Any popular aftermarket carbs fit my 81 xs400?

Hi there, Names Christian and I'm more then new into the two wheel world and its my first post on here. Bought my first bike about 3 weeks ago. Been a mopar technician for about 5 years. This question in the car aspect would be silly obvious and im hoping its not for bikes too. But if I wanted to go with something impressive on my car id throw a Holley 4 barrel at it and be good to go. Are there any popular aftermarket carbs that bolt on to an 81 xs400? Nothing really wrong with mine on there now but I'm just thinking anything more fuel efficient, maybe some power I'm not sure asking around.

Thanks for your input, much love

Welcome to the forum! I'm new to old bikes so I am not much help. Sorry.

I think any popular aftermarket carb would do the trick provided you secure it with an airtight boot that fits both the carb and the engine, and tune the carb correctly.

I think people here mostly avoid fitting aftermarket carbs because the cost of the carbs is nearly the same cost of the bike lol

If your carbs work, the usual thing we do here is swap out the air boxes and replace with pod filters or foam filters, and then re-jet the carbs to allow for a bit more power, and fit a new exhaust to allow more flow.

If you really want new carbs, check out the Mikuni VM34 round slide carbs maybe?

Recreateme said:

I think people here mostly avoid fitting aftermarket carbs because the cost of the carbs is nearly the same cost of the bike lol

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Bingo.

A few people do invest quite a lot, but it is more commonly for a restoration. There are a few fairly expensive custom builds on here, however. Still, I have yet to see much emphasis on actual measurable performance. I have seen a single carb conversion and there is a guy out there somewhere with a turbo SOHC.

I believe I read on here that someone tried using these and was suscessful in getting to work.
Keihin carburetors,they are on mikesxs.He had down size the jetting a lot in order to get the engine running properly.

I noticed Mikesxs has replacement aftermarkets under the 650 section but it replaced a BS34 which is what is the the 400 as well. I assume that would work.

http://www.mikesxs.net/product/48-9000.html

That's a nice setup and with longer carb mounts they would probably help disspate fuel very well.I didn't read the specs but I assume they are jetting for the pod filters already?I also assuming they would probably work but with major main jet and adjustments of the slide needles.It would be a trial and error experiment basically.Is somebody can design a single manifold that works with one carb Im sure with a little effort you could adapt these carbs onto out bike with significant performance gains.Once again they quite pricy but go for it if the money factor isn't a problem.Adapting these carbs asumming they fit and boilt on with the manifolds jetting would be all you would have to figure out.

rugbywarrior89 said:

I noticed Mikesxs has replacement aftermarkets under the 650 section but it replaced a BS34 which is what is the the 400 as well. I assume that would work.

http://www.mikesxs.net/product/48-9000.html

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Avoid those carbs A lot of 650 guy have had a lot of problems with them and are a bitch to tune. I don't know of any 400 guys using them and for the price I would not want to find out if they don't work

If I had another project bike I would experiment with them IF I could afford them.

Thanks abunch everyone! got the bike running today so I can take my time finding a good carb to swap with and still ride in the meantime

Recreate:Mikuni VM34 round slide carbs maybe

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.I also have heard of people using these but maybe they didn't know what they were doing.The problems they had was they couldn't get them to lean out even after making jetting changes.They work better on the xs650 than on the xs400.I don't have any problems with my stock bs34`s so I would experiment by changing carbs on my bike.You know the saying if isn't broke don't fix it.This why I want another project bike.Thats not in my forseable future at this time.

So I have a 79 XS400 that I have Emgo pods on the stock BS34's and high flow mufflers. Come to find out that the carbs are swamp things as the bike hadn't been on the road since 1993. I am finding that it might be more cost effective to pick up a set of VM30's or VM34's instead of completely overhauling the stock carbs. The quote I have to overhaul the BS34's is in excess of $500, whereas I can pick up VM30's or VM34's for under $300...What should I do?

BTW, the bike runs fine at idle, but under load, ie riding it, it pops through the left carb, which I am confident is a lean condition. That's why I went to have the carbs re-jetted.

Who on earth is quoting you $500 to rebuild a pair of BS34s? You can buy all the parts needed for a complete rebuild for under $100; just disassemble them, soak them in vinegar, boil them for a while, and reassemble.

Apparently that's getting them cleaned, re-jetted, synced, and dialed in back on the bike. I paid $300 almost 5 years ago to have the carbs on an old CBR I had just to have them cleaned and synced. This is why my daily is fuel injected...

I had vm30s on my xs400. They worked okay but it left me wishing for more throttle response. I got the vm26 kit from speedmotoco and have been very happy with it ever since, although I did have to play with jetting as its not fully bolt on. Throttle response is as fast as I can whip the throttle and the top end is good enough for me as I'm not on fast roads very much.

If you go the VM route know this. VMs are very finicky since they are cable operated. While they work, I am not a fan of the 2 into 1 throttle cables as they leave a lot of variables to mess up your sync. Syncing the carbs, making sure float level is correct, air mix screw adjustments are all very important as to how the carb performs at different RPMs. As do the Main Jet, Pilot Jet, and needles but they are easier to set up and adjust. The sudco tuning manual and catalog will help you out understanding these carbs.

Also if you go with VMs and how much room you have I highly recommend getting the 90 degree elbows that go ontop of the carb for the throttle cables. These will help with binding and make syncing easier.

At the end of the day the xs400 does not have much aftermarket support and if your wanting to have fun building something up go for the xs650, cb550/750, or even the sr500 has more support than the xs400.

The only reason I spend gobs of money on my 400 is that it was my first bike and Ive already got too much in it for what I would ever be able to get out of it.