Right cylinder exhaust is coughing/spitting

The right cylinder exhaust on my kz400 is making a coughing/spitting sound every few seconds. I have checked fuel, spark and compression, as well as messed with the air/fuel screw but nothing seems to help the problem. I know it has nothing to do with carbon build up because I just got the valves relapped by a machine shop. Is there anything else that could be causing this??

Have you cleaned the carbs by fully taking them apart and cleaning all the parts in carb dip? Replace all the O-rings? If not, it's time well spent. And don't waste money on "carb kits" because most of the time they are just full of inferior aftermarket parts.

Which carb kits are full of inferior aftermarket parts? I have been in the carb business for 13 years and understand that some carb kits coming from 3rd world countries are poor quality (such as India, etc) but the kits coming from Japan are generally coming with parts from one manufacturer who made the original OEM parts 40 years ago. I have had few inferior parts when using these kits. Which kits and parts have you had first hand experience with that have been inferior?

Most OEMs, such as Kawasaki, originally stocked enough spares for a few years. Many of the OEM parts originally branded Mikuni or Keihin are just no longer available and aftermarket parts must be used. Cleaning jets by soaking in carb dip MAY be of some use; it will certainly make them look better but the inside of the jet must be touched with a tool with serrations to remove any stuck-on stuff and that can quickly change the jet size. In addition, if a person using one of these tools isn't careful, they can alter the chamber that allows the correct fuel dispersion. I throw all used jets from any job into bins and sell them all at Christmas time for some extra Christmas money. Float seat assemblies (seat and needle) are really good these days. Gaskets are almost identical to the original but paper is higher quality on aftermarket. Jet needles are OK... match the taper of the originals fairly well as I have made extensive measurements. Mixture screws are faithful to the original; all this stuff is manufactured in Japan by the company that originally made these parts for Keihin and Mikuni and were sold as OEM. Not sure about Hitachi or Teikei carbs nor where the original jets were sourced.

Please tell me about your experiences as I am interested in why you are making claims that the aftermarket parts sold today are inferior. Not trying to start a flame war or argue, just not my experience and am interested in your experience. The KZ400 this fella has has several different carb assemblies and some are kind of complicated and individual replacement parts are not readily available for some of these parts. I have rebuilt over 50 sets of KZ400 carbs in various itterations over the years.

Well George, for one thing the float needles for the BS Mikuni's that K&L sells have a crap weak spring which will not hold up the weight of the float. The real deal Mikuni parts aren't like that. For another thing the OEM's often changed the jet sizes year over year within the same model, the GS650 for example, and most if not all aftermarket carb kits I've seen are not specific to the year so it's a crap shoot as to whether the jets are correct for your particular bike.

I'll take a real deal Mikuni and/or Keihin jet that's been cleaned in carb dip over any Kester/K&L/etc carb kit jet, new or otherwise. Cleaning them is easy and I've never heard of anyone having issues with changing the flow pattern by simple cleaning a jet, and that includes using a small piece of wire, such as from a stiff wire brush, to clean out any grunge left behind from the carb dip.

The other MAJOR problem with "carb kits" is it makes people LAZY. Guys think they can take off their carb rack, open the float bowl, remove the kit parts, shoot some carb spray down the passages, install their "new" parts and then go off riding into the sunset. Try hanging out here or at GS Resources and be prepared to read countless threads from guys that "rebuilt" their carbs when in truth, all they did was change a few parts. The pilot circuits are not clean and the fuel interconnect tube O-rings are not replaced, and as you know, those are the ones that turn rock hard and brittle. I put the over and under at THREE: the number of times people have to pull their carbs to properly clean them

As for my experiences, I wrote this tutorial... zeus.mtsac.edu/~cliff/storage/gs/Mikuni_...Rebuild_Tutorial.pdf
It's been copied and linked on all kinds of different motorcycle websites. I've rebuilt scads of BS & VM Mikuni's and CV34's such as KZ's used.

The only way I'd use aftermarket carb kit parts is if the original parts are damaged and I couldn't source replacements otherwise.

Nessism wrote: Well George, for one thing the float needles for the BS Mikuni's that K&L sells have a crap weak spring which will not hold up the weight of the float. The real deal Mikuni parts aren't like that. For another thing the OEM's often changed the jet sizes year over year within the same model, the GS650 for example, and most if not all aftermarket carb kits I've seen are not specific to the year so it's a crap shoot as to whether the jets are correct for your particular bike.

I'll take a real deal Mikuni and/or Keihin jet that's been cleaned in carb dip over any Kester/K&L/etc carb kit jet, new or otherwise. Cleaning them is easy and I've never heard of anyone having issues with changing the flow pattern by simple cleaning a jet, and that includes using a small piece of wire, such as from a stiff wire brush, to clean out any grunge left behind from the carb dip.

The other MAJOR problem with "carb kits" is it makes people LAZY. Guys think they can take off their carb rack, open the float bowl, remove the kit parts, shoot some carb spray down the passages, install their "new" parts and then go off riding into the sunset. Try hanging out here or at GS Resources and be prepared to read countless threads from guys that "rebuilt" their carbs when in truth, all they did was change a few parts. The pilot circuits are not clean and the fuel interconnect tube O-rings are not replaced, and as you know, those are the ones that turn rock hard and brittle. I put the over and under at THREE: the number of times people have to pull their carbs to properly clean them

As for my experiences, I wrote this tutorial... zeus.mtsac.edu/~cliff/storage/gs/Mikuni_...Rebuild_Tutorial.pdf
It's been copied and linked on all kinds of different motorcycle websites. I've rebuilt scads of BS & VM Mikuni's and CV34's such as KZ's used.

The only way I'd use aftermarket carb kit parts is if the original parts are damaged and I couldn't source replacements otherwise.

I have to agree here with Nessism, I recently purchased two 98' CBR600F3 that had been sitting for ~9 years. Just to test, I put fuel in one, hot wired the fuel pump and everything leaked in one form or another from the petcock to the intake. Fuel everywhere. I wound up replacing every piece of rubber in the fuel system on both. Also every orifice and circuit was gummed or clogged up. Not until I soaked it in carb dip did they finally get cleaned ( I had to do it three times). Point is, for me at least, I learned (again..I'm thick sculled )there are no short cuts when it comes to "rebuilding" carbs that have sat for a while. Just do the whole thing front to back and save yourself a lot of grief.

I buy float seat assemblies in bulk from an aftermarket source as I do most all parts for BS or VM carburetors and have no problems with any of the parts. As for kits making a person lazy, I am paid to rebuild carburetors and I totally disassemble every part and replace all orings in every rebuild. I don't "soak" carburetors which I did when I first started as the carb dip is nasty stuff and probably not good for your health if you rebuild for a number of years. I don't like carb dip in my shop. I do recall Berrymans was much stronger a number of years ago and they had those gallon cans blow up in transit when they got hot. I was told this by Berrymans folks who I believe were up in the DFW area. Anyway, they changed their formula so it didn't blow up in transit and this made it weaker.... used to dip in a parts washer tank. Today, I use a multi-frequency ultrasonic to clean internal passages and then flow test to ensure all are clean. I media blast to close the pores and provide a lasting clean finish. It generally takes me about 1 1/2 to 2 days to do a set of carb so fully agree there are no short cuts. I you do one set of carbs, perhaps the dip will work for you but in production, I just am not comfortable with the stuff for health reasons. I have limited brain cells.

Sorry to bring this back up but found an interesting quote on a website from a Honda specialist regarding carb rebuild kits....

www.motorcycleproject.com/index.html