78 KZ400B Tuning Help

Remember to wear eye protection when spraying pressurized carb cleaner. Because it always backfires. Always.

Good Fortune!

Sprayed some liquid through, and shot some compressed air through. Didn't make it any better.

Think I need to start with some fresh spark plugs and go from there.

I just cant tell if it's a fuel or electrical thing. Just feels kind of like inconsistent spark, but I have a brand new points and condenser and a brand new coil on it.

Currently it idles, just pretty roughly. Then it'll accelerate, again pretty rough, but if you let off the throttle to cruise at 35 MPH it sounds just fine.

I don't know if you already have it, but the link below shows some good info on the KZ400 carbs. Ed

www.kz400.com/Workshop%20manual%20bilder...nual%20p.150-155.pdf

treitz wrote: Sprayed some liquid through, and shot some compressed air through. Didn't make it any better....

Sprayed some liquid through, and shot some compressed air through -- must of course be done precisely and not hap-hazardly.

If turning a carb pilot screw fails to produce a noticeable effect on rpm, there's probably still something wrong inside the carb (likely an imperfectly clean pilot circuit).

Good Fortune!

Sometimes there is a metal clip that holds in the main jet, and that clip has a small tab that also holds the jet plug in place.


I think I ended up making an aluminum plug using an oring to seal it. But it's been a long time. And now, the current alcohol-gasoline fuel will eat aluminum and almost any rubber except Viton.


Seems like such a simple thing... plug a small hole... but turns out they are a royal pain in the ass.

Okay... I will take the carbs off one more time to make sure all of the passageways are clean.

But seriously, is there a trick to getting these carbs off with the air box installed? Sandwiched between the motor and air box, these things are a nightmare to remove.

Your signature says it all, really.

But I always sit on the bike, put my feet on the motor, and pull the carbs into the airbox, and tip them up or down to get them out of the manifolds.

Make sure all of the airbox screws are out.
Loosen the battery box screws if necessary, or anything else that stops the airbox from moving back (it's usually the fram that determines the maximum rear-ward movement).
Make sure all of the clamps are super loose, not just loose enough, but super loose. The rubber expands as the carbs pull out.
I use a tiny bit of anti-seize on the carb outlets so they don't stick next time. But only a tiny tiny bit.

loudhvx wrote: Your signature says it all, really.

Haha yes. There is a reason I went 2-1 on my 400. HATE these stock carbs so much.

Thanks for advise loudhvx!! Cut my "off, cleaned and back on" time down to 30 minutes!

Also, taking them off, another solid clean and new spark plugs made ALL the difference. She's running great now!

Thanks for the input guys.