petcock question

hi fellows i just bought a petcock rebuild kit for my 750 seca and mr friend was over when i pulled off the petcock i tore it apart and put it back
together exactly like it was but while i was doing it my friend kept saying his seca has a metal ring in the part you rebuild that has the square gasket with the metal piece thats in the center of it he said he beleived it went on the side where the spring is on top of the cirular metal piece thats in the center ???? anyone else have that in theirs ? if so someones rebuilt mine before and lost it im suprised it ran without it if thats true please help if you know.i can make one no problem if it does supposed to have this but im not going to if its not needed.or didnt come with it

thanks

 

You need to get a maintenance manual for your beast. The Haynes is reasonably priced and readily available. It has an ok picture of the petcock and should settle your questions easily.
You should find a metal ring between the outer cover and the petcock selector (Part #6 according to my edition of the Haynes). Your vacuum diaphragm does not have a metal ring as part of the assembly. Hit up the diagrams on Yamaha's website, they are great references and the pictures are much better than BikeBandit.com's pics.

 

As Robert mentioned, there is a "wavy" metal ring just behind the face plate that presses against the selector.

And yes there is supposed to be a spring inside the back cover that presses against the metal disk on the diaphragm. Yamaha does not break down their parts diagrams for the petcock to this level, so ordering replacements is an issue. Kawasaki used the same petcock though, and some individual parts are still available. I would have to do some research, but if you need the part numbers let me know.

I should warn you that petcock repair kits are not always successful in restoring proper function. I've seen reports that they only work like half the time. (Mine didn't.) There are additional modifications that can be tried to make it work, so let us know if you need that advice. (Although those don't always work either.)

The reason your bike still ran, even without the petcock being right, is because fuel control in our bikes is a two stage process, and the second stage was doing all the work.
1. The petcock is supposed to be the main "On/Off" switch for fuel flow. It has a vacuum operated, spring loaded valve. When the engine is running it creates a vacuum which draws the valve open to allow fuel flow. This is true for On and Reserve, but Prime simply allows fuel free-flow without the need for a vacuum. You can test your petcock by putting some fuel in the tank and:
1.a. With the selector in the On position, and no vacuum, there should be absolutely no fuel coming out. Same goes for Res. Then if switched to Pri fuel should flow.
1.b. Now attach a hose to the vacuum nipple. With the selector switched to On, draw gently on the hose like a drinking straw and fuel should flow. Release the draw and it should stop immediately. Same goes for Res.
2. Each of your carbs has a float valve. The float valve meters fuel in the carb float bowls at an appropriate level for proper running, and stops fuel flow at a maximum limit. These float valves need to function properly too, allowing the float bowls to fill, but stopping fuel flow when at a relatively precise level. There are detailed instructions on this procedure available.

Each of these two stages is important, but I put just a little more emphasis on the float valves because they stop fuel flow and influence how the bike runs. Ideally, though, the petcock should work properly too. If you have both a bad petcock, and one or more bad float valves, fuel will continue to flow when the bike is parked and leak into the air box, all over your floor, and worst of all into your crankcase mixing with your oil. A very common, although unwelcome, situation with our bikes.

Z

 

Thanks for the follow-up Z. I'm learning heaps from you fellows! I didn't draw the parallel of the "metal ring" and the diaphragm spring, doh! Glad someone here knows the intimate details (I haven't been inside of mine in over 10 years, let's hear it for factory parts!).

 

thank you rober and we yes i know about the wavy metal ring that goes behind the front plate i was asking about another supposed ring that my friend says he has in the back part as he explains it his goes over the spring (its to big in dia to touch the spring and lays on the round part thats atached to the seal itself mine does not have that and i was just wondering if anyone else did.i do have a haynes that was given to me when i bought the bike just have to locate it(never had need for it before thank god) until now i also have the original manuel that came with the bike if anyone needs any info from it ( i cant imagine you guys would but maybe some newer people may) ill be happy to pass it along.my carbs were rebuilt right before i bought the bike um let me see now that was sept of 2000 7 years yea they go definintly be for rebuild but man the bike ran so good a couple months ago we had nice days and i was riding ran idled perfect ill check into this procedure for cleaning the float pins if take those out and clean will i need to re sinc the carbs with the yics tool ?

well thank you for your replys

james

 

oh by the way from your mail i beleive my petcock is right and somone added somthing to my friends for some unknown reason.



thanks again james

 

If all your doing is polishing up the float pins, I don't see where it should effect the sync. I've heard of folks shimming stuff they don't understand very well with strange results, might be the case in your buddies assembly.

 

Hey guys some of you might have found this site ( pretty sure) but i found all kinds of scematics ( wish this thing had spell checker) for my bike! not sure about copy right but its on a web site... so i printed some off. hope it helps you guys as much as its helped me! http://www.cyclepartsnation.com/pages/p ... amaha.aspx

 

wow i pulled out my stupid haynes robert and it only shows the front assmbly doesnt show the back at all lol im glad yours does because now im positive that petcocks right and his is wrong all the schemetics on these sites have the same diagram from the haynes ( or my haynes i should say lol but i havent been able to do much with any of this anyways been feeling kinda bad the last few days besides it went back to being winter here in mich ( im soooooooo sick of it) ill get back to it when i can go in my garage for an hour without getting frozen i still need to test it like you said though wearezilla by drawing on the vacum side like a straw to see if fuel flows after the rebuild. but like a said its been so cold here and ive been feeling crappy so ill do that next an see whats up probably be back with more questions then lol

cya later guys thanks for the help
james

 

oh i meant to say this too dont worry about your spelling cannon we all mispell or mistype things sometimes ( i know i do anyways) and i knew what you meant and seen you were trying to help me out thats all that matters to me. and the rest of these guys. ive only been a member about a week and they all seem to want to help anyone without worring about spell checkers and things like that. and if i can help someone ill do it as long as they can understand what im or your saying then its good enough.thats what were all here for.

cya thanks man

james

 

I must clear up a misperception James. I said the photo in the Haynes was ok knowing it only showed the front exploded assembly. I would have said it was a good picture if it showed the backside but perhaps my perspective is flawed. I apologize if I misled you.
Please take your time getting back into the groove, you should spend most of your time resting right now, really!
Peace.