1979 gs850 vm carb vacuum

[Atowncris]

Hello all, long time reader 1st time poster. I have been building a 1979 gs850 for a few years now and it's time to ride it. However I am having trouble with the over flows spewing fuel, I have cleaned the carbs 3 times and they still leak. Now for my ? I made my own tank and I'm not using the vacuum that goes from carb#3 to the petcock, could this be causing my problem? Should I plug the vacuum hose? Do these overflow needles and seats fail often? Thanks for the help also I would like to post a pic for all to see but can't figure it out. I did make my avatar a small pic of my bike

 

[Guest]

Greetings, welcome and all that.

Exactly how did you "clean" the carbs? Leaks are not caused by dirt, but by worn-out o-rings and gaskets. "Cleaning" the carbs should have cleaned out the passages on the inside of the carbs that will let gas get through TO the jets, then the jets themselve should have been cleaned so gas can get THROUGH them.

Your overflowing problem is likely due to improper float height, which can raise the fuel level. If you have brass floats, check them to make sure there is nothing inside them, which would also raise the fuel level. The float valves don't fail all that often, but there are gaskets under the seats that might fail.

Yes, you DEFINITELY have to plug the vacuum line from carb #3. With that open, you will have a SEVERE air leak, making #3 run VERY lean, and you will never get the carbs to sync correctly.

Click HERE to see the VM Carb Rebuild Tutorial in our 'library', then visit cycleorings.com to get a set of o-rings for your carbs. While you are there, be sure to also get the o-rings for the intake tubes and the stainless bolts that hold the tubes to the engine.

What are you using to sync the carbs?

 

[Atowncris]

Thank you I'll check the float height. I bench synced them, once it's running without spewing fuel I'll use my manometer

 

[hannibal]

Bad float needles caused my bowls to over flow. I'd first check and adjust the float. If the bowls keep overflowing or won't hold a set fuel height, the float valve needles coild be bad. I couldn't see any wear on them, but I could definitely feel a ridge with my fingernail.

 

[tkent02]

Hello all, long time reader 1st time poster. I have been building a 1979 gs850 for a few years now and it's time to ride it. However I am having trouble with the over flows spewing fuel, I have cleaned the carbs 3 times and they still leak. Now for my ? I made my own tank and I'm not using the vacuum that goes from carb#3 to the petcock, could this be causing my problem? Should I plug the vacuum hose? Do these overflow needles and seats fail often? Thanks for the help also I would like to post a pic for all to see but can't figure it out. I did make my avatar a small pic of my bike

Your language makes me think you are not really understanding how these carbs work. They are not overflow needles and seats, they are the needles and seats which control the normal fuel levels in the bowls. The overflow hoses only flow when there's too much fuel inside for some reason. If fuel is coming out of them all the time the fuel level is WAY too high.

Could be because the float is set completely wrong. Could be a chunk of crap lodged in the needle valve. Could be the float is caught under an aftermarket or home made gasket that don't fit quite right. Could be the needle and it's seat is just too worn to work correctly although it's unlikely all four would be doing this unless something isn't set up right inside. Floats can get stuck down once in a while after sitting dry a long time, sometimes smacking the bowl with something like a screwdriver handle gets them unstuck.

If all four are leaking constantly you did something wrong inside.