Author Topic: 1978 kz400 carb tuning, k&n pods and open pipes  (Read 372 times)

Offline AspireCycle

  • Posts: 2
1978 kz400 carb tuning, k&n pods and open pipes
« on: Apr 16, 2017, 23:47:50 »
Just finished getting my bike all tuned up. I call it the "Womp Rat". I wanted to publicize my tuning because I know people are always looking for some guidance or a rough starting point for their setup.  I have benefitted from someone else's info in the past as well.  I figured this would be a good spot as it comes up in a google search.

Pics are on Instagram and Facebook under Aspire Cycle


1978 KZ400 with original Keihin carbs. I have eliminated the airbox, installed K&N pod filters and made a custom scrambler style exhaust with 8" metal baffles from a seller on eBay. I also have a 7th Gear Designs electronic ignition setup which really pepped up the motor but caused me to have to re-jet.

I ended up with the following settings-
Idle jet 40 (plugged off)
Secondary main 75
Primary main 108
Mixture screws one full turn out from seated.

Took a ride today, April 18, had to change a few things. It seems the bike always changes after cooling off entirely.
Idle jet 40 (plugged off)
Secondary main 75
Primary main 105
Mix 1.75 turns out from seated

Hopefully this is useful to someone out there!! I'll update this thread if I make any changes. For now I'm leaving it because there are only a few days until Handbuilt Show!
« Last Edit: Apr 18, 2017, 21:55:53 by AspireCycle »

Offline AimlessMoto

  • Posts: 156
  • Blood, sweat and beers.
Re: 1978 kz400 carb tuning, k&n pods and open pipes
« Reply #1 on: May 10, 2017, 11:41:21 »
Dude, thanks for posting this! (This is AimlessMoto from Instagram.)

I had 2 KZ400's when I started, and the left carb had the pilot jet completely sheared off inside the tube.. so I had to swap the whole carb body off my second bike. Come to find out, the second bike had COMPLETELY different jets in it. The bikes are the same year, only difference is the 1st bike is a kick only (S model) and the 2nd one was an electric start (D model).

Regardless, here's my current setup:

EMGO Pod Filters spaced out with 2" PVC reducers
Stock down-pipes fitted to shorty slash-cuts, re-packed with FMF glass
Starter Jet 68 (stock)
Pilot Jet 35 (stock)
Slow Jet 40 (stock)
Primary main 135 (stock)
Main Air Jet 60 (stock)
Slow Air Jet 90 (stock)
Mix screws 1.25 turns out from soft-seat

So far, no issues, good white plug chops. Idle is a little spazzy, but I believe that's due to the pods. I did try taping off half of the pod and it ran too rich, and made no change to the idle. Then I balanced the carbs, and it seems to be much better.

ALSO... on the carb plate (choke plate) those two P-shaped O-rings... I put a SMALL run of MOTOSEAL around them (it's the only gas-proof RTV that Permatex makes) and that helped out the idle a LOT.

I'm excited to see what happens now that I've gone to a 2-into-1 high-pipe. I may have to rejet.

Offline AspireCycle

  • Posts: 2
Re: 1978 kz400 carb tuning, k&n pods and open pipes
« Reply #2 on: Nov 09, 2017, 20:59:47 »
Yours is the early model right? I think you've got a slightly different motor and carb setup than I do! I believe Kawasaki reegineered the kz400 in 77 or 78. I'll be changing my jetting again tonight. After painstakingly setting TDC I am still getting a dead spot at around 6k rpm. The thing feels like it's just hitting a wall. I'm bumping my secondary main jets up to 82 and doing a test run.