1976 KZ400 questions

As most of you know, i just bought a 1976 KZ400S2. i got it running today after cleaning the carburetors last night. It runs but it idles high and the idle screw on the side of the carb isn't even touching the throttle assy. anymore so according to it, its closed. i know i have a vacuum leak somewhere. I need new manifold boots for it because these ones are cracked up bad. i patched them with some silicon and electrical tape but they still aren't sealing. i was wondering if maybe somebody on here might have some boots that they might sell me? the bike revs but the diaphrams don't seem to move up and down... i know they aren't stuck. Is it even possible for the bike to rev if the diaphrams don't open? Also, will the bike run like crap, or not at all with a dead battery in it? mine had a battery in it, but after i while i had to jump it off the car to start it because it went dead after it dying and me restarting it all the time because i couldn't get the carbs right. I would start it with it hooked up to the car battery and as soon as i removed one of the clamps on the jumper cables, the bike would idle way down and die... do you guys know if maybe the bike has a bad charging system? I'll start downloading the manual tonight on that one website but i was wondering if maybe you guys knew what the spark plug gap was for this? I'll post a video of it running:)

Thanks guys,
KT

Kitten Tooth wrote:

As most of you know, i just bought a 1976 KZ400S2. i got it running today after cleaning the carburetors last night. It runs but it idles high and the idle screw on the side of the carb isn't even touching the throttle assy. anymore so according to it, its closed. i know i have a vacuum leak somewhere. I need new manifold boots for it because these ones are cracked up bad. i patched them with some silicon and electrical tape but they still aren't sealing. i was wondering if maybe somebody on here might have some boots that they might sell me? the bike revs but the diaphrams don't seem to move up and down... i know they aren't stuck. Is it even possible for the bike to rev if the diaphrams don't open? Also, will the bike run like crap, or not at all with a dead battery in it? mine had a battery in it, but after i while i had to jump it off the car to start it because it went dead after it dying and me restarting it all the time because i couldn't get the carbs right. I would start it with it hooked up to the car battery and as soon as i removed one of the clamps on the jumper cables, the bike would idle way down and die... do you guys know if maybe the bike has a bad charging system? I'll start downloading the manual tonight on that one website but i was wondering if maybe you guys knew what the spark plug gap was for this? I'll post a video of it running:)

Thanks guys,
KT

Whoa, that's alot.
High idle like that is due to air leaks or lean condition. Could be incorrect float level, choke problems, or air leaks like you suspect. Stock manifolds for the '74 - '76 KZ400's are rare (though you can stumble upon a set once in awhile), so many people are forced to try and find ways to seal old ones. You might also want to make sure the manifolds you have are seated well against the cylinder head. Warning though; if they are stock, and you try to remove them, you will likely break the two screws holding them and you will have to drill them out...

I recommend you continue your plan to get the manual, then sit down and read the whole "Theory of Operation" carb section. So much more will make sense to you. Like for instance, these early models don't have diaphragms, they have an all-metal piston that lifts the main jet needle. The butterflies are opened with the throttle, and that is the revving you noted. The piston will rise as needed if it is able to...

The battery symptoms you describe sound about normal for a dead battery. Honestly though, I've been running my 400 for years on an almost-dead battery. Have you ensured that your possibly-dead battery is topped off with distilled water? and there are ways to test the charging system... I believe that's outlined in the manual too...

And wouldn't you know it, I don't remember the plug gap off the top of my head, but I know it's in the manual...

I'm checking this on my dad's computer because mine is shut off at the moment. I have already removed the maniflod boots and the screws came out easy, thankfully. I found that there are two nossels on the side of each carb that are for a sync tool and they need to be capped off. Of course, there are no rubber caps on those so there was one horrible vacuum leak there. I believe my dad has alreadsy ordered some manifold boots off of a website that we found. The ones taht i have right now are pretty jacked. I have some clear fuel line now so i'm going to check the float levels. I'll seal the vacuum leaks and install the battery that i have been charging all night so far on a trickle charger. The battery is good, juist dead. I found the diaphragm thing when i pulled them apart, thought it was odd. Thats because they are mechanicle right? I'm sure the job i did was good, i just have to seal the vacuums and it should run great.

Thanks for the reply:)
KT

If the alternator is in working order, the battery can be almost totally dead and it will run fine. As long as the battery isn't shorted out, and has enough juice to energize the alternator it will run fine. My buddy used a dead battery for three years and never had any problems (his was a kickstart-only model). The battery couldn't even power the tail light (or maybe brake light) by itself. I it did show 11v or so when not connected, but had almost no power when the bike wasn't running. After starting, the bike had full electrical power even at idle.

EDIT: I should add, with a totally dead battery, you should have the headlight turned off to start. A headlight acts like a short until the filament heats up. A dead battery may not have enough energy to heat the element so the voltage will stay too low to start. (On my firends bike we wired the ignition switch to have a position with just ignition and no headlight.)