1982 XS400J Maxim Carburator Intake Boots (Compatibility?)

[sammermpc]

I recently acquired what I believe is an XS400J Maxim. I think this is one of the DOHC models? At any rate, it idles very fast and one of the pipes runs superhot, so I'm guessing there is something wrong the the carbs.

One of my intake boots is cracked and it looks like PO tried to repair it at some point. I'd like to replace it.

I'm pretty confused about the different XS400 models though, and parts compatibility? I'm guessing I can't use any of the SOHC carbs on my Maxim? Can I confirm what specific model I have definitively?

I don't see much in the way of boots — but there are a number of boots for sale (in four packs) for the Yamaha Seca? Would those work?

At any rate, I appreciate any general pointers about part sourcing (OEM part-number list?) that you can help me with!

 

[Lou Ranger]

Welcome to the Forum.
If you have a Maxim 400 then the Seca 400 stuff should work. It's the transmissions that are different, but the engines are the same.
If you post a picture we can confirm for you.

It seems to me that some individual sohc carbs might be the same, however, I am not sure that the set of carbs from a sohc could transfer to the dohc. I think the apparatus which links them together is different. Not sure though so wait for someone else will confirm before you spend any money on the wrong thing.

Have you tried the carb cleaner spray test to confirm a leak in the intake boot? Again, worth doing to ensure you actually do need new ones before buying any.

 

[xschris]

Sohc boots are NOT the same as the dohc ones.

 

[sammermpc]

OK — yeah, and I've figured out I definitely got the DOHC XS400J Maxim. So it seems like most of the commonly available XS400 boots on Ebay and the like won't work.

It also sounds like its a real chore to pull the carbs at all! I've seen some posts where people talk about dropping the motor to do the job right!

So quickly, then — if none of the SOHC boots are compatible, and DOHC Maxim boots are unavailable (as far as I can see) — what are my options? There are boots available for the XJ650 Seca (in packs of four) — would those fit?

There also look like there may be some options out there if I search more broadly for BS34 Mikuni carb boots. Can I confirm that those are the ones I've got?

Yikes, seems like this particular year/model are a bit of a headache...

 

[Lou Ranger]

There are 2 ways to look at it.
The dohc is a bit or a headache, or, the reason there are so few used parts around is that the dohc is virtually unbreakable.

Have you confirmed with the spray test that the boot's crack goes all the way through and is, in fact, leaking? You could get lucky and find that the PO mounted them incorrectly and they aren't sealed there. My dohc boots had lots of surface cracking but were intact, sealed and worked perfectly.

If you have a close picture of the installation and, the PO's "repair", maybe we can help figure out a way to do a repair until a set of intact boots comes up on e-bay.

 

[sammermpc]

Ok, I actually did do the spray-test with WD-40, but I didn't notice anything. I didn't do it that carefully or systematically though.

I do think I need to pull the carbs to clean them, and I was figuring I'd just replace the boots then to be safe, anyhow, but it's true, I have not verified if they're leaking definitively.

One cylinder is definitely running much hotter than the other, though, and the plugs seem OK. The idle is consistently around 4k, and it doesn't drop down quickly when you pull the throttle. From what I've read, this seems like a classic lean condition, correct?

I will post photos when I take some better ones this evening.

 

[JaredK]

Sounds like it could be carbs out of sync, or one of them is blocked. It would be a good idea to clean the carbs first. It's not too bad - I can get mine off and stripped down in 45 minutes now. This should help:
http://www.xs400.com/forum/showpost.php?p=141089&postcount=9

Make sure you balance the carbs after cleaning them. There are a bunch of threads on this site on how to make a cheap and easy manometer.

You might also want to check the valves, which is a bit more work from what I've heard (I haven't done it yet on mine).
http://www.xs400.com/forum/showpost.php?p=104490&postcount=7

Can't remember if you do the valves before or after balancing carbs...

 

[sammermpc]

Thanks for all of the help! I did check for vacuum leaks, spraying some WD-40 around the boots, and there definitely was one going on.

Also, I did successfully pull the carbs and they're mostly disassembled now! It wasn't bad at all. Many thanks for those really useful links, Jared.

Anyhow — my question now, is how can I tell if I can re-use my boots or not? One seems OK. The other is pretty banged up. Seems like a PO tried to do a repair, but it's worsened in time. Actually, looking at them more, I think I definitely need to replace at least one. Too bad. I will keep hunting.

At any rate, I have them mostly disassembled and will give them as good a cleaning as I can! One thing I am confused about is setting the float levels. I saw in some thread that you needed to do it on the bike in the DOHC?

 

[JaredK]

I haven't adjusted my float levels (yet), but the best instructions for the DOHC are in the manual: http://www.xs400.com/forum/showpost.php?p=46729&postcount=3

It's chapter 4 on Carbs. It says you need a "special tool" but I think you can just use fuel line that fits snugly into the carb's drain hole. The fuel line should be about 3mm below the top of the float bowl body.

Not sure about repairing the intake boots. Probably best to replace, but maybe someone else has some home remedies that will at least get you on the road until you find replacement parts.

 

[sammermpc]

OK, great. I've downloaded that but haven't taken a close look yet. Yeah, honestly, I got the bike so cheap I'd be willing to spring for new boots — but I can't even find them! Most everything is for the SOHC carbs, which I understand are different (though they look very similar).

 

[Lou Ranger]

Your second pic shows a big "O" ring which looks to me to be what actually seals the air plenum from the outside world. If so, then it might be worth trying to remove the old one and thoroughly clean the channels which it seals against on both surfaces and then try and replace it with the same diameter "O" ring but one gauge larger.

The first pic, which shows part of the inside surface, does not show that big outside crack going all the way through. However, on the chance it does, it must be possible to identify the right substance to seal that crack. Likely the PO tried jamming silicon sealer, ("GOOP" or some such into it). While that stuff works pretty well to stick to hard plastic or some metal surfaces, it might not adhere well to neoprene (which is what I assume the boot is made of. Maybe something like the adhesive used to vulcanize a rubber tire patch would perform better. Or maybe even one of the new roof sealing products (which come in aerosol form) would work - especially if you could draw the mist into the crack with vacuum.

Disclaimer: Neither of the above "ideas" has been tried or tested but, if you can't find replacement boots and the alternative is not riding, they may be worth a try.