TOPIC:

This is removed from a '78 650 SR, vacuum style with two options -> on or reserve. The cap seems to be fixed on by two tabs at the side, no screws on it anywhere aside from the rear, where the diaphragm is.

It doesn't appear to compare to what I've seen on other 650's. I'll likely just replace the whole thing since my rebuilt kit clearly isn't a match. At this point I'm mostly just doing some history digging.


Ideas? Thanks

Looks like a Suzuki. somewhere around 1980. for example the 80 GS450 fuel cock lever is the same as that one.

Wow, interesting! Thanks mate. It looks near identical to the '78-80 GS750' ones.

With it having a larger diaphragm, how would that affect fuel transfer? I would think it would need an increased amount of pressure to pull gas through.

Even a vacuum petcock is a gravity fed fuel valve. The orifices are probably a standard size for Japanese motorcycles whatever that may be.
The vacuum feature is just engine vacuum pulling on a diaphragm to allow fuel to flow by gravity.
When the engine stops a spring on the diaphragm returns it to the closed position. sort of like putting your finger in a hole in a dike.

So the point of having a vacuum style switch....? To ensure your motor is drawing enough during a crank? I don't really get that part.

If it's meant to have a smaller vacuum switch than the one I've picture above, it wouldn't really have much affect on fuel allowance (because orifice size) other than vacuum required to open it?

A vaccum operated petcock disallows fuel flow when there's no vacuum being applied to the petcock, and allows fuel flow through the petcock when there is vacuum bing applied to the petcock.

A manually operated petcock requires it's lever being turned to the OFF position to disallow fuel flow through the petcock.

Good Fortune!

88kidona78 wrote: So the point of having a vacuum style switch....? To ensure your motor is drawing enough during a crank? I don't really get that part.

No.

If it's meant to have a smaller vacuum switch than the one I've picture above, it wouldn't really have much affect on fuel allowance (because orifice size) other than vacuum required to open it?


No effect on fuel flow. Likely requires less vacuum since there is a greater surface area on the diaphragm, though the strength of the spring is probably the deciding factor.

A vaccum operated petcock disallows fuel flow when there's no vacuum being applied to the petcock, and allows fuel flow through the petcock when there is vacuum bing applied to the petcock.

Yes. This way the rider does not have to do anything.

A manually operated petcock requires it's lever being turned to the OFF position to disallow fuel flow through the petcock.

Yes.

Good Fortune!

A vacuum petcock is an automatic fuel valve. When the engine is stopped, the fuel flow is stopped. When the engine is running, fuel flows.
Other than the vacuum feature, a vacuum petcock works basically the same as a manual fuel valve in supplying fuel to the carburetors.
Some riders prefer a manual fuel valve. I like the stock vacuum petcock.

Z1Enterprises.com may have an aftermarket Suzuki vacuum petcock that is a direct bolt-on & having a 44mm bolt hole spacing.
For OEM the Kawasaki KZ1000P police petcock might fit. The bolt hole spacing may be 44mm, but I am not positive.
Those police models were made thru 2005 & a new vacuum petcock should be available & at reasonable cost at some places that sell OEM.

I guess I was getting caught up on the physics of the differences.... I think I will stick with the automatic, vacuum style and leave it at that. I'll likely try one from a seller on eBay unless somebody refutes likelihood of performance. Thanks for walking me through that guys, much appreciated!

Cheers!

I DO NOT trust a vac. petcock they have a history of not closing and flooding motors and causing hydrolock in fact my 2001 Connie is waiting on a
heart transplant for that very reason.
On my KZ650 and the ZRX I used a 3/8 ball valve and have 3/8 id from tank to carbs and I turn it on and off.

How've you connected this to the tank my friend? I have considered what you've stated, but still only imagine this causing it to leak during shut-down periods and cause flooding.

Which is what happened to my bike, but it was from a degenerate aluminum plate likely from years of service. Would you simply plug the vacuum from the motor? I am sure there is a thread that discusses this.

Cheers.

He probably used a Pingel adapter plate. Z1Enterprises.com has them.
The plate bolts to the tank same as the stock petcock, then the ball valve threads into the adapter plate. Everything should be leak free.
There are manual fuel valves that fit the same as the stock petcock. Before buying a manual unit, you should verify the bolt-hole spacing.
The 1980-&-earlier 650 tanks should be 44mm. The 81 csr is 34mm. I don't know what the 82-83 650 spacing is.