kz550 carb issues

I'm having a bit of trouble with my carb settings for my 81 kz550-A2. Bike has a mac 4-1 exhaust and emgo pod filters. I know this subject has been beaten to death on here and I'm still reading other threads, but I was hoping someone could point me in a more specific direction. I'm just having a hard time understanding what my actual problem is and therefore I don't know how to begin crafting a solution.

I've got the dynojet kit for my carbs (manual slide type carbs) and I've installed the recommended #98 main jets and the dynojet needles with the clip at the 3rd position down from top, no washer shim. The bike will idle properly for the most part. The bike accelerates OK from 0 to 3k rpm with light throttle. around 1/2 throttle the bike seems to stumble a bit as if it's not getting proper fuel. To me that would suggest it's lean and that the needles need raised to richen the mixture. What confuses me now is that at WOT it will bog down heavily as if it is way to rich. Sometimes I get random spurts of power in the middle of that heavy bog down.

I did try increasing to 102 main jets and raising the needle one clip, but the bogging pretty much got worse and I noticed my plugs getting a little more black, so that was too rich. I also tried the #98 jet with the needle at the 2nd clip from top with shim under it (.5mm leaner than recommended). The response was slightly better but still not good, and I had a lot of exhaust popping, so that was too lean.

So all in all I'm experiencing poor acceleration at almost all of the powerband. I have been playing with the jet sizes and needle height for a few weeks and I am finally stumped enough to ask you all for guidance, even though the general consensus seems to be against pods.


one last thing, I went to get some new fuel line from the autoparts store and all they had was 1/4" (ill go to napa next time) It seems like the diameter is too small for the petcock and carb fuel inlet, but after warming up the hose end I was able to squeeze it on. Could the fuel hose be too small and be restricting fuel? The other thing I haven't looked into is float height. I kind of eliminated that as an issue though because before I changed exhaust and air filters the bike ran without any issues. Thanks in advance guys

here's some quick pictures of my project btw

jwe2 wrote:

...81 kz550-A2...went to get some new fuel line...all they had was 1/4"...diameter is too small for the petcock and carb fuel inlet, but after warming up the hose end I was able to squeeze it on. Could the fuel hose be too small and be restricting fuel?...haven't looked into is float height....

Helps to dip end of tube in near-boiling water immediately before attaching to nipple.

1/4" size is NOT restricting fuel, as fuel will flow through plenty fast to maintain levels inside the float bowls.

Measured float height is not the critical factor

Fuel level inside the float bowls is the critical factor. Use the clear tube method to determine fuel level.

Good Fortune!

I have not worked on a 550, I have a 650, but when I did my mods way back in 77, I purchased several different jet sizes (both pilot, main and needles) but found the stock needle worked best for me. If dynajet kits were available then I did not know it. I am not sure what all they provide it the kit. But from what I can find on line it looks like the kit does not come with a pilot, is that the case. When I added the pods and 4 to 1 I had to up the pilot 1 size and the main 4 sizes. But I tried several different ones to get there.

The bog you have at 1/2 throttle is most likely related to a needle issue either the clip setting or the taper of the needle itself. What is the difference between the needle in the kit and the stock needle. Have you tried the stock needle with the jets from the kit.

I have found the attached doc to be of great use when tuning. It did take lots of trial and error to get it right.

Did it run properly before all of the changes?

That Dynojet kit should cover most issues except one. I find with the Dynojet kits, you have to also use larger pilot jets to get the part throttle action to work properly. Raising the needle won't change the idle-to-1/8th throttle very much.

If you stick with the Dynojet needles, you will probably want #37 pilots (stock is 32), but you can't get them. You have to drill them.

Another option is to get rebuild kits which come with adjustable versions of the stock needles, and set them at the 3rd notch from the top. They have two tapers. The first one starts earlier, but is more gradual. This makes the mixture richer just off idle than the Dynojet kit. This will reduce the need for new pilots. The problem is, there will be a slight lean spot at about 1/4 throttle, but it may not even be noticable.

Here is the profile difference in the needles:

Here is the relative layout of the needle position in the carb:

By the way, the Emgo pods and the Mac, each separately required quite a bit of small throttle enrichening on my GPZ 550. Together, I would imagine they would require quite bit.

If you only have the dynojet or stock needles, you may want to try raising the needle, but going back to the stock main jet.

There is one other major issue in regards to the WOT (wide open throttle) position. The TK-22 carbs allow you to set the WOT position. Sometimes they are set where the throttle will actually go beyond fully open. This means, as you go past the 100% open slide, you will add more fule, but no more air. This makes the mixture get much richer at WOT.

If, as you roll off the throttle, the bike seems to go faster, then you should check the WOT stop. The drawing above shows how to measure the slide position for WOT by taking off the carb tops. But since you have pods, you can pull off the carbs and look into the engine side of the carbs. That is the side you need to see in order to set the slide flush at WOT.

If you look in from the air horn side, you should see the edge of the slide on the engine side flush with the roof of the bore.

Also, make sure to sync the carbs and set the air screws for best idle.

Nice write up loudhvx -

I did have the bike running fine before I changed the exhaust and airbox. I've been curious about the effectiveness of the dynojet needle because changing it didn't seem to help me. Yesterday I tried raising the needle one clip while staying with the smallest jets from the kit (98) and it didn't help at all. I do have those adjustable stock taper needles from a rebuild kit so I'm going to try using those. If that doesn't work I'll go back to the stock main jets, and then back to dynojet needles and stock jets if all else fails. I know all machines are different, but I'm surprised I'm getting such different results than others who've said they used the same settings as me with the same modifications.

one other note. the first day that I installed the kit with 98 mains and 3rd clip needles, air screws at 3/4 turn, I ran the bike around town most of the day and it ran nice. screamed up and down the block and i was very happy with it. that night riding it home it had problems, but I kind of chalked it up to the drop in temp and the bike not being warmed up. but the next day was normal temp and I had these issues again, thus I started playing with the settings. my carbs have been cleaned very well and I have an inline fuel filter so I have a hard time thinking I fouled up the fuel circuits already. Just thought that was worth noting. Thanks

Yes, that is interesting. If it ran fine the first day, I wonder if something happened that night. Have you checked all four plugs to see if any one or two are different from the others?

Usually, installing the Dynojet kit gives decent ridable results at first installation. As I said, the pods and Mac combo do need more fuel at low throttle than most airbox/4-into-1 combos. It is troublesome that it seemed ok the first day. That would indicate something changed/broke etc.

Have you read the instructions with the Dynojet kit, if you have them? It is pretty lengthy, and the testing takes a long time, but it works well and is a good alternative if you don't have an O2 sensor handy.

Here's a copy of it: home.comcast.net/~loudgpz/DynojetKitInstructions.pdf