81 kz550 weird running issues

Ok guys my 81 kz550 is very temperamental. From a cold start it takes about 10 solid minutes to warm up before it will idle on its own without choke. The idle will also be to low still and won't idle roght until you ride it a solid mile or 2. Once it's warm it runs awesome and idles nice.

Also say I already had it running today and rode it etc. if I turn it off and park it for 30 min or so and it cools down it won't start nice again. You gotta give it a little choke and let it warm back up again.

I have synched the carbs and if anything it has made it worse then it was. When cold starting with the choke on it kinda starts hard and will want to immediately rev up to like 6k rpm. Not sure what's going on with it since once the engine is warmed up hot it runs amazing.

Have you ever torn down the carbs and cleaned them thoroughly? Replaced all the O-rings? Played with the air screw setting?

Also, if there have been any mods to the bike, including using a non stock exhaust or air filter(s), you have to rejet the carbs.

Lastly, if you haven't adjusted your valves lately, do so.

Sounds like you have a vacuum leak at the intake boots. Spray some carb cleaner at them and listen for a change in idle

Good suggestions in this thread, however this

From a cold start it takes about 10 solid minutes to warm up before it will idle on its own without choke. The idle will also be to low still and won't idle roght until you ride it a solid mile or 2. Once it's warm it runs awesome and idles nice.

are characteristics of the 550.

The KZ550 needs the choke when cold, and it has to warm up somewhat to run properly.

What are your air screws set at? Setting these richer (screw in) will allow easier starting and allow you to come off choke sooner.

What is your fast idle set at? Turn this screw in to increase idle speed with the choke on. In my experience this needs to be adjusted with seasonal changes. Yours may be set too high if you rev up that high with the choke on.

Do you have all the choke flaps? May be missing a couple. If you have glued them shut it takes more care to start the engine.

Nessism wrote: Have you ever torn down the carbs and cleaned them thoroughly? Replaced all the O-rings? Played with the air screw setting?

Also, if there have been any mods to the bike, including using a non stock exhaust or air filter(s), you have to rejet the carbs.

Lastly, if you haven't adjusted your valves lately, do so.

I only just bought the bike recently. I have not gone threw the carbs. Only synched them. The only mod on the bike is a Vance and Hines 4 into 1 exhaust. Not sure of the jetting as of yet.

The_Proletariat wrote: Good suggestions in this thread, however this

From a cold start it takes about 10 solid minutes to warm up before it will idle on its own without choke. The idle will also be to low still and won't idle roght until you ride it a solid mile or 2. Once it's warm it runs awesome and idles nice.

are characteristics of the 550.

The KZ550 needs the choke when cold, and it has to warm up somewhat to run properly.

What are your air screws set at? Setting these richer (screw in) will allow easier starting and allow you to come off choke sooner.

What is your fast idle set at? Turn this screw in to increase idle speed with the choke on. In my experience this needs to be adjusted with seasonal changes. Yours may be set too high if you rev up that high with the choke on.

Do you have all the choke flaps? May be missing a couple. If you have glued them shut it takes more care to start the engine.

Where is this fast idle screw you speak of? I do have all the choke flaps etc.

your idle screw is to set the idle setting it's on the left side ,i agree your jets are probally very dirty,go to a pro paint shop and get air nozzle cleaning needles ,these are the only needls that will run through the passages freely to dis lodge crap ,carb cleaner is ok but you still have cleasnup ,or soak them in varsol or disel fuel , your air jet is set to 3 turns backed off from closed ,it's your starting point ,make sure your not overheating on idle ,remember this is a free air ,over 4:00 mininutes could cause damage,but definitly your carbs ,you can also soda blast before starting your final cleaning to remove varnish in bowls and dirt on exterior..

Wildman1024 wrote:

The_Proletariat wrote: Good suggestions in this thread, however this

From a cold start it takes about 10 solid minutes to warm up before it will idle on its own without choke. The idle will also be to low still and won't idle roght until you ride it a solid mile or 2. Once it's warm it runs awesome and idles nice.

are characteristics of the 550.

