Yamaha Riva 180 Repair & maintenance information

Thanks I'll try to access it.

I suppose I have found the source of my leak at my pet cock.
As seen on the photos, someone has already tried to seal the thread of the water separator with Teflon band, as common in plumbing.


What he or she (yeah, right...) didn't know was, that teflon is not gasoline resistant. So I speculate that once I find the replacement for this seal ring inside there, my problem is solved. And I wont need to search for another pet cock.
The seal is a ring but not an Oring, with abount 38 mm outer diameter.
Any ideas where to get one?


Thanks for your Support

P. S: The ctc distance between the screws to the tank is indeed 46mm. I measured myself. Several old Yamaha pet cocks could fit on this gap: SR500 and some XS 650 models among others.

There is something I do not understand about this petcock. All the similar petcocks that I find on the net have the vacuum connection on the cover, and the fuel connection on the body. This petcock has them both on the body itself. So I don't understand its mode of function. What membrane will I need?
I am hesitating as to open it before I have a replacement, since I am taking in account that the 35 year old membrane might be ruined by opening.

The bowl is likely cracked or will be when you install. 35yo plastic exposed to gas does not last!

Best to have a solution for replacement.

Its a super simple design that i am sure will make sense once you open it up. Here is a couple pics i found on the internet showing it torn apart.






From Jacksscootershop (http://www.jacksscootershop.com/maintenance_tuneup_how_to.html#Fuel petcock):


Fuel petcock

This is the thing that controls the flow of fuel from the gas tank to the carb. Most of the time, it is located on the underside of the gas tank. This used to be a lever that you would have to manually turn on and off. If you forget to turn it on, your scooter will die after a short distance. Virtually all modern scooters have a petcock that works automatically. It is controlled by a vacuum line that attaches to the carb or the intake manifold. When the engine is spinning, a vacuum is drawn on the line. This will move a rubber diaphragm in the petcock, and allow fuel to flow through the petcock. As soon as the engine stops spinning, the vacuum will stop. Then the fuel flow stops. Cool, huh? As petcocks age, they can stop working. In order for the petcock to work properly, it must do at least 3 things:

1. Fuel must flow when vacuum is applied
2. Fuel must stop flow when vacuum is applied
3. Fuel should not flow from the vacuum connection into the engine

You can test the petcock to make sure it is working. It is easiest to test it when it is still connected to the gas tank. There should be two hoses running to the petcock. About 99% of the time, the smaller line is the vacuum line and the larger line is the fuel line. The fuel line will connect to the lower middle part of the carb. The vacuum line will connect to the intake manifold (between the carb and the engine) or to the back part of the carb. Disconnect both lines. Run the fuel line into a small container to catch the gas. Draw a vacuum on the vacuum line. You can do this with a vacuum tool or by mouth. As soon as the vacuum is drawn, fuel should flow. If not, you have either a bad petcock, a clogged filter screen in the gas tank, a cracked vacuum hose, or a clogged fuel line. Assuming gas flows, stop the vacuum. Fuel should stop flowing. Try this test a few times to make sure it is working properly. The petcock should be able to hold the vacuum and not leak. If it doesn't hold the vacuum it will probably need replacing soon.

I take gasket issues like that to a good hardware store. Often they can help, but bringing in the old one really is critical.

@Kevinforesthill If you dismantle it and have it in your hands and follow the routs of the vacuum, looping back and forth from the body through tiny holes in the membrane(s), the plastic plate and then into the space in the back cover, you will have to agree that it is anything but simple. I would even say, there are carburetors which are more simple than that construction.
Today I couldn't resist the urge and made my own photos (see below).
However, now I can take the time to source for new membranes (I suspect that the Seca II, the Kawasaki KX or the Suzuki DRZ400 might have somethin similar). Untill I do, I just swopped the tank with a second Cygnus that I have in my garage. My Cygnus is running again

Just wanted to correct something I wrote above (post #682): Teflon band IS gasoline resistant. At least this is what the internet sais.

Having worked with teflon commercially, it will not last when exposed to hydrocarbons.

Can you elaborate on that?
It seems to be widely used with gasoline connections, and "my" Teflon also didn't show signs of deterioration.
So what is your experience with it?

Is your other bike a BMW? Nothing to elaborate, long term exposure to hydrocarbons will deteriorate teflon.

It's a gasket, use the teflon if you want, otherwise just get a viton oring of low durometer and let it deform to seal the bowl. I would still be using the stock petcock if it did not have the plastic bowl on it. Started just like yours, a small drip, PO tried to seal threads....
Now if you could get someone to machine a bowl replacement from alloy, we would thank you very much

A BMW???
No...

I suspect that this petcock already has the machined bowl you are looking for. And the diafragm. And the gasket...

P. S: it is a gasket in there, a flat one. There is no rill to hold a Oring in place. I know cause I tried

P. P. S: and as for the Teflon, I guess I"ll stick to the information on the internet:
https://www.calpaclab.com/teflon-ptfe-compatibility/

The electronic turn signal relay works great, but sorry no vintage clicking sounds.

Nice to see you updated your taillights, its a nice upgrade.

Man, I just had some jerk throw my bike over. It was parked up on the sidewalk in front of my apartment, and I'd just had my eyes on it within the previous 10 minutes. That's San Francisco living. I spent the whole day working on it out there today, and some jerk must have taken notice and decided to teach me a lesson. And I had finally gotten the steering fixed and got to enjoy one short ride. Anyway, the left front blinker is completely smashed. Does anyone have a parts bike with a spare left front blinker they could sell me? I found a right blinker on ebay but no left. Sorry if this is the wrong forum to make that ask. Thanks.

I just did

It is always frustrating to become victim of ignorant cowards. I feel your pain.

@sanjoh in case you were wondering, this bowl I presented comes from a Honda licensed Chinese OHV snowthrower engine.

Great thread...that XC carb looks similar to the AG200 carb, except the AG carb is 26mm (Mikuni BS26), but it does have a cable operated choke exiting the top of the carb body. Just thought I'd throw it out there...

Sorry to hear about your riva. I would suggest checking eBay, I know there was a guy in placerville selling riva parts a couple months back and he would pull whatever you wanted off his complete riva.

Try getting in touch with jack@jacksscootershop.com. He's in San Jose and he's got a bunch of parts and pieces in his back yard.