Carb's...keep them standard or upgrade????? advice please

[Mizer]

Brains trust.......I am fixing up and Bobbing my 81 XS400.

Should I keep the original vac carbs (and rebuild) or change to something else??? size & brand recommendations.

I am not working my motor and am not looking for eye watering performance, just looking for reliability and low down grunt.

Any advice would be appreciated, I know nothing about carbs.........

 

[drewpy]

cv carbs are best for lower down grunt, but I know peeps have fitted CR carbs but the engine snaps open, but this is good for racing.

all depends how much money you have

 

[redratbike]

as a cheap conversion i looked at 2 pitbike carbs meantt for a 160cc engine thought i could adapt these as a cheap alternative ? maybe just pie in the sky all depends if i can get mine working right first

 

[lhaolpa]

I've considered that exact thing myself,as why you have to have butterfly valves and slides in the same carb.I would think any carb from a 400 4-stroke enduro or street bike would work,and would be simpler.In my opinion,the diaphrams are an accident[wearing out]waiting to happen.A fragile piece of rubber in a carb on a motorcycle is not a good thing.I will keep my eyes open for a pair of good 34mm-36mm carbs to come up on Fleabay. lha

 

[OliverB]

Diaphragms have been used in CV carbs for a long time and have proven to be reliable. If you are in doubt as to the age and condition, replace them and you will most likely never have to service them again.

 

[01ps]

As long as the BS34 is cleaned properly and a filter installed, I cannot see any reason to change them. Parts are readily available if needed. They work very well once set up. As for the diaphram, if they are not leaking now, I wouldnt worry about it.

The carbs on these bikes are not a weakness at all. If there are running problems, they can almost always be solved by CLEANING the carbs, setting the floats and replacing the float needles and orings on the idle jet. You can tune them very easily with a selection of jets and a bit of trial an error.

That said, try something else if it turns your crank. Any carb with the right size flange on the intake side should work, but you will need to tune them to fit.

I tried to fit a single vm carb this pastr winter, but while it ran, there were lots of problems I was not willing to chase down.

 

[lhaolpa]

Diaphragms have been used in CV carbs for a long time and have proven to be reliable. If you are in doubt as to the age and condition, replace them and you will most likely never have to service them again.

I've been trying to find carb kits for a while,without luck.Lots of places have kits for older bikes but '82 seca is not listed as a match,fitment wise.The diaphrams on mine were good as far as I can tell,as when holding my finger over the hole that air enters from,the slide fell very slowly.This was after exhaustive cleaning of the carbs. Air and carb cleaning fluid spurted freely through every orifice in the carbs.I have been riding and wrenching on motorcycles,cars tractors,lawnmowers,weedeaters,etc.since the early '60s and am aware that there have been this type carbs in bikes before,but that argument applies to many things,but does not mean that everyone has to accept that there is nothing better.I once built a Volkswagen bug with 4 Mikuni carbs setup on a rail,and after jetting,it ran like a scalded dog.It also got about 50 mpg.What I'm saying is there's always a better mousetrap out there! lha