extremely dumb petcock question

ok. 81 maxim. brand new to me. used to Hondas where you shut off the petcock one way, center was full tank, and the other way was reserve.

i cannot figure out this petcock. as the markings are worn off.

please let me in on the secret, and i guess you have to shut it off when parking or overnight, right?

God, I feel dumb.

 

Not dumb at all. This is a vacuum operated petcock. When the bike is running the vacuum being pulled through the vacuum hose that attaches from the #3 intake manifold to just above the fuel hose on the petcock pulls open a rubber diaphragm and allows fuel to flow. Turn the engine off and the fuel flow stops. A spring keeps the rubber diaphragm closed. So the settings are "ON" , "PRI" & "RES".
Looking at the petcock straight on with the front of the bike to your left: "ON" is straight down , turning the petcock selector clockwise with the long part of the selector on the left side of the petcock will give you the "RES" setting. Which stands for reserve fuel.
Pushing the selector down and turning counterclockwise all the way to the right will give you the "PRI" setting which stands for Prime. It allows fuel to flow if the bike is not running. Mainly used to prime the carbs with fuel should the bike run out of fuel completely. So the petcock has no off position and doesn't have to be turned off like on my old Honda CB360T.

 

straight down is on, straightback is prime, straight forward is off. it took me a while to figure it out too. i had to cut the paint off of mine i guess where the previous owner painted it while on the bike.

 

oops that is right forward is reserve, dont make the mistake of running the bike with this setting, you wont get as much flow and when you runn out you are really out. if you run in the on position and run out of fuel you can switch it to reserve and run off the bottom of the tank.

 

The markings are stamped into the metal ring around the selector. If it's corroded rub it with aluminum foil. If it's painted paint stripper.

 

I knew I had a picture of a petcock on my computer somewhere...

 

Mine says "HIS - ON - HERS on it!!! 8O

 

Maybe this should just be a sticky, because I had the same issues recently, and I'm sure I'm not the only one that was confused by the lack of an "off" position on this thing....just a thought!

 

My bike has a newer yamaha replacement that is a different shape than the one that came with the bike. I'm not sure how old it is. It came with the bike and looks shiny and new.
I found it not shutting off a week ago and I had to strech the diaphram spring inside to get it to stop. It leaked into my engine and after smelling gas in my garage, I found my oil level way to high.
Works great now.

 

The one on my '83 XJ750 Maxim is different.

 

Well, well, well! And I thought they were all the same. At least "ON" is in the same position on both. That makes it a little easier.

 

thanks. you guys are the best....

 

The 550/650/750 SECA style petcock (like is shown in Gamuru's photo) has a selector lever that has a little, teensy-tiny arrow on the long, skinny edge that points in the "direction" that the selector lever is actuating---and it's really hard to see. I usually put a touch of red or white paint on that raised arrow so I'll be able to tell at a glance which "way" the lever is really pointing.

The 750 Maxims (ONLY the Maxim's, the 750 Seca petcocks are like the 550/650 versions) do not have that little arrow, but they have the word FUEL and an arrow cast into the sides of the lever....which you can't really see way down thar'......so it's not a bad idea to put a touch of paint on the the tip of that lever, too.

Oldgoat's petcock is the 100% correct petcock for all 750 Maxim models, except for the '83 Midnight Maxim, which used the same petcock but it was black.

BTW, you can use either style petcock (or the late model Yamaha don't-look-at-all-like-the-originals-but-works-just-fine petcocks) on any of the 550/650 except Turbo/750 gas tanks.

And the 550/650/750 Seca style petcocks can all be used interchangably, with the only difference is that there is a "short" and "long" style fuel outlet arm between some versions of those petcocks.

The same petcock rebuild kit can be used to rebuild ALL of these style original petcocks.

 

so what does every one recomend, a rebuild kit or diffrent petcock all together. Read on another topic of a guy that replaced his with one from z1 enterprises http://www.z1enterprises.com/detail.aspx?ID=1744. any help would be great this is my first bike so im in the dark about all this. Thanks

 

Here's the ON-OFF style FUEL VALVE similar to the one that Z1 offers. I do carry these in-stock:

http://www.xjbikes.com/Forums/viewtopic ... t=195.html

fp17) Aftermarket Complete ON-OFF-RES FUEL VALVE. Not really a "petcock" in the XJ sense of the word. Yamaha designed their petcocks to be a very clever "automatic" fuel supply valve, meaning it has to have engine vacuum for it to function. Great idea (when it works) because it allows us to basically "set it and forget it". Bad news is that when the seals go bad, or as age wears the internal components, it can become a really bad idea, since it will leak fuel into the carbs when it's not supposed to, leading to flooded carbs, fuel in the crankcase, spun bearings, etc.

This true fuel VALVE is either ON (in either the standard "ON" or the "RES"erve positions) or it's OFF. And it doesn't depend on engine vacuum, just gravity. So it won't ever leak or pass fuel in the OFF position. That's the good news. The bad news is that you have to remember to turn it on or off manually (as in every time you start your bike up or shut it down) or, instead of blaming a faulty petcock for your resultant problems, you'll have to blame yourself!

