Keihin CV34 to Mikuni BS34 More air restriction???

steell wrote:

Yet you may well be the Internet's greatest advocate for running BS34 carbs

Um, no, that would be WiredGeorge

But George only advocates them for near stock bikes, not big cc monsters.

:laugh:

bsjoker101 wrote:

I am no advocate for any carb either just trying to get my old junker running.
I'm happy with my larger pilots.. Runs fine on that circuit. I think I need to shim up the needles a bit for more gas at high rpm's does this sound like a resonable guess? Ah hell why even ask for $5 In shims I'm trying it anyways..

If it's a 6K stumble, the problem generally is the slide is not lifting quick enough.

Best solution if the shims don't cure it.....get a jet kit and install it as a stage 1 with the airbox....

larrycavan wrote:

If it's a 6K stumble, the problem generally is the slide is not lifting quick enough.

Best solution if the shims don't cure it.....get a jet kit and install it as a stage 1 with the airbox....

This is good advise, and glad I could help

It will either be the needle like your guessing or this.
Changing the needle height might just move the stumble. In that case a jet kit with slide adjustment will make a big difference and a new place to start tuning from for your setup.

When it pops as you snap the throttle closed from high rpm, its returning to the idle circuit, and there is too much air present. Therefore, you can adjust this by adding more fuel to this circuit via your mixture/air screws. Try an extra 1/4 turn and ride again...

GL!

So whats the problem with the BS 34s? Do they not perform well,are they hard to tune or what.Seems to me if Maw Kaw put them on the bike(s),there was a reason for it.I dont have a big fire breathing monster,but the bike sure aint stock-it has BS34s and they do their job.I have watched posts over and over here about re-jetting,adjusting this,tweaking that-- methinks sometimes we fiddle-fart Way too much and ride Way too little.If the damn things are running,fire them muthas up and ridem until something major breaks and quit screwing with the damn things.Jeez.bj

hocbj23 wrote:

So whats the problem with the BS 34s? Do they not perform well,are they hard to tune or what.Seems to me if Maw Kaw put them on the bike(s),there was a reason for it.I dont have a big fire breathing monster,but the bike sure aint stock-it has BS34s and they do their job.I have watched posts over and over here about re-jetting,adjusting this,tweaking that-- methinks sometimes we fiddle-fart Way too much and ride Way too little.If the damn things are running,fire them muthas up and ridem until something major breaks and quit screwing with the damn things.Jeez.bj

hocbj23 wrote:

If the damn things are running,fire them muthas up and ridem until something major breaks and quit screwing with the damn things.Jeez.bj

X2 :woohoo:

BJ

Here's the problem with the BS34's.

On a mild motor, they're fine. Now toss in some performance cams to the mix and they can be pain in the arse to dial out the stumble unless you spring for a jet kit.

So...let's look at the scenarios I've seen play out time and time again on this site.

A guy buys a rack of those beauties for say $100. Then he ships them off to some rebuilder and dumps a few hundred more in them....ONLY to get them back and have to dink around with them for weeks....

Same thing with laying down $500 for a rack of used 29mm Mikuni Smoothbores and then having to rejet them and if you're lucky, there's no stripped out jet blocks...

So call me crazy but isn't it a whole lot better move to put a brand new set of REAL performance carbs on the bike from the beginning for a little more money? They're new, they won't have stripped out holes...

If you do really want BS34's on a bike with cams, porting, bigger pistons..... then the quickest way to making them work is a K&N or DynoJet jet kit with new needles.

Even with a jet kit, I've seen situations where adding cams can require a custom needle to make them carburete properly through the entire rev range.

All said and done, buy the BS34's,send them out for overhaul, buy the jet kit, go through the work and you still don't have the acceleration performance of a good rack of CRS, FCR, or RS manual throttle slide carburetors..... BUT you've got dam near the same money tied up...... :huh:

There are applications where the BS34's are fine and there are applications where they just don't make a bit of sense

As you increase the performance output of the engine, the carburetors should be upgraded to something that not only feeds it the air it wants but more importantly will deliver the fuel curve it needs....

Well I can add my 2 cents, stock bike @ stock carb, designed to work together. Leave that real very far and you will be tuning, and possibly gone far enough where they just won't be right ever. So once you lower your low speed vacuum signal with the cams and pods, why would you even bother with CV carbs? Still trying to putz around and have low emissions? No that's why the build up, right? Nothing like a performance carb for the application.
So being more of a car guy I have got to say I LOVE Weber carburetors, and on a Worked V8 a Holley Double pumper!