Kz750 starting problem

Hi,
Why am I having trouble starting my bike. Half the time it'll fire right up but it's a pig the other half.
Carbs have been sonically cleaned.
Coils and leads tested.
Relay mod for full power at coils
New starter clutch
Head skimmed
Valves lapped and shims all set.

I think it's slightly worse if not started for a few days.

Any ideas please?

Fuel evaporating out of the floatbowls maybe?  How about trying priming the bowls for 30 seconds or so before trying to fire it up?  Also check for plugged choke pick up tubes and the passage in the float bowls.  They often plug.

Please add your bike's exact year and model to your signature line.  There were many different KZ750 models including 2 and 4 cylinder models, and they did not all use the same carbs, ignition systems, etc.  Thanks.  Ed

Done my mistake 

I think I havnt got the option to prime,it’s just off,reserve or on. Got me thinking now though....
Carbs are definitely clean,I’ve lost count how many times I’ve stripped em. This has been going on for a looooong time. I asked this question before I did the mods and replaced starter clutch.

Most petcocks of that era have three positions: On, Res, Prime
There is no OFF.  

One other thing to check is the choke operation with the carbs installed; make sure all the choke butterflys open and close like they should when the lever is actuated.  The linkage is fiddly and delicate so you might want to check after the carbs are installed even.

The petcock has been changed hence the lack of prime,oh well that explains that.
Anyway,the starter stopped working so I stripped it and couldn't believe the state of the commutator,very worn/grooved. Also the motor was full of oil and oil that had turned to sludge. The brushes were worn to nothing.
What happened there,is there a seal on a bearing that had let the oil through?
I sourced a good used starter and the bike has been firing right up,well,so far so good.
The old starter was spinning the engine over ok but it didn't want to start. With this starter all seems well, what could have been happening?

The old starter may have been drawing so much power that there was not enough left to fire the ignition.

Problem seems solved,still starting on the button. Wish I'd looked inside the starter ages ago.
Oil leak has all but stopped too.

Well,I’m back with the same problem AGAIN!!,it sounds like the starter clutch is slipping now. I press the button and it cranks over a couple of times(but not enough to actually start it) then it stops cranking the engine and the starter motor speeds up a lot. It had a new starter clutch last year. I’m using Motul 3000 4T 20w50 standard mineral oil. Any ideas folks?

Pipes66 wrote: .................... It had a new starter clutch last year. .............

What components of the starter clutch were replaced? Ed

Complete starter clutch,a previous mechanic tried a repair kit twice so I bought the complete unit as I could see the “ramps” were very bad.