76 KZ900 Plug Fouling

Maybe this old thread could help. There seems to be a lot of knowledge in it about those carbs. Good luck.   www.kzrider.com/forum/3-carburetor/60434...specs-needed?start=0

Is the bike still at 900cc?  Reason for asking is because it seems the 900's run bigger main jets than the 1000cc  bikes did, according to the service manual, anyway.  The 1000A1/2 bikes typically ran a 105 or 107.5 main, whereas the early bikes, like yours, ran 115 mains.  Guess what I'm driving at is that it might be interesting to try some smaller mains and see what happens. 

I would also perform the clear tube test and check fuel level in the float bowls.  I've seen a LOT of VM carbs where the fuel level is high, which will make the bike run rich.  Adjusting the float tang sometimes brings down the fuel level, but often it has no effect.  It's quite befuddling at times.  I've installed new float valves and not seen an improvement.  I've even resorted to new floats to fix one set of carbs.  If the floats are heavy they will sink too much, leading to a high fuel level.

Some repro exhausts are rather restrictive, another thought is do you have air corrector jets in the backs of the carbs?

And when all else fails replace the old worn out valve guide seals
Ask me how I know
DD

wrote:

And when all else fails replace the old worn out valve guide seals
Ask me how I know
DD

Ok, grab the popcorn everybody!

wrote:

I guess I was thinking that would be my next move , that or move the main jet down to a 112.5 . Not sure which one would have larger effect ?

Your current main jet is correct for a 76 KZ900 but your pilot is one size larger than stock.

What condition are your needles in?  Any sign of wear?

Float height was set with clear tube method .Bike is still 900cc . No air correcttion  jets . Needles do show a slight bit of wear.
My clymer manual (I know not always the best source) shows Main jet should be 115, and pilot 17.5 . I'm at 115 and 15.
As far as guides and seals , there is no oil residue at all on the plugs just dry black soot. 

Possible choke plungers rubbers not sealing/seating or sticky movement?

As far as valve guide seals not being a consideration  
If seals are not  up to snuff the plugs can be as you described ( Dry Black Soot )
The oil all burns up mixed with the gas  and will foul a plugs  quickly.
Sure you need to make sure the carbs are working properly,
But don't just think in the box. 
Your problem happened to me  and it turned out to be valve guide seals
Valves were all good, and had perfect compression on all cylinders
Plugs all black and fouled after  short ride
All the best 
DD
 

Choke plungers have been reconditioned with new Viton Seals.

I certainly will not rule out valve seals, once I explore all the carb scenarios .
My experience in the past with bad valve seals both on automotive and motorcycles included symptoms like, blue smoke on cold fire up, burnt oil residue on plugs, oil consumption, none of which are showing up on this bike.
Are you able to replace valve seals on these 900's without pulling the head?  

I remember Scirocco posting a valve retainer removal tool the bolted to the head somehow and acted as a lever to depress the retainer. Add compressed air into the cylinder and it might be possible. Maybe he can post the picture again?

wrote:

I remember Scirocco posting a valve retainer removal tool the bolted to the head somehow and acted as a lever to depress the retainer. Add compressed air into the cylinder and it might be possible. Maybe he can post the picture again?
 

Read about this idea some years ago.  We haven't tried it, but the idea sounds plausible.  Comments, please, regarding any downsides.

Obtain a very generous length of rawhide boot lace.

Remove the spark plug(s), and place the crank somewhere about 1/2 ~ 3/4 way into the compression stroke.  Secure one end of the lace.  Feed as much of the other end of the lace into the plug hole as necessary, allowing it to settle & wind / pile up on top of the piston.  A bore scope might be useful to see what you're doing.  Gently rotate the crank further in to the compression stroke until the piston gently contacts & compresses the layers of rawhide against the closed valve head(s), allowing the crank to to keep them firmly closed.  Now the valve keepers can be removed without the valves dropping.  No compressed air or adapters needed.

Not wishing to hijack this thread, but had to toss it out there.

We'd like to see the valve spring compressor mentioned above too!

Good Ridin'
slmjim & Z1BEBE