Replacing 1981 XS400 Carbs

[wutwolf]

So, I bought this bike a few weeks ago. Replaced the starter motor this weekend, because I couldn't kickstart it to save my life. Now, the bike will start after a few seconds, but then will slowly wind down till it dies.
After a little research, I decided the carbs needed to be cleaned. Took them out and discovered they must have been dropped in the past because one of the bowl covers was cracked and then Bondo-ed back tight. I took the cover off, thinking, Oh, okay, that can't be that bad. Then I see that one of the brackets holding the float pin in place has cracked and is missing as well.

Long story short, I'm done with this carb. Can't find another exact replacement cheap enough. I was wondering how I would find out what other carbs would work on this bike as I'm new to this.
I saw the thread on two-to-one carbs, but don't have a welding torch or any experience. So, I'd prefer something that was more plug-n-play.
Thanks!

 

[xschris]

Any sohc xs400 carbs will work. I would look for a set of 80-82 model because the 77-79 models are not going to have all the same parts as the set you have. Any pics of what you have so maybe we can give you some ideas on how to fix them, or how bad they are

 

[wutwolf]

I went and took some pictures. I also included a picture of whatever the thing it plugs into is called. I don't know if it's relevant or not, but I figured more info is better than less.

I peeled most of the Bondo off the outside to get a better look at it.

Also, what does sohc mean?

 

[Lou Ranger]

I can answer at least one of your questions! sohc means "single overhead cam".

Was the repair made literally with Bondo or something like JB-Weld, or even an actual weld repair? The black stuff in the inside corner almost looks like silicon caulking (like GOOP or permatex gasket maker).
While the repair to the cracked bowl may not look great, are you sure that it is what is causing your winding down issue?
Before trashing the thing and spending a lot of money for a new carb, why not clean them as you would un-cracked ones, repair the broken float bowl pin holder (or guide?) with something like JB-weld or Permatex Cold Weld, and test it out.
You might find you can ride right away - letting you for look some a reasonably priced used carbs or internal parts at your leisure.

http://www.permatex.com/products/au...oxies/Permatex_Cold_Weld_Bonding_Compound.htm​

 

[wutwolf]

Whatever it was was easy enough to peel off with a fingernail. I think the stuff on the inside is the same, just darker because of grime and the way my camera captured it.

So, I would just put the weld repair on the broken pinholder, shape it accordingly and then drill a hole for the pin holder? I'm correct in assuming that if I left the pin in there it would adhere to that quite readily?

Just from my internet searching and the Hayne's manual I have, I had determined the carbs to be the most likely cause. When I took them out to clean them, I noticed all the other stuff.
Another relevant thing, I think is that the bike will leak gas if it gets too hot. That has something to do with the floats being incorrectly adjusted, yeah?
Is it normal for gas to pour out of the carb when you take it out? Cause mine did. Although it smelled more like varnish than gasoline.

 

[Lou Ranger]

...So, I would just put the weld repair on the broken pinholder, shape it accordingly and then drill a hole for the pin holder? I'm correct in assuming that if I left the pin in there it would adhere to that quite readily? ...

If it were me, and I was prepared to pay the money for a new part anyway, I would try it first out of curiosity. If it worked I'd be a genius and save the money, and if it didn't I'd be no worse off.
I would assume the pin would adhere. But what if you wrapped it in something which would never stick to the pin? Maybe Saran wrap or teflon tape. Even if a layer of tape stuck to the weld, if you wrapped it several times, the rest would come out with the pin, leaving a bit of clearance. If it was still too tight, you could use a drill bit the same size as the good hole to widen it just right.
I wouldn't consider it if it was a high stress bracket or subjected to internal engine temperatures, but unless the cold weld stuff is not compatible with gasoline, what could it hurt?

... Another relevant thing, I think is that the bike will leak gas if it gets too hot. That has something to do with the floats being incorrectly adjusted, yeah? Is it normal for gas to pour out of the carb when you take it out? Cause mine did. Although it smelled more like varnish than gasoline.

Sorry, but this I know nothing about and don't even have a crazy suggestion for it. Just to clarify for others though, when you say "take it out", do you mean take the carb out, or take the bike out for a run? If the latter, then I think I have read this symptom before and, as I recall, it is often mal-adjusted float bowls. Not sure what will be the case for you, but until one of the carb gurus writes in, try reading some threads like this one where, among other things, they reveal float-height misprints in the manuals

http://www.xs400.com/forum/showthread.php?t=4500&highlight=float+bowl+height+adjustment&page=2​

Good luck!

 

[wutwolf]

Alrighty, I'll head over to Ace tomorrow or the next day and see what's up. I'll tell you how it goes.

When I leave it in the garage on a hot day there will be a little puddle of gas underneath it. I don't know if the same thing happens when riding because the amount of gas wouldn't be noticed when riding and I haven't yet had a chance to ride it yet =(

Yeah, when I pulled the carb out to clean it, I had to tip it a bit to clear it and a bunch of gas poured out. It was an unpleasant surprise.

