'81 csr650-will only run on "Prime"

My '81 csr 650 will only run with the petcock on prime, otherwise it will stall out.
Another issue is there seems to be no reserve,I will just run the tank empty if I don't watch the mileage, does the prime setting act like it's always on reserve?

Thanks for any help

I'd check the diaphram inside the petcock(fuel valve) on the tank. It may have a crack or be blocking fuel flow.

I think Z1E has rebuild kits.

wtf ?

kawi650 wrote:

does the prime setting act like it's always on reserve?

Yes. The prime setting will draw from the bottom of the tank (reserve section)

Try this:

-Ensure the gas tank is over 1/2 full

-Turn the petcock to "ON"

-Remove the tank

-Remove the vacuum tube from the carburetors and inspect the tube to make sure there are no cracks or holes.

- Connect one end of the vacuum tube to the petcock vacuum port and try drawing a vacuum on the other end of the tube with your mouth (suck on the tube). Gas should flow out of the petcock valve. After drawing a vacuum on the line, seal the end of the tube with your tongue. Vacuum should remain in the line and fuel should continue to flow. If you get no fuel flow or you have a vacuum leak in the valve, then you'll have to pull the petcock apart and service the valve.

If you get steady fuel flow from this test with no vacuum leaks then check to make sure the carburetor vacuum port is clear and pulling a vacuum. You can test by putting your finger over the hole while the engine is running. The vacuum from the carburetor port will pulse at idle and should smooth out as the engine revs up.

Z1Enterprises.com has a K&L rebuild kit - their parts are made in Japan. I rebuilt mine a few years ago w no problems.

if your carbs are severly out of sync thm this is a realistic side effect. It's not lickly that the petcock is fucked as there is not much it other than a small plastic sheath and a few screws. I would check to make sure my lines were not rotted and then sync the carbs.

Thanks for the help!
I tried drawing on the vacuum line to get a flow out of the petcock, and it was like sucking on a pinched straw; nothing.
The vacuum line was working,when disconnected with the motor running however. Next I'll do the rebuild on the petcock.

Welcome.
This post has 2 links to two Sukuki petcoks available from Z1Enterprises tha are a dirrect swap and cost $41~$48.
forums.kz650.info/index.php?topic=1221.0

Lots have had bad luck trying to rebuild the petcocks, only to have them still leek or not work quite right.