The KZ550 needs the choke when cold, and it has to warm up somewhat to run properly.

What are your air screws set at? Setting these richer (screw in) will allow easier starting and allow you to come off choke sooner.

What is your fast idle set at? Turn this screw in to increase idle speed with the choke on. In my experience this needs to be adjusted with seasonal changes. Yours may be set too high if you rev up that high with the choke on.

Do you have all the choke flaps? May be missing a couple. If you have glued them shut it takes more care to start the engine.

Where is this fast idle screw you speak of? I do have all the choke flaps etc.

Between carb 1 and 2 on the linkage.

The only mod on the bike is a Vance and Hines 4 into 1 exhaust. Not sure of the jetting as of yet.

May or may not need to do some jetting work,

your air jet is set to 3 turns backed off from closed ,it's your starting point

This is incorrect. 1 1/8 is factory setting. You should be pretty close to this. Each carb may need to be slightly different.

Wildman1024 wrote: Ok guys my 81 kz550 is very temperamental. From a cold start it takes about 10 solid minutes to warm up before it will idle on its own without choke. The idle will also be to low still and won't idle roght until you ride it a solid mile or 2. Once it's warm it runs awesome and idles nice.

This sound normal to me. I've only owned my 550a (looks like a twinkie of yours but in black) since Feb. I've ridden it ... I've filled up the tank 4 times now. It gets about 38mpg if I ride it sanely. I have to use full choke - all up and then beyond to the "click" to start a cold engine (cold being relative here, I mean not run recently).
Point is, this starting ritual seems fine. I think it was on this forum that I heard the 550 described as "cold natured"?

Wildman1024 wrote: Also say I already had it running today and rode it etc. if I turn it off and park it for 30 min or so and it cools down it won't start nice again. You gotta give it a little choke and let it warm back up again.

I am not phased by this. Same same. Cold natured bike. Makes us appreciate fuel injection a little more huh? :laugh:

Wildman1024 wrote: I have synched the carbs and if anything it has made it worse then it was. When cold starting with the choke on it kinda starts hard and will want to immediately rev up to like 6k rpm. Not sure what's going on with it since once the engine is warmed up hot it runs amazing.

I attempted synch on my carbs multiple times too and I still think I could do better. It's definitely a finicky task. As to the fast idle adjustment... I don't think my adjustment screw is typical because it has a larger (like 13mm) nut threaded onto the top. It makes it really easy to adjust while running though... So I do. I've taken the 550 out for a whirl and (often at first, when it was new to me) pulled over to the side of the road and adjusted it. Maybe the PO knew about 550's finicky cold natured behavior? :huh: Something I do when I adjust it though is to pull the throttle just a wee bit to unload this screw and it makes adjusting it a breeze. With the nut it's even breezier

No amount of carb dismantling and cleaning I did (completely torn down to the bones, 3 times, replaced every part you can 2 times) ever changed this "cold natured" starting routine. Even when the day temps are in the 90's I'm still using choke to get'r started. I'm just used to it's behavior now and accept it. If it weren't for the fact that it goes like lightening and continues to pull like a runaway freight train to redline; I'd be worried and if I ride it "normally" I get great gas mileage so who am I to argue with a touchy need for choke? I need more coffee to get going when cold too now :laugh:

The throttle adjustment screw for the choke. Is that the Phillips screw in the bracket on the shaft that runs between the carbs? Anyone have a pic just so I'm sure?

I just took a pic of mine but can't seem to upload it from my phone. Ill upload it from pc here in a few minutes.
But yes, there is a screw between carb 1 & 2. Sticking straight up along front edge.

OK. Here's a pic of the screw in question. Mine has a 13mm nut on the top so it can be adjusted by hand while riding (well, pulled over but while out on the road). I don't think this nut is stock but was added by the PO.



Hope that helps!

Once the engine is properly tuned up, you should not have to touch the idle adjustment screw until the next tuneup.