 

[xschris]

By the looks of the carb I would say they will need a rebuild and a good cleaning. You might be able to jb weld the pin in place but I think you might have a hard time getting it out just to be able to rebuild them in the first place. Try to get the carbs all apart to clean them first then go from there.

 

[speedsville]

I went and took some pictures. I also included a picture of whatever the thing it plugs into is called. I don't know if it's relevant or not, but I figured more info is better than less.

I peeled most of the Bondo off the outside to get a better look at it.

Also, what does sohc mean?

As Lou wrote he is right about; SOHC vrs DOHC (duel overhead cams).
So DOHC have one cam for the intake and one for the exhaust valves.
We have one cam actuating both intake and exhaust valves.

 

[wutwolf]

Well, I got it all in pieces now. Everything looked pretty clean. The only thing I noticed, aside from the previous problems, was that when I set the float bowls down a bunch of soot was shaken loose. Also, the jet screw on the broken bowl is mangled as well. I wondering if it's been maladjusted. I can't see any way salvaging it aside from screwing another screw into it, pulling it out and then replacing it.

Also, the float bowl gaskets crumbled in my hands, so if I'm to go ahead with this I'll need to replace those.

The question now becomes, is it worth it to try and get this to work or should I just look into getting a replacement of some sort?

By rebuild, do you mean get parts made to replace these broken ones?

 

[Lou Ranger]

As Lou wrote he is right about; SOHC vrs DOHC (duel overhead cams).
So DOHC have one cam for the intake and one for the exhaust valves.
We have one cam actuating both intake and exhaust valves.

How about that gigantic red thing you are standing with in your Avatar? If they put even one cam overhead on it, wouldn't it raise the centre of gravity too much?

 

[xschris]

By rebuild I mean pilot jet plugs new main and pilot jets. New float valves and seals and bowl gaskets. Oh and cleaning the crap out of every little bit of the carbs.

 

[Lou Ranger]

... when I set the float bowls down a bunch of soot was shaken loose.
Also, the float bowl gaskets crumbled in my hands ...

Yuk.
Oh, and just for future reference, the correct term (and one of our top-secret code words on the Forum) is "DETRITUS".

 

[wutwolf]

After reading about two-to-one conversions I'm seriously considering just chucking the bad carb, rebuilding the good one and making the necessary modifications.
Either that or finding a two intake(?) carb from a different model that can be made to fit with minimal modifications. I haven't had any luck finding a stock carb for anything reasonable.
Detritus. I'll have to remember that one.

 

[arfstrom]

I was just in the Motorcycle bone-yard here in Minnesota. These guys have billions of parts on hand. I went down there to get a float for my bowls, and they had it, and anything else I might need. (license plate light chrome thingy) I know this is a little far for you to day trip to, but they do have a web presence. Perhaps you can look around your neighbor hood for cycle bone-yard. phone number and you can talk to someone.
http://www.sportwheel.com/index.html Link to their eBay store is on homepage. (nothing listed for XS400) but I know they have the parts. Literally Huge crates of Carbs, some are shot, some are pristine.
Good Luck

 

[wutwolf]

Thanks for that! I sent them a part request, so we'll see what's up within a few days.
Also, I came across this nifty little resource. I don't know how current it is, but worth checking out. I'm gonna call some of these people tomorrow or the next day.
http://bikersindex.com/junkyards.html

 

[speedsville]

How about that gigantic red thing you are standing with in your Avatar? If they put even one cam overhead on it, wouldn't it raise the centre of gravity too much?

It is an SOHC, 3 valve per cyl.
Twice the weight of the Yamaha with 4.5 times the displacement and 5 times the HP.

 

[speedsville]

I was just in the Motorcycle bone-yard here in Minnesota. These guys have billions of parts on hand. I went down there to get a float for my bowls, and they had it, and anything else I might need. (license plate light chrome thingy) I know this is a little far for you to day trip to, but they do have a web presence. Perhaps you can look around your neighbor hood for cycle bone-yard. phone number and you can talk to someone.
http://www.sportwheel.com/index.html Link to their eBay store is on homepage. (nothing listed for XS400) but I know they have the parts. Literally Huge crates of Carbs, some are shot, some are pristine.
Good Luck

Here is a picture of their place you can pick out the bike you want parts for:

 

[Lou Ranger]

It is an SOHC, 3 valve per cyl. Twice the weight of the Yamaha with 4.5 times the displacement and 5 times the HP.

Wow. You are almost at both extreme ends of the spectrum. Ever wanted to own something in the middle of the Bell curve?

 

[speedsville]

Wow. You are almost at both extreme ends of the spectrum. Ever wanted to own something in the middle of the Bell curve?

LOL yeah when I do something I do something went from the 400 to the 1800, I didn't
want to make 3 steps in between. Kind of stupid, I dropped that thing a bunch of times
because it is so massive. But the fun when you twist it at 50 to 100 is blast.
My friend had a VTX and I couldn't let him have something over me.

I was just looking at 750 Shadows on Craig's list.
Also looking at Honda : Valkyrie's there.
Cheap and easy to look, but I've got enough to keep me busy now,
I really want to get the Yamaha going.
Waiting for some good not hot and humid weather to get out to the shop.
Larry