Idle issues

I finally got the bike out today, and she runs good, for the most part.

When the engine is cold, it idles good, about 1000-1500 RPMs. Once it gets hot, it idles between four and five grand. While driving, everything seems fine, unless I make a real slow shift, like hold in the clutch for a second or more, then it idles up. I don't know much, but I'm a little puzzled why it runs better cold than hot. My first guess is that the throttle is sticking, but I don't really understand why it would only stick when it's hot. While driving, releasing the throttle causes it to coast slowing down, which seems to shoot a fairly large hole in my theory. Any insight would be much appreciated.

By the way, it's an 80 kz750h (LTD-4).

Could be a few things. Could have a vacuum leak that gets bad when it warms up as things expand. Or the slides inside could be sticking. Could even be inside the engine. When you rev it up does it come down to an idle quickly or does it float for a while? The throttle cable doesn't need to stick for the idle to stay up. My carb slides were sticking so they had to be lubed up really good. Not enough info to really say just exactly what it could be.

Have you changed anything since the last time it ran well? It could be something as simple as your idle adjustment screw. Also the cable has a few points where it can be adjusted. I would suggest starting with these simple fixes.

I just bought the bike, so I have nothing to look back on. I did speak to the PO, and he said he never had that issue, but it did sit for about a year in his garage. The tank was drained though. It came with no air filters, but had pods, and I put pods back on, so I don't really think that changed anything, and I don't know if the PO before the guy I bought it from adjusted the carbs or not, but it runs well accept at hot idle.

I also like the idea of starting simple.

When I rev it up cold, it drops back down just like I think it should. I've never really revved it hot as it is already at five grand or so. This morning when I pulled into the parking lot at work, it was up around five grand while clutched, but when I put it in first gear, the RPMs dropped to around 2000-2500 while I was putting along to park. I'm not sure if that gives any clues or not.

I hope it's not a vacuum leak, as those can be a real PIA to track down.

Air leak on carb boots/holders (those rubber "hoses" connecting carbs to engine intake). Those are not too expensive just first change them. www.z1enterprises.com/catalog.aspx?pid=KPCF0

Z1109R Fin wrote:

Air leak on carb boots/holders (those rubber "hoses" connecting carbs to engine intake). Those are not too expensive just first change them. www.z1enterprises.com/catalog.aspx?pid=KPCF0

I've visually inspected them (while on the engine) and they looked ok. But that doesn't mean that they don't leak and I can't see it.

I've put about 240 miles on the bike since Saturday, and the problem seems to slowly be getting better. I guess it could just be from sitting for a year or so, and might just correct itself. I think right now, I might just put some more miles on, and see if it changes at all.

You can check for leaks on the carb holders really easily. Just spray some WD40 or carb cleaner all over them while the bike is running (hot because that's when you have problems). If it changes your idle at all then you have a leak there. Easy enough.

Check leak like anarki650 said. Then check throttle cable and slides. Slides must come down all the way leaving only a minimal opening for air. Just 1 mm = .004" too much can keep the engine revving like h@ll. Also check the manual idle screw, make shure it´s all the way down. Even the slightest opening of slides will keep the engine revving.

I checked for leaks with WD40, and all is well. I can check the carbs as best I can. I realize I know next to nothing, I just don't understand why the problem would only be when it's hot if it's the carbs.

Go to the local auto parts store or wally world and buy a can of "seafoam", its a gasoline additive(some call snake oil) but will really work in cleaning out the fuel system in your bike. The forum at www.kawasaki.org/forum touts it's ability a lot.

I'm just running around resurrecting dead threads today.

MFolks wrote:

Go to the local auto parts store or wally world and buy a can of "seafoam"

I poured some seafoam into the last two tanks of gas, and it has made no difference, other than maybe the engine needing to be a little hotter to rev high than before, and that's a stretch.

I gave the fuel lines a quick inspection on Sunday, and everything appeared to be in order, but I really need to get a manual so I can be more sure about things.

The only guess I can come up with right now for the culprit is something sticking when it gets hot. I just would've thought that would be a little less regular, and that it would've gotten better or worse in this amount of time.

I have no idea what I am doing as far as checking the carbs, so I think I'm going to have to wait until I get a manual to do that. If anyone can offer any other theories to check, I would appreciate it. The easier the test, the better, cause I'm a real noob.