76 KZ900 Plug Fouling

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To add to HRM, not only check the needle jet is in place but you need to verify the are all the same size. Should be O-6 with 5DL31-3 needles. Make sure all slides are 1.5 cutaway. 

The 900 seems to be set up rich.  The 0-6 Needle Jet is rich, and that needle is medium skinny.  Maybe between a somewhat weak spark, rich carburation that's even richer after wear on the parts, plus compression on the low side, is all conspiring.

All from the FSM. I pulled out my ‘77 Kz1000 A1 model that used the same carb and it shows a O-6 needle jet, changed the needle to a 5CN08 needle and a 107.5 main, with the same 1.5 cutaway. Maybe that might be a better setup

I'd try a 15 pilot and a smaller main.  107.5 sounds like a reasonable starting point.  The needle may help, but those are special order, whereas jets are easier to find.

The 1977 KZ1000 LTD used the same needles, but an O5 needle jet.  It seems that there is room to experiment here.

They also used 15 pilots.

It's not clear to me which carb circuit is allowing excess fuel.  If the engine is only revving up to about 1/4 then it's probably the pilot circuit.  But if excess fuel is being delivered over the mid range then I would suspect it's the main jet system, which includes the needle jet and needle.  Since the main jets themselves have been downsized from a standard configuration I would look at changing the needles and needle jets.  I saw a significant improvement in mpg when I put new needles and needle jets into a set of Z1 carbs.  They are about the only metal part in the internals that wears.

Pretty much everything else has been looked at and confirmed...compression, timing, choke circuit, fuel level, etc.  Sherlock Holmes once said "When everyone else has been eliminated as a suspect then the logical suspect is the one remaining."  Or something like that.

Oh...one last thing to try....pull the baffles from the reproduction pipes.  Only do this in desperation.

Only yesterday did I wonder about the pipes and the difference there might be by removing the baffles. I might give it try, not much to lose at this point.

wrote:

wrote:

wrote:

wrote:

To add to HRM, not only check the needle jet is in place but you need to verify the are all the same size. Should be O-6 with 5DL31-3 needles. Make sure all slides are 1.5 cutaway. 

The 900 seems to be set up rich.  The 0-6 Needle Jet is rich, and that needle is medium skinny.  Maybe between a somewhat weak spark, rich carburation that's even richer after wear on the parts, plus compression on the low side, is all conspiring.

All from the FSM. I pulled out my ‘77 Kz1000 A1 model that used the same carb and it shows a O-6 needle jet, changed the needle to a 5CN08 needle and a 107.5 main, with the same 1.5 cutaway. Maybe that might be a better setup

I'd try a 15 pilot and a smaller main.  107.5 sounds like a reasonable starting point.  The needle may help, but those are special order, whereas jets are easier to find.

Thanks, I didn’t take availability into account.

Keyster will have complete kits for your carbs.  The link is for their Japan store.  They may also sell through dealers here in NA.

www.jp-stores.com/mc/we70630/?act=c2&c=404&icode=5484