cv34 sync question. What is actually adjusted?

I am very confused about what it is you actually are doing when you sych the carbs. I keep hearing that you want to just see a sliver of light through the carbs when done right. But what is it that I am supposed to be adjusting? am I turning the air/fuel mixture screw? am I just turning the Idle adjustment screw to set the idle? I dont really know what I am supposed to be looking for. Everything else was way out of whack on these carbs so Im sure this is not right either. thanks

Your adjusting the "butterflys" (Throttle) of each carb individually. Your matching each cylinders idle.

You want to adjust the three small, flat head screws located between each carb. They are held on by a 10mm nut that you need to loosen in order to adjust the screws. Each screw adjusts the carbs to its right and left.

I never bench synced mine, but I vacuum synced them while running by using a homemade manometer consisting of a clear tube attached to a wooden dowel and some 10w oil. YouTube has a bunch of videos on making and using these things. I made mine for under $5 and my bike is running great throughout the range and all spark plugs look identical.

Carbs need to be synced occasionally because of the wear of cylinder rings, valve seats, and any other part that controls sealing in the cylinder. Basically what you are doing is ensuring that each cylinder is creating the same amount of vacuum. You do this by restricting the amount of air that is allowed into the cylinder using the butterfly valve in CVK and BS carbs or roundslides in VM carbs. Close one more compared to the other three and it will pull higher vacuum.

When you are bench syncing you are just setting the carbs so that each one has the same amount of opening. Its a great place to start but you still need to bench sync them once they are on the bike if you want it to run really nice.

To sync the carbs you have to know what kind of carbs you have. If they are VM then there is a screw and lock nut on top of each slide, under the cap. You can lift each slide individually using this setscrew. Lifting or lowering each individually will change how much vacuum it will pull.

If you have CVK or BS type carbs then you will use the three set screws one between each set of carbs. in this case the screw closes one carb and opens its partner at the same time. The order in which you should adjust the screws is:

1-2 screw
Blip throttle and then adjust idle speed.
3-4 screw
Blip throttle and adjust idle speed.
2-3 screw
Blip throttle and adjust idle speed.

Sorry if this is all very patronizing but I thought it would help to break it down just to see if I could remember it all and just in case anyone had questions they didn't want to ask. Good luck and have fun.

so what am I looking at? what will be moving up and down? is it the butterfly on the engine side of the carb or is it the brass colored slide in the middle of the carb. if I open the choke up all the way to look through the carbs and oven up the throttle all the way the slides are all up like half an inch and I can see a tube that looks like it goes up in the middle of it. Is this what I am adjusting? If so it sounds like they are open way too far. If it is the throttle butterflies that I am adjusting, cant I just do that with the main plastic screw adjuster in the middle of the 2 and 3 carbs. Sorry for all the dumb questions but I just want to make sure they are adjusted correctly. Thanks for all your help. If anyone has any pics that would help me out. I have Kehin CV34's by the way.

kzbobber1 wrote:

so what am I looking at? what will be moving up and down? is it the butterfly on the engine side of the carb or is it the brass colored slide in the middle of the carb. if I open the choke up all the way to look through the carbs and oven up the throttle all the way the slides are all up like half an inch and I can see a tube that looks like it goes up in the middle of it. Is this what I am adjusting? If so it sounds like they are open way too far. If it is the throttle butterflies that I am adjusting, cant I just do that with the main plastic screw adjuster in the middle of the 2 and 3 carbs. Sorry for all the dumb questions but I just want to make sure they are adjusted correctly. Thanks for all your help. If anyone has any pics that would help me out. I have Kehin CV34's by the way.

I don't have at hand a link for comprehensive info and pics directed specifically at Kehin CV34 carbs, or any Kehin CV carbs.

However, many CV carb principles are the same, regardless of bike brand or carb brand.

Check out these links for some helpful info and pics about what goes on inside CV carbs:

www.drpiston.com/Cvcarbs.html

www.thegsresources.com/gs_carbrebuild.htm

Good Fortune!

Here's some more info from Dan's:

Link to Japanese carb section
www.dansmc.com/carbs/Japanese_Carbs/Carb_pics.htm

from Dan's Motorcycle Repair Course
www.dansmc.com/mc_repaircourse.htm

Good Fortune!

Dessert

kzrider.com/index.php?option=com_docman&...d&gid=475&Itemid=108

Good Fortune!

thanks for the info guys. I am still a little confused though. I know how to adjust the float levels, I know how to adjust the idle air mixture screw, but I guess I am not understanding how and what I am adjusting when syncing the carbs. is there a bolt somewhere that is turned or a screw? and if so what is it moving? Im sorry, I just dont know alot about carbs. i have learned alot in doing this but just need someone to spell it out for me in lamens terms. thank you

ok so I think I got it figured out. syncing the carbs is just making sure that all the butterflies are opening exactly the same amount at the same time right? At least that is what I gathered from all the reading I have done. thanks for all your help.