see if my air screw tips are broken (probably are). That’ll be another fun challenge. I was hoping to get this running this week, but it has fought and fought and fought every step of the way.

 

[Lemonysword]

The four big (8 or 10mm) screws holding the bracket that attaches the carbs were the most seized screws I’ve ever encountered. I think they actually glued them in place; there was white residue in the screws hole. Two of them I was able to get out, after much heat and banging, with an impact driver. They were so seized that I had to use to impact driver til they were a quarter of the way out before I could use a screwdriver. This one I actually gave up on and was trying to cut the head off to just leave it, I was so mad. This cut goes to almost the bottom of the screw, when I decided to give it one more shot with my big flathead. Muscles popping and straining, finally it turned

 

[xschris]

The lower bracket screws are held in with a form of lock-tight. I use a set of short nose vise grips to crack them loose and any others. Just small movements at a time locking them on sideways. Be careful with the aluminum heat and banging will crack it. Stripping holes is another thing. Splitting the carbs should only be done if your going to replace the shaft seals or center hose.