What are GOOD aftermarket carbs for a 1977-1978 KZ650?

I got this bike from my uncle. its in great shape and I want to make some changes, specifically the carbs. To be honest, cylinders 1 and 3 keep turning up black plugs no matter what, even after my uncle had the top end rebuilt. There are VM24ss on the bike now, stock with airbox. I was thinking these ate they too big, going from 24 to 29? :

 

What about cleaning and tuning the vm24's first?  

A friend wants to buy the Vm24ss. I want new carbs, a clean slate. As a grad student, I dont have a lot of time for working on the bike. i wish I did!

Most aftermarket carbs are too big for a 650.  Some of the best are RS34's, but they list the 750 as the smallest recommended application.  That said, I'm sure there are people that have done it.

One option is a properly rebuilt set of VM26's.  I'm selling a set, rebuilt by member Clay.  He's super knowledgeable and doesn't put out junk.

www.kzrider.com/forum/23-for-sale/621309...rbs-rebuilt-restored

AlexRocco post=911928 userid=81705A friend wants to buy the Vm24ss. I want new carbs, a clean slate. As a grad student, I dont have a lot of time for working on the bike. i wish I did!

Switching to a set of aftermarket carbs would be both the most time consuming path you could take, while at the same time being the most expensive.

Aftermarket carbs are not plug and play.  They require extensive tuning and testing, along with a lot of previous knowledge and experience with carb tuning, to get to the point where you have a good running bike.

The most time efficient path you could take would be to restore the bike to stock.  Thoroughly cleaned stock carbs with stock settings along with the stock airbox and filter.  

If you want to save time, find someone experienced to clean the carbs for you.  If you ask Nessism he might be willing to rebuild you set for you.  He's rebuilt many sets and does fantastic work. 

If you go that route you would save a huge amount of time, and it would only cost 1/4 to 1/3 of a new set of CR carbs, and it should be plug and play.

DO NOT change the carbs from stock. Especially don't go bigger than the stock 24's.
Of all the Z range, 650's are already have the biggest carbs versus capacity. 
Z650
Vm24 dia = 452mm sq x 4 = 1808mm sq div by 652cc = 2.77mm sq per cc.
Z900 (a4)
 Vm26 dia = 531mm sq x 4 = 2124mm sq div by 902cc = 2.35mm sq per cc.
Z1000
Vm26 dia = 531mm sq x 4 = 2124mm sq div by 1015 = 2.09mm sq per cc.

The quickest and most cost effective way to go is to use the stock carbs. Kawasaki have already done all the development work that you would need to do again by swopping in a different carb set. 
There are several reasons plugs can go black as I previously posted. 

 

Ditto everyone's thoughts on this, KEEP what you already have! You reference "starting with a clean slate". Oh YES you'll be starting with clean looking-at stuff but you'll be opening a can of worms i doubt you'll be prepared to tackle. As Warren laid-out the perimeters for you. Take heed of them numbers!! Bigger means less intake pulse especially at lower RPM's. Meaning a good chance of wrecking the crisp rideability the smaller venturi original carbs provide. Save the money for flash and invest now to start paying those student loans off, ha. Or think how many frozen pizza's and ramen noodles you could buy, college isn't cheap!   

There are not a lot of options for replacing your existing carbs.  The VM24's are well matched to the 650 engine.  You sound like someone who doesn't understand the purpose of carbs on an engine.  They are far more than just a fuel delivery mechanism.  They deliver fuel AND air in a mixture that is suitable for the cylinder across a wide range of rpm's.  And there are FOUR of them operating independently of each other.  Unless you're an engineer with experience on combustion engines you are asking for a pile of trouble by switching to something else.  But....

If you decide to go against the advice of many highly experienced motorcycle engine experts....don't sell your VM24's.  You will eventually realize the error of your ways and will need them to get your bike running again.

hardrockminer wrote:

There are not a lot of options for replacing your existing carbs.  The VM24's are well matched to the 650 engine.  You sound like someone who doesn't understand the purpose of carbs on an engine.  They are far more than just a fuel delivery mechanism.  They deliver fuel AND air in a mixture that is suitable for the cylinder across a wide range of rpm's.  And there are FOUR of them operating independently of each other.  Unless you're an engineer with experience on combustion engines you are asking for a pile of trouble by switching to something else.  But....

If you decide to go against the advice of many highly experienced motorcycle engine experts....don't sell your VM24's.  You will eventually realize the error of your ways and will need them to get your bike running again.

 

I respect the wisdom and experience of all of you, so, the carbs will stay. I'll have them checked out to see whats wrong. Thanks to you all for your guidance.

More monies for a Quad Party..used to attend concerts at the KU Campus, ha.

Just my 2 cents, but I would contact Nessism or asphalt900 to discuss having your carbs renewed by an expert. 

sf4t7 wrote:

Just my 2 cents, but I would contact Nessism or asphalt900 to discuss having your carbs renewed by an expert. 
 

I cant afford it right now, with school and all, but an old-timer friend of my uncle's who lives in another state  made a good living building UJM engines, normal and racing, said he can pop by when he visits my uncle in 10 days, take them out, take them home with him and do what needs doing.

One thing I left out, when in the garage, the bike fell over onto its engine guards and that may have messed up the carbs. My uncle said this happened Feb 2024.