Kz750 B2 Starter Issue - among other things.

Im taking on a bike from a relative and among other things, like the bike surging and bucking like it wants to throw me off, backfiring and then shutting off after a 30 min ride, it only kicks starts. I searched the forum and see that the starter failure is a common problem.

Sounds like a new starter clutch gear is the way to go, but they dont make them anymore. Can I just kick this thing whenever I want to ride it? Im 27 with plenty of energy and though it takes some doing, Im able to get the KZ750 going with a few kicks.

I also noticed there is a crack in the airbox to carb rubber connector. Would that make the bike overheat or cause the surging and backfiring?

Thanks.

Alex

Once the bike is properly tuned, it should start on the first or second kick. 

That crack is likely adding to the problem, but not the primary cause. I bet the carb holders ( they hold the carbs to the cylinder head) are hard, cracked and leaking. Also, if the bike had been sitting unridden for a while, dried out fuel residue will be clogging the pilot circuits, causing hard starting and poor running. A complete disassembly of the carbs  and thorough cleaning with new orings and gaskets will be in order.
The fuel tank vent will need to be checked, and if the B has a vacuum petcock, it will need rebuilding.

Doing all of the items on the routine maintenance list is a great way to eliminate problems and insure smooth, reliable running.

TexasKZ wrote:

Once the bike is properly tuned, it should start on the first or second kick. 

That crack is likely adding to the problem, but not the primary cause. I bet the carb holders ( they hold the carbs to the cylinder head) are hard, cracked and leaking. Also, if the bike had been sitting unridden for a while, dried out fuel residue will be clogging the pilot circuits, causing hard starting and poor running. A complete disassembly of the carbs  and thorough cleaning with new orings and gaskets will be in order.
The fuel tank vent will need to be checked, and if the B has a vacuum petcock, it will need rebuilding.

Doing all of the items on the routine maintenance list is a great way to eliminate problems and insure smooth, reliable running.






 

Thanks so much!
I got some background for my uncle. He was diagnosed with dementia so his memory comes and goes. He told me the following and its also in his maintenance log.

1. January 2024 Carbs were rebuilt with OEM parts or similar and of good quality, o rings and all.
2. January 2024 new manual stock-style  petcock was purchased and installed.
3. The carb holders were bought in January of 2024 from Partzilla and put on in Feburary of 2024 with the newly rebuilt carbs. No cracks - garage is climate controlled,
4. The bike was put away first week of November 2024, after riding 300 miles,  with all the fluids drained - garage is climate controlled. was 60 degrees all winter in that garage and dry.
5. Starter clutch failed in late October 2024. I think when the starter clutch failed, he got bored with it and he doesnt really have the strength to kick it.

This bike is so clean it looks brand new, but my uncles 1973 kawasaki h2 mach iv 750  and h1 Mach  III's got much better care because of what they are worth.

But tell me, what is this fuel vent thing? I took the bike out today to test it again. It ran amazing for like 2 miles then started surging a little, then a little more, and then backfiring/popping. Feels, sounds, like fuel starvation, esp because of the backfiring after its been driven for a few miles. Can you tell me what to look for in the fuel vent? If its the thing underneath the gas cap, that little indentation or channel, I looked and it is clear and unclogged.

When it happens shut off the manual petcock and the motor straight away while it is faulting and pull over - then open the drains on the carbs and see if there is any fuel in them

Wookie58 wrote:

When it happens shut off the manual petcock and the motor straight away while it is faulting and pull over - then open the drains on the carbs and see if there is any fuel in them

 

Over the phone, my Dad's friend, a retiree who used to race Kawas and who built engines, said its either points, condenser, fuel tank vent issue, timing, carbs or electrical. So many possibilities, but we will see. Hes going to pick up the bike and take it back to his (45 min away) this week. 

Im a grad student and have so much studying to do its insane. I only had time today to take the bike out for 20 min and thats it. I wish I had time to do all the diagnostics.

When I discover what the problem is, I will be sure to post an update.