Aftermarket carbs for xs400

[TimBuz]

Hey guys, I've got a 79 xs400, I've taken it back to frame and started piecing it back together, tidying the wiring etc making a sort of brat cafe kind of thing, heres my build thread: http://www.dotheton.com/forum/index.php?topic=60861.0

Anyway, I ordered some Mikuni Vm30's from partzilla a while ago but they have repeatedly pushed back my order and given me excuses as to why they cant get them in. Recently been told they wont be able to get them from mikuni at all. I was wondering what are my other options for aftermarket carbs? Possibly TM28's? Or would persevering and trying to find VM30's from another vendor be my best option? My stock carbs are not worth persevering with as a lot of bolts have been stripped and loctited in by previous owner, choke index ball bearings are missing, a bunch of seals are missing throttle shaft seals need replacing and screws holding the butterflies are also stuck and stripping.

 

[SUBT3RRA]

I have a 1980 xs400 with stock carbs (Mikuni bs34's I believe). I had a stripped idle screw and did a bunch of research on new carbs thinking I wouldn't be able to get it out. Every one I talked to said changing carbs was going to be a hassle. They said I'd be better off finding a set of good used ones and rebuilding them. They are very good carbs and really shouldn't be a problem if they are maintained. I figured if I'm that stuck I may as well try to fix what I have. If it works then awesome and I save some $. If not I get different ones anyway.

I was able to fix mine so I got lucky. Point is what have you got to lose? You may be able to fix the ones you have, maybe not. I just recall sizing the carbs to VM's seemed like a PITA and everything I found said B'S is a better carb anyway. No one made me feel confident it wouldn't be trouble. My 2 cents and good luck man!

 

[TimBuz]

Cheers for the input yeah Ive weighed up my options and have got it going with the stock carbs but after ive stripped these screws and one of the housing cracked from trying to drill them out i'd rather start over with VM30's. Plus theyll give me more clearance to hide my lithium battery under the rear tank mount anyway. I've found this jetting guide for a kz400 that seems like it should get me in the ball park, its richer than what they use on cb350s/60s and leaner than what ive seen used on kz440s and cb450s so should be a good starting point

Factory jetted Mikuni VM30-83 400cc
**change supplied main from 250 to 230
**change pilot from 40 to 27.5
**change throttle valve cutaway (slide) from 2.5 to 3.0 if bogging
*Jet Needle : 6F5 on #4 (1clip richer)
keep needle jet stock P-5
Keep air jet 2.0

 

[SUBT3RRA]

Sounds like a plan - I'm looking forward to updates, and again good luck! I jetted my carbs after new pipes (I called it jet roulette!), so I feel for you and the time it takes to get it right... but you'll get it...

 

[xb33bsa]

30's are a bit big go with 28's, bigger is rarely better

 

[TimBuz]

People have gotten 32's to work on xs400's so I'm sure 30's will be fine with pods and free exhaust. Plus VM28's mounting spigot is 5mm less in diameter and won't fit the stock boots (I have brand new ones to use)

 

[xb33bsa]

People have gotten 32's to work on xs400's so I'm sure 30's will be fine with pods and free exhaust. Plus VM28's mounting spigot is 5mm less in diameter and won't fit the stock boots (I have brand new ones to use)

ok but 28's would be best most people assume bigger is better, they end up with something even more difficult to tune
and if you are running small pods then you are just restricting air flow you need the largest filters you can fit

 

[TimBuz]

I'm running foam uni filters, it's pretty unfeasible for me to try and keep the stock airbox. I know there is a tendency for people to over carburate that's why I went the 30's instead of 32's haha. Seen plenty of people run 30's on cb350's with little problem. Should be getting them shipped soon with a few different jet combinations so i'll post up progress in my build thread