Carb tuning questions

Hello! with my first carb rebuild coming up on my 82 kz550 c this winter, id like to know all i can about carb tuning and how it correlates with things like cold air intakes, exhaust changes, and other things done that would improve performance. I hear things like jet size, and numbers and all that which i don't have the slightest idea what they mean. Is there some website, or book or something that can lay out all the technical terms and help me understand it more? I just don't wanna walk into this job blindly. Plus my manual isn't very extensive on the whole process. Thank you!

We all appreciated that you are asking first. That will make the process much less painful and frustrating for all involved.
That being said, I am going to throw a question back at you. Why do you want to rebuild them?
If you have been riding the bike, then I'd bet all they really need are some new gaskets and orings, a careful cleaning, and a proper tuning. Maybe just the tuning.

With a properly designed exhaust system and low restriction intake, you may be able to get 3-5 more horsepower out of the engine, but they will be expensive horses. You will need to change the jetting on the carbs for that. The simplest way to go is to use a kit from Dynojet or a similar company. With all of that, you will gain a little power in the upper part of the rpm, the bike will lose a few pounds ( the factory exhaust is heavy), the bike will be much louder and you may lose a little fuel economy.
If you can find an aftermarket exhaust for the 550, you may have to lose the center stand and you may have to remove the header to get to the oil filter, depending on the design.

Your choice.

Calvin9819 wrote: Hello! with my first carb rebuild coming up on my 82 kz550 c this winter...................

Before starting on this task I suggest you clearly define what you are trying to accomplish. Do the carbs currently have a problem that you are trying to correct? Are you simply looking to find more power by somehow changing carb internals? Do they leak? In other words, are you trying to fix a problem with the carbs or do you expect to gain more power by making changes to them? Ed

in general, im trying to learn everything. I want to be able to adapt different carbs from say my fiends bikes to their needs. I've graduated as an Automotive Technician, but now im looking into powersports as well. I never thought i would have this much fun working on a motorcycle, so i want to continue. And i know carbs are a huge part of performance and tuning and ive always wanted to learn how to set up carbs, what sizes to use with what conditions, differences between sizes, etc.

Ed: Specifically for my bike, I have gas leaking from the overflow tube quite often from a couple carbs. I suspect either a bad float needle, or incorrect float height. And since i have cold airs, i want to try to get the jetting to the right size to match the upgrade. Even though i know its not much bigger than a few horsepower. The PO said he put different jets in but i'm less trusting because of everything else that was wrong with the bike when i got it (Chopped exhaust, various broken bolts never replaced, improper sealing causing high idle, improper brake hardware, adjusted the air screw based on sound of the bike, the list goes on) if i remember correctly, it has a 92 main and 32 pilot. and i think he put in a 95 main and... 35 pilot? not sure.

Texas: I want to use the stock exhaust, i'm looking for it on ebay. I'm not a fan of the aftermarket exhausts out there, call me old fashioned! Unless you'd suggest i get a higher flow exhaust?

As a qualified auto engineer you should already understand the basics of carburation but maybe not specific to mc's.
This is the best overview I've found on the net with some mc specific tips and tricks.
www.iwt.com.au/mikunicarb.htm

Regarding the carb overflow -

Fuel coming out of the overflow hose (the little hose on the bottom of the carb) is the common symptom of the 3 possible problems described below. Remember - NO SMOKING or other activities that could ignite the fuel while working on carbs!

The float valve is not sealing. This may be (and probably is) just a matter of some minor dirt in the float valve and is very simple to remedy and can be done with the carbs still on the bike. Turn off fuel; drain carb by loosening big brass screw near bottom; and remove the 4 little screws on the bottom of the carb bowl. This will enable you to remove the carb bowl. You will then see the float. If you carefully remove the float you will see a stubby little needle that mates with a brass orifice; together, these two pieces are the float valve. Assuming there is no obvious damage to the needle or seat, use a Q-tip and some carb cleaner to clean the seat of the orifice and the needle. Be careful not to bend the tang that is attached to the float. This tang is the piece that the bottom of the float valve needle rests upon, and it determines the fuel level in the bowl, so bending it will change the fuel level. With the float valve cleaned it should no longer leak. To prevent a re-occurrence a quality inline fuel filter should be installed between the fuel tank and carbs. If there was damage the needle and seat should be replaced as a set; they are available.

The brass overflow tube inside the carb bowl is damaged. When you remove the carb bowl you will see a brass tube attached inside and rising toward the top of the bowl. This is the overflow tube and it leads directly to the overflow nipple on the bottom of the carb. Normally, the fuel level within the bowl rises somewhat close to the top of this tube. If the tube becomes cracked or separates from the bottom of the carb bowl fuel will flow through it and out through the overflow hose. Checking the condition of the tube is very easy after you have removed the carb bowl from the carb. Simply hold the bowl level and fill it up near the top of the tube with water or alcohol and see if it leaks. A slight crack in the brass overflow tube can be difficult to find. You can connect a rubber tube to the overflow nipple, fill the bowl with water, put finger over the open end of the brass overflow tube and blow in the rubber end and look for bubbles. If it does the best remedy is to replace it although some folks have found creative ways to repair them.

The fuel level is set too high. This condition occurs when someone has bent the float tang as mentioned above. This condition can be checked using what is referred to as the "clear tube test." The test involves attaching one end of a clear piece of flexible tubing to the carb drain hole and holding the other end of the tube above the bowl/carb joint. When the fuel is turned on it should rise in the tube to a level 2.5 - 4.5 mm below the bowl/carb joint. If the fuel rises higher than that level it may run into the cylinders or over the upper end of the brass overflow inside the carb bowl (mentioned above) in which case it will run out the overflow hose. This condition is corrected by removing the float and gently bending the tang to raise the float valve needle position. Doing this may take several tries before achieving the desired fuel level.

Correcting each of these three conditions involves removing the carb bowl. This task can be made easier if a short screwdriver bit is used, and depending on which carb you are fixing a mirror may help you locate the screws on the bottom of the carb bowl. Also, it is not a bad idea to have a new carb bowl gasket available in case the old gasket is damaged while removing the carb bowl. Ed

Perfectly detailed and great explanation on common problems, thank you Ed!
Warren: unfortunately they never taught us how carbs worked, as it was "old technology" and we had a heavy focus on diagnostics of new engines. I've done research of my own on it, though im intereted in jetting as far as performance upgrades and what not. ill be looking into that link, thank you!

Since you are wading into motorcycle carburation for the first time, stock intake and exhaust will make life much less maddening for you, and will make your neighbors happier, too.
You say you have cold airs on the bike. Do you mean you have installed individual air filters (also known as pod filters)? If so, I hope you got high quality ones from APE or K&N. The really cheap ones are poorly designed and can block the air jets in the intake horn. I have also heard of some that constantly fall off :blink:
I would add to 650Ed's nicely detailed post that if you have overflow problems with the engine off, you also have a malfunctioning petcock (fuel valve).

They were on before i bought the bike but i believe he said they were K&N filters. and yes, individual pod filters. And i have a non-vacuum operated petcock on it right now, so unless i turn it off its always on. Which i forget to turn off too.. my bad lol.