KZ750 1976 Engine won't start

Hi, 

(For you that do not have time to read my free text description there is a summary list below.) 

I have taken my dads old KZ750 from 1976 and I have tried to restore it to some what of its old glory. The bike was in pretty rough shape when I decided to take it on as it had been sitting in damp and moist garage for 20 year. As I started with the project there was no spark from the coil and it had to be replaced and with the new coil I got sparks and could get the motor going with some starter gas. When I later tried with fuel from the tank, I quickly got the carburettor to overflow and had to turn off the fule valve. I decide to still try to get it going with the fuel that's now was in the carburettor and to my surprise it started going for a little while and then stopped again. I tried it again with the same result. I was pleased that the motor was turning and thought that a good cleaning of the carburettor would have this bike up and running. However, after cleaning the carburettor the overflow of the bowl was fixed, but I cannot seem to get the motor started again with fuel. Not even for a little while. Not even with the choke. I get it to fire with starter gas. I tried holding my hand on the air filter inlet and after a couple of turns with the starter motor I can see and smell that I have fuel on my hand, which indicated that fuel is getting out from the bowl. I did get some backfires with the starter gas so I decided to set the ignition timing by adjusting the point (they were off). This did not help at all. Same result. Now I am a little bit out of ideas and I therefore turn to you for some guidance. Should I clean the carburettor again? Should I change anything in the carburettor? Is there a lead in the fact that an overflown carburettor bowl made it start? Do I have the wrong mixture of air and fuel? 

Thankful for all the help! 

Here is a summary of the steps taken: 

1. Plugs did not create spark 
2. Changed the ignition coil
3. Got sparks and motor turning on starter gas
4. Tried with fuel. Overflown carburettor. Did however get the motor turning with the fuel in the carburettor after turning off the fuel valve. 
5. Cleaned the carburettor
6. Re attached the carburettor. Got the motor firing with starter gas. Not with fuel. Got a backfire once
7. Set the ignition timing by setting the points. Also replaced the points and capacitor. 
8. Motor fires with starter gas, not with fuel. 

Everything you say points to a carb issue, given the age of the bike and the length of time it has been dormant I would suggest replacing the carb to head rubbers (they will almost certainly be hardened and cracked) as an air leak here will stop the fuel being drawn through the jets. Also when you cleaned the carbs did you strip them fully and ensure ALL the passages were completely clear ?

Thanks for the quick reply! I appreciate it. 

I did have the completely stripped and I had the rubber checked and there were no cracks. But as you point out, I also feel like it is the carburettor. Maybe it will be worth while to buy a refurbishment kit and exchange all the gaskets and valves. I saw something about carburettor vacuum plug. Should some of the valves be covered? 

I will leave the carb guys to get into the specifics, with the intake rubbers if they are anything like original it's probably a given that even without visible cracks they should be replaced. There are dozens of posts here where guys have visually checked and determined OK but have later replaced and found their issues are resolved.

Ah! I know what part you mean now. I was thinking of the carburettor diaphragm. I see. Well, to be honest, they are pretty stiff. I will have a look at them! 
Thanks for the guidance! And if there is anyone that have a good place to get spare parts, please do not hesitate to post a link. 

Wookie is correct, replacing the carb to head rubber manifolds will be the best first step.  Buy good quality ones, (not the under $20 chineese cheap ones).  As the carb experts here will tell you, a thorough cleaning of all carb passages  is needed. There are plenty of posts in the carburetor section covering this, and they will tell you to only replace brass parts (jets, etc ) if needed, otherwise clean. Buy quality float valve and seats. New gaskets.  The "kits" will have many parts you won't need.
Parts sources include Z1enterprises, Z1parts, Partzilla, to name a few.
There are many members here with way more knowledge and experience than I have and they are happy to help you out.
Read the post about "new owner things to know" for some great advice.
And welcome to our madness!   

Amazing! Thanks. I will have a look at the post and try to get my hands on some Carb holders as soon as possible. I will manage to get an ultra sound cleaner for work tomorrow and take the carburettor a part again. I really enjoy having the bike and cannot wait to get it started!! 

Update! 

I reopened the carburettor and had a look again. And I think it is pretty good and clean. I will re-clean everything again with carb cleaner and with an ultrasonic cleaner. Im guessing that is is difficult to remove the brass valves and fittings from the carburettor and bowl. How would one clean them the best way? I will also buy new gaskets for the bowls. 

I had a look at the diaphragm and pushing the carburettor cylinder up I can feel that is is "sucking" and opening up the carburettor top they are still intact. 
The The rubber boots as seen in the picture has seen better days but the crack are not all the way through so I do not know it that is an issue. But from what I hear from you guys it seems like the engine cannot create the vacuum needed to get fuel into the cylinders so they are most likely not sealing properly. I also took some pictures of the inlet and the cylinder valves. 

The issues with the carb mounts as well as cracking is then when they harden they don't "seal" around the circumference of the carbs

Thanks Wookie58! 

Sounds like new rubber boots would be the best way forward. Btw. Could you see the pictures I uploaded in the previous message? For me they have an Exclamation mark next to them. 

thune wrote:

Thanks Wookie58! 

Sounds like new rubber boots would be the best way forward. Btw. Could you see the pictures I uploaded in the previous message? For me they have an Exclamation mark next to them. 

 

I have fixed your pictures, next time once you have attached them click "insert all" before posting

Hi! 

If the carb holders are tight against the carburettor, would it be sufficient to have an oring/gasket between the carb holder and cylinder block? Have anyone tried that before? Just to see if the holders are the issue before I order.