Aftermarket Carbs

SoraXS400

SoraXS400

1982 XS400
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Location
Michigan, US
Looking to upgrade exhausts and I was wondering if these carbs would work well with our bikes and if anyone has used them in the bikes? These are supposed to be performance carbs, what's the difference and is it any better than the stock carbs with a new exhaust?
 
Read around here and you'll find that a few people say they are worthless....i'm just reporting what i've read.
If it were me....genuine mikuni VM-28 would be the way to go.
I've personally tossed a multitude of ideas around for my build...VMs...microsquirt...etc.
But there is really so much you can get out of these little 400s IMO...and the performance gains are not commensurate with the money spent.
A good tuning and maintenance on these and they will run great and perform well enough with stock carbs.
Not trying to tell you what to do here just giving my humble opinion.
 
I was just looking for a little more power out of the bike and I figured with a new exhaust system, those carbs would be better since they don't have the vacuum operated secondaries and whatnot. Our bikes run better gravity fed than with the vacuum so I figured I'd find something else easier to work with and better performance. Not willing to spend the $360 if they don't work better at all, though.
 
SoraXS400 said:
I was just looking for a little more power out of the bike and I figured with a new exhaust system, those carbs would be better since they don't have the vacuum operated secondaries and whatnot. Our bikes run better gravity fed than with the vacuum so I figured I'd find something else easier to work with and better performance. Not willing to spend the $360 if they don't work better at all, though.
Click to expand...

Looking for the same idea so I'm curious on what you will came up with. We are gonna start checking on the 1981 XS400 right after we finished installing the new wheels and Toyo tires on the current truck project. I've read couple of mixed reviews with MikesXS carbs.
 
Dringed02 said:
Looking for the same idea so I'm curious on what you will came up with. We are gonna start checking on the 1981 XS400 right after we finished installing the new wheels and Toyo tires on the current truck project. I've read couple of mixed reviews with MikesXS carbs.
Click to expand...
I'm moving states here pretty soon so I won't be able to work on the bike for the next few weeks, however I may just end up buying a jetting kit and building my own exhaust, it seems that every time anyone tries to ask a question about the carbs or performance the immediate response is "keep it stock". Really starting to piss me off.
 
Don't get pissed because you don't like the answers you're getting....this is a forum and as such people will give their opinions.
With mods, it is always a trade-off thing...I am pretty sure you can get some performance increase but at the cost of many....many hours and money spent tuning.
You can bore the cylinders,get forged pistons, get a lightened crank and race cams made, put on flatslides hell you can even put EFI and a turbo or supercharger on there.
Don't get me(...us) wrong, I would LOVE and follow avidly a thread that would go balls to the wall of this engine but reality is...do you really want to spend 5-8...10K even to get a 5-10...bhp gain?
Most threads here or on other forums that try these mods go silent after while, either from lack of money,will or patience from the builders...
Guys on here like xschris or 16VGTIDave have been tuning/ wrenching on these bikes for a while, know what they are talking about and can help....
Anyway, like I said I would follow such a thread...
Still sticking with my first opinion on this...if you'really going to invest $$$$ get genuine VM-28 carbs.
Best of luck on this...and the move.
 
Its not a "you ask we tell" situation. Your opinion doesn't change if I want a new exhaust on my bike, I don't care that the carbs need tuning, hell, my little wr250f needed to be rejet with just the baffle removed. I understand how these bikes work, and I've asked how things perform and I get "keep it stock" with no explanation. This isn't just a "Help my head gasket is leaking" forum, its for a collection of riders with the xs400 and that's where the problem starts, with people like you who buy 5 xs's and keep them all stock and tell other people to keep it stock, just because "ohh it runs better stock" when they asked a question about changing exhausts. If someone asks a question and you immediately say "keep it stock" with no other help, get off this forum.

I understand that you think you're some mechanic or something, but I've also been working on bikes since I was little and I understand how engines and carbs work. I asked if anyone has used those performance carbs because they don't use vacuum operated secondaries and look to be easier to tune, therefore I was getting some confirmation.
 
You asked about if these carbs work well. We said NO. You asked if a "new" or I would guess after market or even home made exhaust would be "better" we said NO. I have done the after market exhausts the five different styles of pods ( on the carbs and with stock stacks). I have run xs360 carbs 77-79 xs400 carbs and 80-82 xs400 carbs. So I know what works the best overall. Keeping it stock works the best. Others on this forum have done those carbs as well as xs650 guys which I have had those bikes also and they say they suck. I talk to Yamaha mechanics that have worked on these bike when they where new and get the same response. I have had bikes for over 30yrs. When you tell me that you removed the baffle out of a bike says a lot about what kind of " mechanic" you are. If you think drilling hole in muffler or cutting them off to "make more power" is a good idea then your wrong. Put one on a dyno and see for yourself what it does to the bike. Louder don't mean more power. I have sohc xs400 bikes not the dohc ones. Dave has one that he has spent tons of miles on. But if your the one with all the answers show us how it's done. This is all I will say about this, have a good day sir.
 
xschris said:
You asked about if these carbs work well. We said NO. You asked if a "new" or I would guess after market or even home made exhaust would be "better" we said NO. I have done the after market exhausts the five different styles of pods ( on the carbs and with stock stacks). I have run xs360 carbs 77-79 xs400 carbs and 80-82 xs400 carbs. So I know what works the best overall. Keeping it stock works the best. Others on this forum have done those carbs as well as xs650 guys which I have had those bikes also and they say they suck. I talk to Yamaha mechanics that have worked on these bike when they where new and get the same response. I have had bikes for over 30yrs. When you tell me that you removed the baffle out of a bike says a lot about what kind of " mechanic" you are. If you think drilling hole in muffler or cutting them off to "make more power" is a good idea then your wrong. Put one on a dyno and see for yourself what it does to the bike. Louder don't mean more power. I have sohc xs400 bikes not the dohc ones. Dave has one that he has spent tons of miles on. But if your the one with all the answers show us how it's done. This is all I will say about this, have a good day sir.
Click to expand...

I've worked on all my bikes too, I've taken them to dynos. My wr250f rejetted without a baffle makes more torque, and slightly more hp. I made an example that making any adjustment requires rejetting. If you say that they're trash with no explanation, it makes you sound like an amateur who doesn't tune correctly. Almost any carb can be tuned with aftermarket parts, jetting is key. You didn't address any explanation to why they were bad. These vacuum secondaries are trash for these bikes, they are the cause of 90% of the carb problems with pilot jets.
 
Those carbs have been discussed before, multiple times. The information is already on the forum. It can seem awfully pointless to type out long-winded replies when it's just rephrasing old information.

It can be a great help to read older threads for insight. A lot of applicable information can also be found on the XS650 forum, especially for MikesXS parts.

Those carbs are known to be poor quality but a set of genuine VMs could work well if the owner has the knowledge, willingness, and patience to tune.
It's a privilege to be able to follow a build thread with a knowledgeable owner properly tuning aftermarket carbs, but so many ambitious threads go silent after some time.
 
Like I said....if you go through with it...I want to see the thread...
Best of luck.
Not beiing dicks here just giving our two cents.
 

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