Once installed, this unit fits and looks somewhat the same as an original XJ-series petcock, what with the chrome faceplate and selector lever. It obviously has no vacuum nipple, only a rear-ward facing fuel outlet, which means you will need to remove your petcock vacuum line from the #3 intake manifold boot nipple and replace it with a rubber block-off cap plug. This fuel valve uses the same size fuel line as original.

You also must use a adapter plate on the bottom of your fuel tank that this fuel valve screws into, and the brass-mesh, in-tank fuel filter (included with this valve) is actually larger than the opening in the bottom of the gas tank (just ever so slightly), so you'll have to grind the tank opening with a dremel tool or steel file to allow the filter to go into the opening. Our complete HCP630SET (below) includes a bolt-on grinding template so you'll know exactly how much metal to remove.

All-in-all, this is a both a great value and a fine idea. It forever eliminates the dreaded "leaking petcock" problems associated with 20+ year old factory petcocks for a price just slightly more than what it costs to rebuild a factory petcock. On the downside, you will have to remember to turn this unit off or on every single time! And, once you modify your tank (by enlarging the petcock opening), an original petcock will never seal up properly to it again (or, not without alot of effort on your part to "shrink" the enlarged hole!).


550/650 (except Turbo)/750/1100 models:

HCP630SET34 Complete aftermarket FUEL VALVE KIT, contain everything you'll need to replace a factory XJ550/650 (except Turbo)/750/1100 petcock. Includes the HCP630 fuel valve, the HCP99 adpater plate, the HCP632 mesh in-tank fuel filter, the HCP1281 tank grinding template, a single HCP81 intake manifold nipple CAP PLUG, and a single HCP542 cap plug PINCH CLAMP.
$ 52.00

HCP630 Aftermarket FUEL VALVE ONLY, as used in the above complete kit. Includes the HCP632 in-tank brass-mesh fuel filter.
$ 25.00

HCP632 Aftermarket brass-mesh FUEL FILTER for the HCP630 fuel valve, filter only.
$ 11.00

HCP99 Aftermarket fuel valve-to-tank ADAPTER PLATE, includes the plate, plate-to-tank mounting screws, screw washers, die-cut plate-to-tank gasket, and a packet of gasket sealer/thread sealant. This adapter plate fits all XJ550/650 (except Turbo)/750/1100 models.
$ 24.00

HCP1281 aftermarket tank opening Grinding Template....a bolt-on thin aluminum plate that has a hole the exact size and placement needed to enlarge the petcock opening hole in the tank to accept the HCP630 fuel valve listed above. Takes the guesswork out of this critical task! This grinding template fits all XJ550/650 (except Turbo)/750/1100 models.
$ 7.00


700/900 models:

HCP630SET46 Complete aftermarket FUEL VALVE KIT, contain everything you'll need to replace a factory XJ700 or XJ900 petcock. Includes the HCP630 fuel valve, the HCP2981 adpater plate, the HCP632 mesh in-tank fuel filter, the HCP3013 tank grinding template, a single HCP81 intake manifold nipple CAP PLUG, and a single HCP542 cap plug PINCH CLAMP.
$ 52.00

HCP630 Aftermarket FUEL VALVE ONLY, as used in the above complete kit. Includes the HCP632 in-tank brass-mesh fuel filter.
$ 25.00

HCP632 Aftermarket brass-mesh FUEL FILTER for the HCP630 fuel valve, filter only.
$ 11.00

HCP2981 Aftermarket fuel valve-to-tank ADAPTER PLATE, includes the plate, plate-to-tank mounting screws, screw washers, die-cut plate-to-tank gasket, and a packet of gasket sealer/thread sealant. This adapter plate fits all XJ700 and XJ900 models.
$ 24.00

HCP3013 aftermarket tank opening Grinding Template....a bolt-on thin aluminum plate that has a hole the exact size and placement needed to enlarge the petcock opening hole in the tank to accept the HCP630 fuel valve listed above. Takes the guesswork out of this critical task! This grinding template fits all XJ700 and XJ900 models.
$ 7.00

*********************

As to your question on recommendations: well, that's a little tougher. Here's my take:

a) the factory "automatic" petcocks are hard to beat for convenience, set-it-and-forget-it purposes. As long as they are working correctly, they are an item that you never think about. They're not that hard to rebuild, but a bit tricky to rebuild "correctly" (so that they don't leak fuel).

b) the on-off fuel valve is a great little piece, but it forces you back into the "old days" routine of having to remember to turn it on and off every time your ride. If you grew up doing that, then it's not too hard to get back into that routine. If you didn't, I promise you WILL forget to perform that procedure at times, with a possibility of some unwanted results.

c) For originality purposes---if that is important to you and your goals---then rebuilding the original petcock or buying a rebuilt original petcock is the way to go (I also offer fully rebuilt original petcocks on a trade-in basis). If the automatic function is important, but not originality, the new OEM replacement style petcocks have the automatic function, but look a little bit different than the originals (but truthfully, it would have to be someone who REALLY knows their cocks....oh my!....who would notice the difference).

 

I have the same one you have on my 83