'78 kz1000 -- What carb main jets/pilots are good?

1978 kz1000 A2 standard model, with original carbs but jet changes -- as described below.

I think my jetting choice may not be correct -- this motor has an 1137cc kit in it with custom cams and electronic ignition -- shouldn't this bike be lifting the front end?

It has a 'Kawasaki by Kerker' 4-into-1 pipe but it is restrictive, it *must* be as it is a VERY QUIET 4-into-1, I mean close-to-stock quiet. Maybe a different 4-into-1 is needed that's louder and less restrictive.

The bike has lots of torque off the bottom but I can't say that it has 'explosive' power much above, say, 3000rpm.


My jets are:
* main jets: #120 (stock mains were #105)
* pilot jets: #20 (stock pilots were #15)
* needle clip: moved down one notch, to position #4,
thus raising the needle one notch

I went from stock #105 mains and #15 pilots and changed the needle because -- the prior owner did NOT change the carbs jetting, despite the fact that he made the following changes:

- 1137cc kit

- 4-into-1 Kerker (restrictive, quite 'street' baffle)

- hotter custom cams

- Gerex electronic ignition

- removed the black plastic triangle-shaped rearmost airbox piece that connects with a tube to the air filter container. All that's left is the stock air filter box with a big opening where that triangle+tube box used to be.



With all those changes but stock carb jetting -- I figured he must have been running lean!!

So I have already changed from #105 mains to #120 mains and pilots from #115 to #120, and dropped the needle clip one notch.

DO I NEED BIGGER MAINS HERE? Shouldn't this bike, with nearly 1200cc, cams etc. be pulling my arms out of the socket?

If not already done, would start cold engine and allow to run about 15 seconds, then spray water mist on header pipes to assure combustion in all four cylinders.

Spray should sizzle and instantly vaporize. If water runs down pipe, the cylinder isn't combusting.

Would assure good quality properly timed spark on all plugs and acceptable compression in all cylinders before further addressing carbs.

Just the way I would approach it.

Good Luck!

I run 120 mains on a stock engine with pods and open pipe.

There are diffrent baffles for the Kerker. Sounds like you might want a compention baffle.

I installed 122.5 jets in a Shaftie Saturday. It had pods and open pipe and the bike came alive. I have a set of 120's that will be installed this week. I think that will be closer. Roy


I have learned,before you do any carb work to follow the suggestions that patton mentioned and check your valve clearance. Learned that the hard way. Roy

Hello everyone. Being new to the site, I hope you will bear with me until comfortable with responding to or asking questions. I recently went over carb issues with a much milder setup but in the process found to my surprise that 120 pilots were actually smaller in I.D. than the 115 size. I was using a very small drill index to try to determine the internal size of the jet when making changes to put a decimal size to it. It would seem as though it relates to wire size which means the smaller the number, the larger the wire. You may want to go back a size with the pilots to see if you get better results.
Good luck!

Kawboy74 wrote:

Hello everyone. Being new to the site, I hope you will bear with me until comfortable with responding to or asking questions. I recently went over carb issues with a much milder setup but in the process found to my surprise that 120 pilots were actually smaller in I.D. than the 115 size. I was using a very small drill index to try to determine the internal size of the jet when making changes to put a decimal size to it. It would seem as though it relates to wire size which means the smaller the number, the larger the wire. You may want to go back a size with the pilots to see if you get better results.
Good luck!

I get what you're saying about the 'irony of wire size' -- an 18-gauge wire is thinner, MUCH thinner, than, say -- 12 guage wire. 12 guage wire is fine for 15amp service in a home wiring situation -- 18 gauge might well get so hot it starts a fire (though there's not too much wire to burn at 18 gauge size).

However, jet sizes (I'm pretty sure) are logical -- a 120 main jet flows more gas than a 105 main jet.

I have proven this to myself in practice, here's an example. A while back when a Kaw triple I worked on was running so lean it was lurching (they call it the 'lean lurch') at all parts of the throttle position: 0-1/8 throttle (pilot), 1/4-3/4 throttle (needle jet + main) and 3/4 to WFO (main jet).

I went up 2 sizes on the mains, 2 sizes on the pilots, and moved the needle clip down 1 notch to raise the needle in the carb body. PRESTO no more lean lurch and the bike ran so hard I had to install heavy duty clutch springs and all new clutch plates to stop it from slipping as it came on the power. The bike went from a 'lean lurch' condition to popping wheelies just by going up 2 jet sizes.

As to the pilots' i.d., perhaps there's more to it than that. Here's a photo of my pilot jet being removed -- look at the holes in the lower shaft of the pilot jet, they play a role in fuel delivery too:



I consider myself a 'raw beginner' too, however with a factory shop manual, some metric tools, and a can of diet Pepsi I quickly come to believe I'm 'channeling' Irv Kanemoto.