Vacuum to manual petcock

Seems that everyone has a different preference based on their experiences.

I have only had manual petcocks on my KZ400s and I like them fine. Tip: a CB750 manual petcock is a good and easy-to-find replacement for the stock hard-to-find KZ400 manual petcock.

Two of the three ATVs that I have also have manual petcocks - never had a problem from them either. The one vacuum petcock that I do have is on my youngest son's Suzuki LT80. It failed right after I bought it while it was sitting hidden in my barn for 2 weeks before I could present it to my son for his birthday. It flooded the crankcase and caused the starter to fail (from my misguided attempts at continuing to try to start it before I diagnosed the fuel leak issue). I bought new gaskets and rebuilt it and a few weeks later was seeing the same symptoms. Then I bought a new replacement petcock which worked fine for the rest of the summer. The next spring it was showing the same issues, though not as badly as before. I ended up buying a cheap plastic shut off valve that I put in the fuel line after the petcock and we now use that to turn on or shut off the fuel.

I prefer manual petcocks.

These vac petcocks can be a pain in the butt. You could simply put an on off valve in the fuel line after the petcock. That is much cheaper that a manual petcock purchase like a pingel etc.

I will add though that the petcock does have some safety value, by cutting off gas when the engine is not running. That is more valuable that the convenience of not having to shut off a fuel switch.

What is interesting is I have run 100000+ mile on kaw vulcan 800s with a vac petcock and never had a failure. KZ petcocks seem to wear out, sometimes quickly, sometimes slowly. R

R

No eBay APP ID and/or Cert ID defined in Kunena configurationIt seems only logical that the more complex anything is, the more vulnerable it is to failure.

I have to switch to a manual petcock because my bike came with carbs from a '77, which has no vacuum port. Therefore, I have done a fair amount of research recently. The one linked below would fit a '78 and looks pretty decent to me. I would have bought one myself if it fit the CSR tank.



Barry

stratman wrote: It seems only logical that the more complex anything is, the more vulnerable it is to failure.

Barry

:lol: My wife still can't figure me out...

Just for info in case anyone doesn't know, you can use any of the 4 vacuum nipples on the intake manifold rubbers for a source of vacuum if you want to run a vacuum petcock. That's how I did it on my 77 and previous years, and it works fine. The same diaphram used in 1978 was used all the way up to 2006 on numerous models Kawasaki sold, so if it's so darn unreliable and junk, I wonder why they used it for 30yrs?

The diaphragms that failed prematurely were probably cheap aftermarket parts & not made in Japan.
Some dealers may sell an aftermarket part, unbeknownst to the customer. I've heard of this being done in regards to problematic fork seals.

RonKZ650 wrote: ..............The same diaphram used in 1978 was used all the way up to 2006 on numerous models Kawasaki sold, so if it's so darn unreliable and junk, I wonder why they used it for 30yrs?

Maybe for the same reason Lucas Electrics (the Prince of Darkness) was used on British cars for 80 years? :laugh: :laugh: Ed

RonKZ650 wrote: Just for info in case anyone doesn't know, you can use any of the 4 vacuum nipples on the intake manifold rubbers for a source of vacuum if you want to run a vacuum petcock. That's how I did it on my 77 and previous years, and it works fine.

Well that makes perfect sense, but I obviously didn't think of it. Thanks!

Reading your staunch defenses of vacuum petcocks has been little surprising to me but you obviously have enough experience to have an informed opinion. You've definitely given me a new perspective on the matter since all I've ever heard and read before was that switching to manual was the way to go.

Barry

Barry wrote:

"Reading your staunch defenses of vacuum petcocks has been little surprising to me but you obviously have enough experience to have an informed opinion. You've definitely given me a new perspective on the matter since all I've ever heard and read before was that switching to manual was the way to go."


Something else for you to think about is that a vacuum operated petcock needs a vacuum supply to fully open. Most naturally aspirated carbureted gasoline engines have very little or no vacuum at full throttle. Have vacuum gauges installed on my two trucks and they both go to near 0 in.Hg of vacuum at full throttle. Consider what happens to the fuel flow on your bike at full throttle when vacuum is very low to the vacuum operated petcock. If your bike has 1 in.Hg of vacuum at full throttle, hypothetically, does one feel confident that this is enough vacuum to overcome the spring loaded diaphragm in the petcock and allow full gasoline flow? Perhaps fuel flow gets so restricted that a extreme lean condition could develop under extended periods of full throttle. Short periods of full throttle are possibly not enough to develop a lean condition. Have converted my petcock from vacuum to manual operation as others have stated and use the PRI position for normal riding. This works okay as long as you remember to turn it off of that setting when finished riding.

Another thing to remember, but I will just have to get used to it.

Looks good! Ed

Thanks Ed,
Before long, we will all be two-wheeling again...
I'm ready to rock!