1979 kz400 idle issues

So I picked up a 79 kz400 about a week ago to build a sweet little bobber with. Bike has pod filters, and no air box. The main issue right now is getting the bike to run smooth and consistently. When I got the bike, I was told it had been sitting for about a year. Got it home, put new plugs in it, cleaned out the carbs, etc. Tank wasnt on the bike, so I sprayed some starting fluid in it and she fired right up. Idled smooth around 1200 rpm. Got the tank on Sunday, put gas in, started the bike up. It ran really rough, then the rpms just ran away, cut the bike off at 7500. Started the bike back up a few minutes later, and it went straight to 7500 and I shut it off. The bike wont start at all withthe choke on, all of this happens with it off. Tried tp give it some more love today, completely recleaned the carbs, put them back on, and same thing. Bike went straight to 7500. Does anyone have any idea what could cause this?

It sounds like it could be a combination of vacuum leaks and the carbs not being jetted to run with pods. You need to increase the sizes of your jets from their stock settings for a bike to run smoothly with pods. It's usually best to get an air box to use until you get the bike running right and then decide to leave it stock or switch back to pods.

Would the pods make the rpms jump a ton like its doing though? This is my first bike, and I'm new to kawasakis. From what a friend told me the pods would just make it run lean, and bog down.

When I had pods on mine that weren't jetted correctly my bike bogged with any acceleration and died. The racing rpms are most likely a result of leaky carb intake boots. You should first check the jet sizes in your carbs and compare them with the stock sizes. If they are stock it will be difficult to diagnose a vacuum leak using the carb cleaner spray test as the bike may not be running correctly due to the jets. Once you check that and adjust it if necessary you should be able to get the idle to where it won't be out of control. You want to adjust the idle knob on your carbs to the lowest possible idle without stalling and spray carb cleaner at your intake boots. Any change in idle means you have a vacuum leak

well see, the thing i really dont understand is the fact that it will run perfectly fine if there is no fuel source (gas tank off) and i just spray starting fluid into the filters/some in the fuel line. it idles fine, it revs fine, the rpms drop, everything is good if the tank isnt hooked up.

Do you have any rust in your tank that could have clogged your carbs up?

No, tank was acid bathed before i got the bike, tank was spotless. found out last night that the tank has a serious leak all the way down the right seam. kind of pisses me off, but oh well.

A classic cause of racing idle is air leakage through the carb holders or at the carb holders.

The carb holders may be cracked (a crack is sometimes difficult to see), or the clamp holding the carb into the carb holder might be loose, or the carbs might not be inserted completely into the carb holders.

The carb holders aren't supposed to look like these:




If the spray test for leaks is done with WD40, exhaust smoke will appear, which shows that WD40 is being ingested at the carb holder area.

Carb cleaner or propane may also be used for test spraying at low rpm, which will cause a change in rpm due to ingestion; however, propane likely won't produce the tell-tale exhaust smoke. But I'm uncertain as to exhaust smoke from ingesting carb cleaner as compared to ingesting WD40.

Good Fortune!

Okay cool, thanks alot guys. Im going to get the tank down to bare metal tomorrow to figure out where its leaking, and check out the carb holders.

Patton wrote: A classic cause of racing idle is air leakage through the carb holders or at the carb holders.

The carb holders may be cracked (a crack is sometimes difficult to see), or the clamp holding the carb into the carb holder might be loose, or the carbs might not be inserted completely into the carb holders.

The carb holders aren't supposed to look like these:

If the spray test for leaks is done with WD40, exhaust smoke will appear, which shows that WD40 is being ingested at the carb holder area.

Carb cleaner or propane may also be used for test spraying at low rpm, which will cause a change in rpm due to ingestion; however, propane likely won't produce the tell-tale exhaust smoke. But I'm uncertain as to exhaust smoke from ingesting carb cleaner as compared to ingesting WD40.

Good Fortune!

Well, decided to mess with it a little when I got home from work. The current issue im having is getting the carb boots off. I sprayed the screws with wd40, let it sit for a while, tried to break them loose. All that happened was I started stripping the heads of the screws. Not completely sure how im going to get them, but me and a friend are going to try and figure out the idle issue tomorrow after work. The end of the holder where the carb mount looks almost brand new, but where it bolts to the head the rubber is breaking off and cracked apart.

You should use soak the screws in penetrating oil like Kroil or Liquid Wrench for a few days before you try to remove them. If you strip the screw heads they will be very hard to take out

Don't further damage the heads of the screws.

The screw threads are most likely corroded in position.

Would keep the screw heads wet with Kroil (or Liquid Wrench or PBBlaster or other penetrant) for a few days before attempting to remove (unscrew) them.

Without twisting, insert a driver tool and tap-tap-tap the end with a hammer to help jar the threads loose, which may allow better penetration.
Do this several times during the soaking process.

When soaking is complete, would also heat the engine area and top of the screw with a butane torch just before attempting to initially break the screw loose.
This is because the aluminum will expand more than the steel screw, and hopefully serve to loosen the aluminum female threads' grip on the male steel threads of the screw.

When replacing the carb holders, use new allen head screws.
And put a dab of anti-seize on the screw threads.

Good Fortune!