Carb Boring

I've always wondered if this could be done and I was thinking about doing it to a set of VM24's just because I have a couple extra sets lying around. It seems like it would work to punch them out to 26mm or so instead of buying a new set.

Anyway this guy is obviously doing it for a price. I'd never pay him to do mine but it means someone else is doing it meaning maybe there is some information out there??

Has anyone done this?? Heard of this??

cgi.ebay.com/ebaymotors/Kawasaki-carbure...fPartsQ5fAccessories

It makes no sense to do a set of 24s. It costs $250 to do it and you can buy a set of 26s or 28s on eBay for around a hundred or so.

Sorry I wasn't being clear. I'd just do it my self and I'd use 24's because I have a bunch of extras. I was just wondering if anyone had any reasons it won't work or if you've done it maybe someone has tips.

I sold a set of 28s bored to 29mm. No idea if they work.

From what I've personally flow tested and from my years of working on KZ's.

1 - carbs need to be synchronized on the engine they will be run on to have them correct. Cylinder variances can affect the amount of vacuum they draw.

To simply make them all equal settings on the flowbench or with a drill bit is certainly better than nothing but it does not assure they will make your engine yield the same amount of vacuum on every cylinder.

That's why carb synch is the last thing done for a tune up. Valves and ignition timing are always precursor to carb synch.


Last time I tested a 26 it flowed 74CFM with an airbox stack horn on it BUT that was at 10" not 12". It was on a little Superflow 110 bench also. Nobody I know uses 12" as a standard for flow numbers.

With that stated converting 70@12 to 10" drops them to 63.9 CFM. That's still about 5 CFM more than the head flows stock.

The manifold you use will affect the flowbench numbers.

As for calibrated to work correctly right out of the box......seems like I've heard that somewhere before

I think Otto has the right idea....put a rack of 26's on and be done with it.

So how about a set of 26's to flow more for a hopped up 900/1000?

Larry - how do you go about matching, when discussing CFM, between the carbs and the head/cams/valves?

I'm actually going to put a set of vm 28's on my 650 project bike. It's just always been one of those interesting ideas that I've wondered about.

Alot of the claims he makes lets me know he is seriously exagerating but who knows maybe it would work for a quick and easy do it yourself horsepower increase when added to a pipe and better air filter. I think I'll probably try it someday just to see what happens. I was just wondering if anyone else had tried it.

so you now bored the carbs 2 mm larger. cool right?
what about the slides?
you now have 1 mm on each side of them.
see the problem here?

I thought about that but the slides are indented into the sides of the carbs at least 2 mm. they would still be able to keep a seal around the outside.

Becker wrote:

I'm actually going to put a set of vm 28's on my 650 project bike. It's just always been one of those interesting ideas that I've wondered about.

Alot of the claims he makes lets me know he is seriously exagerating but who knows maybe it would work for a quick and easy do it yourself horsepower increase when added to a pipe and better air filter. I think I'll probably try it someday just to see what happens. I was just wondering if anyone else had tried it.

Keep in mind that bigger carburetors flow more air than smaller carbs BUT between two carbs of equal size, the one that delivers the better mixture curve is the one to have.

I've never tried or known anyone who's had his carb boring done before. He's been around since back in the 80's so his carbs might work well. I honestly can't comment on their function quality. I can only relay flow numbers I know to be valid.

Never in a million years would I claim to have modified carb come ready to bolt oh and ride away without the possible need for further jetting. That's quite a claim to backup.

It's just like rebuilding CV carbs and inferring they are ready to bolt on. OK...fine if it's a stock motor with stock airbox. Throw cams into the picture or other engine mods......WHEW! I just can't see it.

Only way to go for that is tell the customer up front that you're installing a jet kit at the baseline settings and fine tuning may be required.

I've never had a jet kit not work with baseline settings. That is to say the bike should start right up and be ridable. But outside of that.....it's a crap shoot.

DoubleDub wrote:

So how about a set of 26's to flow more for a hopped up 900/1000?

Larry - how do you go about matching, when discussing CFM, between the carbs and the head/cams/valves?

Depends on the intended use of the motor and which carbs they are.

In general, for a drag racing motor, it's common to have the carb bore equal to or slightly larger than the intake valve size.

In general, for a drag racing motor, it's common to have the carb bore equal to or slightly larger than the intake valve size.

I didn't know that. Interesting.

I'm guessing that he does his best to guess and then the customer puts them on and it works so they ride it. Obviously not for serious bikes.

that being said I think I might try to do it anyway. Someday.