TOPIC:

Hey all, I just got a kz 400 thats been sitting for awhile and I got it to start, and it does fairly easily, but it kinda revs up and down between 1 and 4k (which could be cleaner etc. in the tank, lines and carb) and when I take the choke off it dies...any ideas???? its a 76, probably hasnt been run in at least 5 years

and why does the pilot jet have a cap on it???

It probably needs a good cleaning, running cleaner through it may or may not work. The idle jet is probably completely clogged because the engine dies when the starter jet is closed and it has no way to get fuel and air. I assume the cap you mean on the "pilot jet" is the pilot air screw. It's there to keep people from tampering with the mixture...you can drill it out relatively easily, you may have to to fully clean out the passages.

yes, if you were to look at the mainjet, there would be a plastic cap on one of the passages next to it, in that tube there would be a fairly normal looking jet..ie a small threaded cylinder with a hole in it, now in the same tube there would also be another which looked like a threaded tube with holes in the sides (like an air corrector), will it be easier to run if I take out that plastic cap, the first jet, or the tube? or do they have to be in there, they all came out very easily when I cleaned out the carbs the first time, could be theyre still clogged up, it was pretty messy in there, I was just wondering if anyone else had tried this so I dont have to keep pulling the carbs

also, when I say that taking the choke off makes it die, I mean its like hitting a kill switch, although I got it to fire when it was flooded out without the choke on, so I guess that would indicate a horribly lean carb..heh its my first bike I'm used to scooters and their simple engines! thanks for any help anyones got!

Good information so far, but here's the man you'd need to seek out.....

www.kz400.com/

Not sure if I'll have anything helpful to add, but here goes, cause I just went though this.

You're idle jets are clogged if its dying with like that with the choke off. Mine was just doing the same thing a month or so ago when I bought it. I tore it all apart and used some extremely fine wire to clean out the removeable parts, but didn't have anything for the internal passageways of the carb body, but it fired up and runs great, though the idle is still off a bit (extremely high), but it will run with the choke off now. I've been told that there is some heavy duty carb cleaner stuff you can soak just the metallic parts of the carb in to remove everything that might be gunking up the inside, but haven't had the chance to try it yet. I can vouch for a can of compressed air going a long way with this stuff though.

Bugg,
Regarding the plastic cap - if it's like the one at 3 o clock in the pic below then it has to be there. The feed for the idle jet which is under the cap is taken through a bleed pipe or connection with the main or primary jet

The variation in idle speed sounds like there may be an air leak in the pilot system. The slow jet is beneath the plastic plug and draws gas from the main jet tube next to it. If the plug is missing, the idle will be excessively rich and will bog. Choking will make it even richer and that doesn't match the symptoms you describe. The variations sound like air is being drawn in where it shouldn't. The normal source for this problem is worn and hardened orings that sit between the pilot mixture screw and the screw to provide a seal. You first need to drill a small hole (1/8" drill bit) through the plug over your mixture screw. Don't use much pressure as you will go all the way through and hit the screw head. Once you go through the cap, use a nail to pry it out. Once you have the cap out, then turn your pilot mixture screw IN until it lightly seats and COUNT the number of turns so you can replace it in the same position after you remove it. The pilot mixture screw is held in place by a spring which tensions the screw so it doesn't vibrate out... Once you remove the screw and spring, you will need a small tool to pull out the very small washer and below it an oring. I use a dental pick for this purpose. The o-ring should be replaced. The screw itself has a VERY sharp tip so take care not so seat it tightly as the tip will just snap right off. You can get replacment parts in a K&L Economy rebuild kit which will also give you a new float needle and a new bowl oring gasket along with the mixture screw parts. These can be purchased from www.z1enterprises.com.

Bugg, do NOT use a drill on those carbs. There are no caps covering the pilot screws.

The plug covering the pilot AND the slow jet are made out of RUBBER, not plastic. If it is hard as plastic, it will fail to seal properly.

The reason it will run when you apply the choke even if the pilot and slow jets are clogged is that the starter system is fed by a separate jet, and it gets air through a separate passage. This mixture is bypassing the carb throut and the outlet is located between the carbs and the mounting plate.