Z500 for racing

not easy to diagnose form miles away, but things i would check:

quality fuel? i run all my race engines on 98-100 octane which you can find in some italian stations, if not try to put some octane aditive.

igntion timing? my CB500 and GPz550 racers run best at max 28 degrees

good fuel supply? take out the drain plug from the first carburetor bowl, open the tap, and see that it flows freely out. do the same for all cyilinders

hows the plug colors? show signs of too lean?




 

I didn’t have time to test anymore before the race but I changed to a smaller fuel filter and moved it away from the engine. 
it has run perfect all race weekend. Or maybe it’s the German 102 octane fuel I found at a gas station 🙂

Thanks for the input on the ignition. I never tested it but I will check when I get home Ignition is all standard.
My 650/750 it set to 35 after recommendations from this website  members.tripod.com/gpz_rider/technical/FAQ2000.htm

higher octane will surely cure many problems

timing depends a lot on what you done to the combustion chamber and piston crown, if there is squish or not.... the 35 is a quite standard figure for a street bike, might or might not be the best for your specific engine 

my racers always have some squish built into the combustion chamber so needed less max advance and that makes the engine more efficient and less prone to overheating/detoante

the only way to find out is to do some runs on the dyno and see what timing works best

search for "minimum best torque" timing, also known as MBT

Thanks for that advice. All my motors have some squish so maybe I can use a bit later ignition.
i will experiment with that 🙂

Today i did my second Flattrack race with the yellow and blue 650/750.
I cut some thread into the tyres. Made them a lot better.
unfortunately the gearbox started to jump from second to neutral during the race.
I thought it could be the lever bouncing on the dirttrack so I changed to “race gear shifting” with 1st up but it still happened.
I never had issues with the Z gearboxes before.
Any advice?

I should add that it happens when breaking in to a corner. I go full throttle on the straight (well not full but as much as the grip in the dirt allows) and then break with the rear brake into the corner and then when applying gas in the middle of the corner I find out I have neutral.

Two of the most common causes are worn or bent shaft forks and worn engagement dogs on the gears. (Ok, that is three, not two.)

The gear selector mechanics on the outside of the transmission could be missing its spring, could be bent or worn, or could be packed up with dirt and debris.

Did I really say two causes??

If I remember correctly I used the spring from a ZR7 that I think was stiffer. 
I will check that first before splitting the cases.
a friend told me that if the gear has 6 dogs I can remove 3 of them and backcut the remaining 3. Did anyone here try this on a 550 6-speed gearbox?

Sixten wrote:

If I remember correctly I used the spring from a ZR7 that I think was stiffer. 
I will check that first before splitting the cases.
a friend told me that if the gear has 6 dogs I can remove 3 of them and backcut the remaining 3. Did anyone here try this on a 550 6-speed gearbox?

I'm not sure that's a great idea, especially on a race bike that is being slammed through the gears - what is supposed to be the advantage of this ?

I believe the idea is that removing half the dogs creates a big play and the dogs will have time to engage fully before taking load when shifting fast.
Unless someone has tried it before I’m not sure I want to risk breaking the remaining dogs. 

Only my opinion but I think "big play" = "significant impact" on the dogs on very shift (not sure how much of that a 45 year old transmission can take !!)

I have taken it apart now and second gear only have 3 dogs already.
About aging that doesn’t seem to effect old Kawasakis 🙂 
Springs are still stiff and rubber still soft after 45 years.
I split the engine and measured everything in the gearbox according to my Kawasaki manual.
Everything is good but there is a little wear on the dogs but now so bad?



I had another 550 engine for spareparts that I took apart and that gearbox looked about the same.

Not sure what to do now.
Try and undercut second gear or revert back to the 5 speed 650 gearbox maybe. 

 

Hello. The best solution is to use the gear stack from a 600ZX secondary shaft. The 3rd and 4th idler gears rotate on a ring and not directly on the output shaft. The 600 shaft is longer than that of the 400/500/550, but everything fits together. The 600 primary shaft is identical to that of the 500/550. Only the bushing at the end of the shaft isn't drilled to allow for the clutch rod. With this improvement, the output shaft will no longer be cut by the gears rotating on it. Text translated from French with Google Translate, please be kind.