Kawasaki Motorcycle Forums banner

1 - 12 of 12 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hi Hope someone can help. The petcock on my Z650 B3 is the most complicated tap I have ever seen. It is a Taiyogiken contraption that doesn't even have an off position!. It has reserve at the top pre (whatever that is) at the side and On at the bottom. I have found rebuild kits online but the many replacement parts seem fine - I just can't work it out. It flows so hard that all the carbs overflow and the only time the flow from the tap stops is when it is in the ON position. Can I replace this unit with something less complicated?
 

·
Registered
Joined
·
639 Posts
Vacuum operated petcocks like yours do not need an off position. The PRI (Prime) position is only used if you ran the carbs dry of gasoline. Otherwise it should be set to the ON position. It sounds like your petcock is functioning normally.

However, your carbs should never leak gasoline from the overflow. This indicates a problem within the carbs themselves. You might have dirt in the needle valve that is preventing the automatic fuel shut off. Or the floats are set at the wrong height or are sticking. Sometimes rapping the side of the float bowl with something soft like the handle of a screwdriver is enough to unstick the floats.
 

·
Registered
Joined
·
203 Posts
Please heed WFO-KZ's advise. For fifty years I have seen the misunderstanding of the function of the petcock. The function of the petcock is a backup device to prevent catastrophic loss of fuel when the carb fails. It is not the function of the petcock fix a carb problem, only to control the situation until carb repairs are made. If the carb leaks fuel into the airbox, engine or onto the ground thru the overflows you need to address the carb problem. Relying on the petcock or any other inline shut off is only masking the problem. After fifty years of experience and having monitored numerous forums I believe the two most misunderstood systems are the petcock and valve adjustment.This goes on endlessly, Please listen to those with years of experience and practical application, it is not the job of the petcock to overcome carb failures. Find and repair the carb problem. Most older motorcycles use gravity feed fuel systems, if the carb overflowa on a gravity system it is the fault of the carb not the petcock.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #4
Fantastic! Thanks for this info. Initially I thought it was a float problem but when I realised all four carbs were overflowing at the same time I thought that unlikely. I read somewhere that a faulty petcock in these bikes could cause the overflow. I guess I'll have to bite the bullet and attack the carbies.
I have a pdf manual for 1978 and 1980. I don't suppose the carbs were any different in 1979?
 

·
Registered
Joined
·
639 Posts
With a bike this old, chances are good that you have rust or crud in the gas tank and this would explain why you have the problem with all 4 carbs. Cleaning carbs is a lot of work, so it would be a really good idea to have a close look at the inside of your gas tank and in any event, install an inline fuel filter to protect those carbs! You should also flush out the petcock.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #6
With a bike this old, chances are good that you have rust or crud in the gas tank and this would explain why you have the problem with all 4 carbs. Cleaning carbs is a lot of work, so it would be a really good idea to have a close look at the inside of your gas tank and in any event, install an inline fuel filter to protect those carbs! You should also flush out the petcock.
Thanks again.
 

·
Registered
Joined
·
19 Posts
Please heed WFO-KZ's advise. For fifty years I have seen the misunderstanding of the function of the petcock. The function of the petcock is a backup device to prevent catastrophic loss of fuel when the carb fails. It is not the function of the petcock fix a carb problem, only to control the situation until carb repairs are made. If the carb leaks fuel into the airbox, engine or onto the ground thru the overflows you need to address the carb problem. Relying on the petcock or any other inline shut off is only masking the problem. After fifty years of experience and having monitored numerous forums I believe the two most misunderstood systems are the petcock and valve adjustment.This goes on endlessly, Please listen to those with years of experience and practical application, it is not the job of the petcock to overcome carb failures. Find and repair the carb problem. Most older motorcycles use gravity feed fuel systems, if the carb overflowa on a gravity system it is the fault of the carb not the petcock.
One other misunderstood area is cam chain tension adjustment.
 

·
Registered
Joined
·
81 Posts
Fantastic! Thanks for this info. Initially I thought it was a float problem but when I realised all four carbs were overflowing at the same time I thought that unlikely. I read somewhere that a faulty petcock in these bikes could cause the overflow. I guess I'll have to bite the bullet and attack the carbies.
I have a pdf manual for 1978 and 1980. I don't suppose the carbs were any different in 1979?
The petcock will not cause the problem. But it has to fail also for a carb to leak with out the bike running. If all 4 carbs are leaking ALL 4 floats are sticking open. Plus now the petcock is not shutting off when vacuum in removed. It takes both problems for the carbs to overflow.
 

·
Registered
Joined
·
203 Posts
Actually the petcock could be functioning properly if the carbs leak when the engine is running as vac. is applied at the petcock and it is flowing normally. If they continue to leak with the engine off then the petcock has failed.
 

·
Registered
Joined
·
639 Posts
OP says "the only time the flow from the tap stops is when it is in the ON position ".
So petcock is working as it should. Therefore we must assume that the carbs are only leaking while the bike is running.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #11
Sorry I missed these follow up messages. The carbs all leak while the engine isn't running. I haven't had a chance to take them off yet but hopefully I will soon.
 

·
itching to ride
Joined
·
2,222 Posts
Rebuild the petcock first then tackle the carbs. My 454 carbs still will not shut off the fuel and it is the only bike I ever had that would not. The seats are not changeable and I have tried regrinding them to get a good polish on the float needle seat but I guess they need more work.

Pretty sure on your bike the seats are replaceable and that is what you should do along with new float needles. Also set the float height on all four carbs.
 
1 - 12 of 12 Posts
Top