Gas petcock

Just acquired a 1982 XJ750J with 4300 miles on it. Got the carb kits/new diaphragms. The petcock is a vacuum operated style. Is there any issues with replacing it with a non vacuum style? Has anyone done this recently? I am looking for any info/problems involved. Thanks Jerry

 

Sure, you can do it, but why? The vacuum operated petcock helps protect you from having gas in the oil if one of you needle valves leaks. Unless, of course, you want to turn off your petcock every time you park the bike. They are easy to rebuild and chacal has the kits.

 

Lots of info here: http://xj4ever.com/catalog/c-petcock.html

 

The down fall of a manual petcock is forgetting to turn it on when you go for a ride. But don't worry the bike will remind you when it starts to stumble usually in the middle of a large intersection.

 

Wow... low mileage, what kind of condition is it in ?

 

Excellent condition! Not a drop of rust in tank after sitting since 1994. all electrics function as designed of course the tires are shot (split and very dry rotted) seat looks new not torn.

 

How about some photos

 

The vacume petcock, is to ensure a full flow of fuel volume to the carb bowls under heavy throttle, Im curious has anyone on here actually swaped to a standard, or blocked off the vacume side of the OEM one? did it starve for fuel?

 

Stock is always the best way to go in my opinion, they were design and engineered for a reason.

 

There is a thread on rebuilding these petcox, in the thread it states that not all petcox can be rebuilt so you must look at the petcock first before buying the kit to make sure that it can be rebuilt then even if you do rebuild it there's not always a guarantee it won't leak. It's not that the petcox were made unrebuildable it's just that some of them have issues that can't be corrected. There is also a thread some place in our forms on how to turn the vacuum pet cock into a manual petcock. This may be one part that you should consider buying a new OEM petcock I see now that places like potzilla are selling aftermarket petcox and their OEM listings so now would be the time to buy one before they vanish forever. I' know at XJ forever you can buy the OEM style or the non vacuum style.
If you float needles are working properly then it's never an issue if you leave the manual petcock on. And if you do find your crankcase full of oil your bike is just told you you need to take a look at your float needles.
I mean there are issues that will force gasoline past the needle valves that are unrelated to the condition of the bike one of them would be if you park your bike in the hot sun the gasoline expanding can force itself through the carburetors but that would only be the fuel that is passed the petcock assuming that your fuel tank vent is working properly. It would be a tiny amount of fuel. What you have to remember about the carburetors is when they sit for a while or in the hot sun the fuel is evaporating out of the carburetor bowl the air compensator gets in the overflow.

 

One of the functions of the vacuum petcock is if you drop your bike dump your bike or it falls over the fuel in the tank will not continue to flow into the carburetors as the floats will stop functioning properly and the fuel will just overflow through the overflow tubes overflows or carb compensating ports. It is kind of a safety feature if you get an accident. So if you just set your bike to prime and ride or get a manual petcock and your bike happens to fall over you're going to find all your fuel on the ground.