Cold blooded 83 KZ 750 LTD

I have an 83 KZ 750 LTD F1 shaft drive bike that has a cold blooded issue and would like feedback as to whether this is normal. The bike has 19,000 miles. It starts right up with the choke, but takes about 5 minutes of warm up before I can take off without the bike bogging down to the point that I have to pull over to the side of the road. In other words, not very safe riding conditions. It will reach this condition again after cooling off after about an hour. When warmed up, the bike also runs perfect. I am hesitant t tamper with anything because it does start easily and also since it runs perfect once warmed up. I lived in toasty Texas and can even tell that more warm up is needed when ambient air conditions cool down from summertime 90's down to about the upper 70's. Is this all due to the ethanol in the gasoline? I use premium grade Shell gasoline. I hear that fuel injected bikes do not have this problem, and have seen on other message boards that riders are claiming that Iridium spark plugs remedy the cold blooded condition. Any feedback would be appreciated.

How long have you had the bike & did it sit for a while? It could be that the pilot circuits are clogged. The choke is actually an enrichening circuit, so using the choke will compensate for clogged pilots.

I have owned it for about 15 months and it has been the same during my ownership. I have run Seafoam through a few tanks of gas and have put 800 miles on the bike and there has been no change.

The owner I bought it from only owned it about a month and he reported it was cold blooded.

It sounds like you are saying even with ethanol in the fuel this is not a normal routine.

I appreciate your feedback.

Ethanol shouldn't cause running issues --- the primary complaint about the stuff is that it attacks rubber.
The starting the engine section of the owner's manual is a good guide for how to start & warm up the bike.

If it doesn't perform at least close to those guidelines, then something is preventing the engine from running properly.
Clogged pilot circuits would be at the top of the list. Your carburetors have polyester caps over the pilot jets & those caps may trap fuel in the passages, which then "varnishes" when left sitting too long. Maybe the idle is set too low or the carbs are out of synch. ???

Try using mid-grade instead of premium. The higher the octane the slower the burn. I tried a tank of premium in my GPz and it ran great once warm but it didn't want to start up. I went back to mid and it starts right up it's a bit cold blooded still but it's running well. I'm pretty sure it needs some carb tweaking but it will have to wait.

I think you are right that clogged pilot circuits are probably the culprit. If you do a general search for "cold blooded" and "motorcycle" you will find beaucoup search results reporting the same problem regardless of brand. That is why I suspected the ethanol.

I started out using the 89 octane plus grade and had the same problem,

It sounds like the carbs and jets all need cleaning. Once they get gummed over a period of time, Sea Foam and such additives will never clean them properly, even spraying carb cleaner through jets and passageways will rarely fully clean them out completely. If you draw a copper wire through a jet a few times you'll often find there is a surface layer of some sort of varnish, gum or corrosion that will not be removed by solvents alone, but will come free with the wire.Use a strand of copper wire as this is soft enough not to damage the jet or enlarge the orifice. I've had jets I've even soaked in carb cleaner for some time and thought they were clean, I've struggled to get the copper wire through the opening, but then as it removes the build up it can be quite a loose fit in the opening. The jet orifices are fairly small, a thin coating of whatever on all the surfaces will make the jet effectively quite a bit smaller and you will have issues as a result. The difference between jet sizes is very small in terms of dimensions, so a relatively thin layer can be like being 2 sizes down in jet size in terms of the remaining opening The openings into the enrichment tubes are usually very small and clog easily too, so often you are not getting full enrichment, or only on some of the carbs in the set, all will lead to it being very cold bloodied, as you describe.

Once you know they are all clean for certain, and know how it's running, you can then turn your attention to jet sizes, it's likely on an 83, if they are the stock jets, that it will be set to run pretty lean from the factory as this is the time they were battling emission criteria, so often a step up in jet sizes is beneficial to overall running. Take a note of the jet sizes while cleaning them, so you know what you currently have and then if it still seems to be running a little weak (check the plug color) you can try a size bigger.

I believe that model bike has Keihin carbs, so the choke is a real choke. When the carbs get dirty the choke plates tend to hang open too. The spring used to close the butterflies is really weak. This is one of the weaknesses of that particular carb design. So basically, the choke doesn't work when this happens. I'm not sure this is what's going on but it's a very real possibility. You might want to try removing the air filter and looking down into the back side of the carbs while moving the choke lever to see if the butterflys close down. Simple experiment anyway.

Of course the pilot circuit could be clogged up as well. How may turns open are the pilot screws? Basic starting point is 2.5 turns open but you can go more if the bike is too cold blooded.

A guitar string is good for cleaning jets. If the needles are adjustable you can set the clip one notch down to get the mixture richer through out the RPM range. If that doesn't work, one size larger pilot is called for.
Steve

Here is a photo showing the carbs with the choke butterflies closed. Again, remove the air filter and look down through the airbox to the back side of the carbs and make sure the butterflies close down when you activate the choke lever. If the butterflies don't close, you found the reason for the cold blooded driveability.